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[Illustration: SURVEYING STEAMER _FATHOMER_ IN MANILA BAY.
(_Frontispiece_)
]
NAUTICAL CHARTS
BY
G. R. PUTNAM, M.S.
MEMBER OF THE AMERICAN SOCIETY OF CIVIL ENGINEERS
DIRECTOR OF COAST SURVEYS, PHILIPPINE
ISLANDS, 1900 TO 1906
_FIRST EDITION_
FIRST THOUSAND
NEW YORK
JOHN WILEY & SONS
LONDON: CHAPMAN & HALL, LIMITED
1908
COPYRIGHT, 1908,
BY
G. R. PUTNAM
Stanhope Press
F. H. GILSON COMPANY
BOSTON, U.S.A.
PREFACE
In preparing the material for a lecture on Charts for Columbia
University, the writer was impressed with the fact that although
nautical charts are mentioned or discussed in many publications, there
was not found any one which covered the general subject of their origin,
construction, and use. In the countries of the world more than a million
copies of such charts are now issued annually. A considerable portion of
the human race is interested directly or indirectly, whether as mariners
or passengers or shippers, in navigation upon the sea. Aside from
supplying a handbook for those who might have a general interest in the
subject, it was thought that a discussion of charts might lead to
further consideration of the principles governing their construction.
This paper has intentionally been made as non-technical as seemed
feasible in treating a somewhat technical subject. The writer is
indebted to the Coast and Geodetic Survey for various illustrative
material from its archives, and to a number of authors for facts or
suggestions. A list is appended of books and papers which have been
freely consulted, bearing on this and related subjects.
G. R. P.
WASHINGTON, D.C., _May 24, 1908_.
CONTENTS
PAGE
LIST OF BOOKS OR PAPERS BEARING ON NAUTICAL CHARTS
AND RELATED SUBJECTS vii
CHARTS AND MAPS 1
COLLECTION OF INFORMATION FOR CHARTS 31
PREPARATION OF INFORMATION FOR CHARTS 67
PUBLICATION OF CHARTS 84
CORRECTION OF CHARTS 97
READING AND USING CHARTS 112
USE OF CHARTS IN NAVIGATION 124
PUBLICATIONS SUPPLEMENTING NAUTICAL CHARTS 154
INDEX 161
LIST OF BOOKS OR PAPERS BEARING ON NAUTICAL CHARTS AND RELATED SUBJECTS
Periplus, an Essay on the Early History of Charts, and Sailing
Directions. A. E. Nordenskiöld, Stockholm, 1897.
Maps, their Uses and Construction. G. James Morrison, London,
1902.
Charts and Chart Making. Lieut. John E. Pillsbury, U.S.N., in
_Proceedings U. S. Naval Institute, 1884_.
Principal Facts relating to the Earth's Magnetism. L. A. Bauer, in
U. S. Magnetic Declination Tables, Coast and Geodetic Survey,
1903.
Marine Hydrographic Surveys of the Coasts of the World. G. W.
Littlehales, in Report of the Eighth International Geographic
Congress, 1904.
Smithsonian Geographical Tables. R. S. Woodward, Washington, 1906.
Admiralty Charts, Abridged list of. Published by J. D. Potter,
London, 1907.
Military Topography. Capt. C. B. Hagadorn, U.S.A., West Point,
1907.
Service Hydrographique de la Marine, Paris, 1900.
A Manual of Conventional Symbols in Use on Official Charts. United
States Hydrographic Office, Gustave Herrle, 1903.
Hydrographical Surveying. Admiral W. J. L. Wharton, London, 1898.
On the Correction of Charts, Light Lists, and Sailing Directions.
Published by J. D. Potter, London, 1904.
Notes Relative to the Use of Charts. D. B. Wainwright, Coast and
Geodetic Survey, 1900.
The Law relating to Charts and Sailing Directions. H. Stuart
Moore, London, 1904.
Notes bearing on the Navigation of H. M. Ships. Hydrographic
Office, London, 1900.
The Relations of Harbors to Modern Shipping. W. H. Wheeler, in
_Engineering News_, September 6, 1906, New York.
Wrinkles in Practical Navigation. Capt. S. T. S. Lecky, London,
1899.
Navigation and Compass Deviations. Commander W. C. P. Muir,
U.S.N., Annapolis, 1906.
The Practice of Navigation. Henry Raper, London, 1898.
Lehrbuch der Navigation. Reichs-Marine-Amt, Berlin, 1906.
_The Nautical Magazine_, London.
Dangers and Ice in the North Atlantic Ocean. Bureau of Navigation,
U. S. Navy Department, 1868.
Reported Dangers in the North Pacific Ocean. U. S. Hydrographic
Office, 1871.
Pacific Islands, Vol. III, chapter on "Vigias." British
Hydrographic Office, London, 1900.
Harriman Alaska Expedition, Vol. II, Bogoslof, our Newest Volcano,
by C. Hart Merriam, New York, 1901.
Expedition to the Aleutian Islands, 1907. T. A. Jaggar, Jr., in
_The Technology Review_, 1907, Boston.
Recent Changes in Level in the Yakutat Bay Region, Alaska, by R.
S. Tarr and Lawrence Martin, in Bulletin of the American
Geological Society, 1906.
An Index to the Islands of the Pacific Ocean. W. T. Brigham,
Honolulu, 1900.
Geography, articles by C. R. Markham, A. R. Clarke, and H. R. Mill
in Encyclopædia Britannica.
Development in Dimensions of vessels, Elmer L. Corthell, Tenth
International Navigation Congress, 1905.
NAUTICAL CHARTS
CHARTS AND MAPS
#Need of maps.# Maps are useful and necessary for many purposes. Only by
means of a correct map or globe can a clear idea of the geography of a
region be given. An attempt to convey the same information by a written
description would in comparison be both cumbersome and obscure. Even by
passing over an extensive region a man unaided by instruments will
obtain only a rather crude notion of the relations, which he could
clearly see on a good map. The importance among the human arts of the
making of maps is indicated by the references to them in very early
historical records, and by the skill in map drawing shown by some of
the primitive peoples of to-day. This skill exists particularly among
races whose mode of life gives them a wide horizon, as for instance the
Eskimos. An interesting instance of this was the case of Joe, an Eskimo
guide, who, in 1898, before the surveys of the Yukon delta were made,
drew a map of the Yukon mouths with much more complete information than
any previously available.
Without attempting to enumerate in detail the special uses for maps, in
the broader sense they may be said to be essential for commercial,
engineering, military, scientific, educational, and political purposes.
#Early geography and map making.# The oldest map known is a plan of gold
mines in Nubia, drawn on a papyrus. This is of the thirteenth century
B.C., and was found in Egypt.
In the earliest historic times men believed the earth to be a flat
surface of nearly circular outline, a natural inference for those with
limited outlook and communication. Later the idea was introduced of the
ocean as a river bounding the earth disk. The spherical theory of the
earth was, however, early accepted by learned men, and was demonstrated
by Aristotle (384 to 322 B.C.), who used as proofs the earth's shadow on
the moon, and the change in the visibility of the stars in traveling
north or south. Crates constructed a terrestrial globe in the second
century B.C.
There is no Greek or Latin map extant of earlier date than the time of
Ptolemy, but there are references showing that maps were in use. One of
the first of such passages in Greek literature is the interesting
comment of Herodotus written in the fifth century B.C., "but I laugh
when I see many who already have drawn the circuits of the earth,
without any right understanding thereof. Thus they draw Oceanus flowing
round the earth, which is circular, as though turned by a lathe, and
they make Asia equal to Europe."
A map of the world was drawn by Anaximander, 560 B.C. A hundred years
later Democritus drew a map having an oblong shape, and taught that the
width of the world from east to west was one and a half times its extent
from north to south, a conclusion based on his travels eastward as far
as India. This theory, which was for a time accepted, has left an
enduring mark in the words _longitude_ and _latitude_, originally
signifying the length and the breadth of the earth.
The first application of astronomy to geography was made by Pytheas, who
about 326 B.C. obtained the latitude of Marseilles by an observation of
the altitude of the sun. Dicearchus in 310 B.C. determined the first
parallel of latitude by noting places where on the same day the sun cast
shadows of equal length from pillars of equal height. Eratosthenes (276
to 196 B.C.) was the first to compute the circumference of the earth
from observations of the altitude of the sun at Alexandria and at Syene
in Upper Egypt and an estimation of the distance between these two
places. Ptolemy, a Greek of Alexandria, in the years from 127 to 151
A.D. wrote extensively on geographic subjects, and collected into
systematic form all geographic knowledge then existing; he was the
greatest geographer of early history.
In the ten centuries which followed, part of the early advance in this
science was obscured, and the theory that the earth was a flat disk
surrounded by the sea again became prevalent. The voyages of discovery
of the middle ages, however, led to a rapid development of geographic
knowledge.
The flattening of the spherical earth was not suspected until in 1672 a
clock regulated to beat seconds at Paris, when taken to Cayenne near the
equator was found to lose two and one-half minutes a day. Newton proved
that this was due to the fact that the earth is an oblate spheroid. In
1735 accurate measurements were undertaken to determine the size and
shape of the earth. The equatorial diameter has been found to be 7926.6
miles and the polar diameter 7899.6 miles, the difference, or 27
statute miles, being the amount of the flattening at the poles.
#The first sailing directions.# The early Greek and Roman writers do not
allude to charts or maps intended especially for the use of seafarers.
There are, however, extant several peripli or descriptions of the coast.
Some of these appear certainly to have been intended for use as nautical
guides, corresponding to the modern sailing directions. It is probable
that they were explanatory of or accompanied by coast charts, now lost.
They are of interest therefore as being probably the first compilations
for the guidance of seamen. One of the earliest, written apparently in
the fifth and fourth centuries B.C., is entitled "Scylax of Caryanda,
his circumnavigation of the sea of the inhabited part of Europe and Asia
and Libya." It contains a systematic description of the coasts of the
Mediterranean, Black Sea, and part of the west coast of Africa. The
following are some extracts which indicate the character of the work. It
is to be noted that no bearings are given, and that distances are
usually stated by day's sail: Africa is referred to as Libya.
"Europe. I shall begin from the Pillars of Hercules in Europe and
continue to the Pillars of Hercules in Libya, and as far as the land of
the great Ethiopians. The Pillars of Hercules are opposite each other,
and are distant from each other by one day's sail.... From Thonis the
voyage to Pharos, a desert island (good harborage but no drinking
water), is 150 stadia. In Pharos are many harbors. But ships water at
the Marian mere, for it is drinkable.... From Chersonesus is one day's
sail; but from Naustathmus to the harbor of Cyrene, 100 stadia. But from
the harbor to Cyrene, 80 stadia; for Cyrene is inland. These harbors are
always fit for putting into. And there are other refuges at little
islands, and anchorages and many beaches, in the district between....
After the isthmus is Carthage, a city of the Phœnicians, and a harbor.
Sailing along from Hermæa it is half a day to Carthage. There are
islands off the Hermæan cape, Pontia island and Cosyrus. From Hermæa to
Cosyrus is a day's sail. Beyond the Hermæan cape, towards the rising
sun, are three islands belonging to this shore, inhabited by
Carthaginians; the city and harbor of Melite, the city of Gaulus, and
Lampas; this has two or three towers.... The sailing along Libya from
the Canopic mouth in Egypt to the Pillars of Hercules ... takes 74 days
if one coast round the bays.... From the cape of Hermæa extend great
reefs, that is, from Libya towards Europe, not rising above the sea; it
washes over them at times.... From Thymiateria one sails to cape
Soloes, which juts far into the sea. But all this district of Libya is
very famous and very sacred.... This whole coasting from the Pillars of
Hercules to Cerne Island takes twelve days. The parts beyond the isle of
Cerne are no longer navigable because of shoals, mud, and sea-weed. This
sea-weed has the width of a palm, and is sharp towards the points, so as
to prick."
That there were many other similar writings in the following centuries
is shown by the following quotation from Marcianus, in a preface to
sailing directions written in the fifth century A.D.: "This I write
after having gone through many sailing directions, and spent much time
on their examination. For it behooves all who are men of education, to
scrutinise such attempts at learning in this subject, so as neither
rashly to believe the things that are said, nor incredulously to set
their private opinions against the careful decisions of others."
The oldest extant sailing directions of the middle ages bear date 1306
to 1320.
#Development of chart making.# The application of the compass to
nautical use in the twelfth century A.D. had a marked effect in
encouraging voyages of exploration, and therefore indirectly on chart
making. The following, written toward the close of the twelfth century,
is the first known mention of the use of the compass in Europe: "The
sailors, moreover, as they sail over the sea, when in cloudy weather
they cannot longer profit by the light of the sun, or when the world is
wrapped in the darkness of the shades of night, and they are ignorant to
what part of the horizon the prow is directed, place the needle over the
magnet, which is whirled round in a circle, until, when the motion
ceases, the point of it (the needle) looks to the north." The nautical
compass of that time appears to have consisted of a magnetized needle,
floated in a vessel of water by a cork or reed, and having no index nor
compass card. Peregrinus in 1269 made notable improvements in the
compass, including a pivot suspension for the needle, a graduation, a
lubber line, and an azimuth bar for sighting on the sun or other object.
Nautical charts are known to have been in use since the thirteenth
century A.D., but the earliest extant of which the date can be fixed is
Vesconte's loxodromic chart of 1311.
The loxodromic charts first appeared in Italy, and were so called from
the fact that they were crossed by loxodromes (or rhumb lines) radiating
from a number of crossing points distributed regularly over the map.
Compass roses carefully drawn were later added at these crossing points,
the first appearing on a chart of 1375. The earliest known mention
of the variation of the compass from true north was on the first voyage
of Columbus, who discovered this important fact in 1492, and as a
consequence his "seamen were terrified and dismayed." Before that time
it was assumed in Europe that the compass pointed "true to the north
pole." The apparent failure to detect the variation earlier was
doubtless to some extent due to its small amount at that time along the
Mediterranean. The earlier charts showed both lines and compass roses
apparently oriented with the true meridian, though there is some
evidence to indicate that they were actually oriented with the magnetic
meridian, the designer not recognizing any difference. The variation of
the compass was first marked on a map in 1532 and on a printed chart in
1595, but the placing of magnetic compasses on charts did not become
customary until about fifty years ago. These early charts were drawn on
parchment, using bright colors. They were copied by hand, one from
another, with gradual variations. They had no projections, and the
draftsmen evidently had no idea of the sphericity of the earth. Islands
and points were usually exaggerated; shallows were indicated, but no
soundings; no information was given as to the interior of the countries;
a scale of distances was nearly always provided.
Charts were first printed about 1477, and are known to have been
engraved on copper by 1560.
The maps of Ptolemy were ruled with degree lines, but no chart was so
provided until 1427; by 1500, however, most charts were graduated.
Before this date it is not known on what projection the charts were
constructed. On the first graduated charts the degree lines were
equidistant parallel straight lines cutting each other at right angles
and thus dividing the chart into equal squares or rectangles. These were
known as "plain charts." This square projection had little to commend it
save simplicity of construction, as in higher latitudes it gave neither
directions nor distances correctly. The difficulties of its use in
navigation were early recognized, and nautical works contained chapters
on "sailing by the plain chart, and the uncertainties thereof."
The example of early chart making shown in Fig. 2 is of great interest
as being the earliest extant chart which includes America. This chart
was drawn on ox-hide in 1500 by Juan de la Cosa, who accompanied
Columbus on his first voyage as master of his flagship, and on his
second voyage as cartographer. The chart, of which only a portion is
shown here, purports to cover the entire world; it joins Asia and
America as one continent, the Pacific Ocean being then still unknown.
[Illustration: FIG. 2. CHART OF NORTH ATLANTIC OCEAN,]
Gerhard Krämer, a Flemish map-maker, better known by his Latin name of
Mercator, in 1569 published his famous Universal Map. In this map the
meridians and parallels were still straight lines intersecting at right
angles, but the distances between the parallels were increased with
increasing latitude in such proportion that a rhumb line, or line
cutting the meridians at a constant angle, would appear on the map as a
straight line. Mercator never explained the construction of his chart,
and as the above condition was not accurately carried out, it is thought
that the chart was drawn by comparing a terrestrial globe with a "plain
chart." After examination of a mercator chart in 1590, Edward Wright
developed the correct principles on which such a chart should be
constructed, and published in 1599 his treatise "The Correction of
Certain Errors in Navigation." It took nearly a century to bring this
chart into use, and even in the middle of the eighteenth century
nautical writers complain that "some prefer the plain chart."
[Illustration: BY JUAN DE LA COSA, 1500. EARLIEST EXTANT CHART SHOWING
AMERICA.]
The Arcano del Mare, 1646, was the first marine atlas in which all the
maps were drawn on the mercator projection.
In the sixteenth, seventeenth and eighteenth centuries charts and
sailing directions were often bound together in large volumes. These
usually had quaint titles, not overburdened with modesty, of which the
following is an example: "The Lightning Columne, or Sea-Mirrour,
containing the Sea-Coasts of the Northern, Eastern, and Western
Navigation. Setting forth in divers necessaire Sea-Cards, all the Ports,
Rivers, Bayes, Roads, Depths, and Sands. Very curiously placed on its
due Polus height furnished. With the Discoveries of the chief Countries
and on what Cours and Distance they lay one from another. Never there to
fore so Clearly laid open, and here and there very diligently bettered
and augmented for the use of all Seamen. As also the situation of the
Northerly Countries, as Islands, the Strate Davids, the Isle of Jan
Mayen, Bears Island, Old Greenland, Spitsbergen and Nova Zembla.
Adorneth with many Sea-Cards and Discoveries. Gathered out of the
Experiences and practice of divers Pilots and Lovers of the famous Art
of Navigation. Where unto is added a brief Instruction of the Art of
Navigation, together with New Tables of the Sun's Declination, with a
new Almanach. At Amsterdam. Printed by Casparus Loots-Man, Bookseller in
the Loots-Man, upon the Water. Anno 1697. With Previlege for fiftheen
years."
In 1633 a cartographer was appointed to the States-General of Holland,
and it was his duty to correct the charts from the ships' logs. The
Dutch at an early date made important progress in publishing charts. In
1720 there was established in Paris by order of the king, a central
chart office ("dépôt des cartes et plans, journaux et mémoires
concernant la navigation"), and in 1737 the first charts were published
by this office. Detailed surveys of the coast of France were commenced
in 1816.
In 1740 "the commissioners for the discovery of longitude at sea" were
authorized by Parliament to expend money on the survey of the coasts of
Great Britain, this commission having been created in 1713. Various
rewards were offered by this commission, including one of £10,000, for
the discovery of a method of determining the longitude within 60 miles,
an interesting side light on the uncertainties of navigation at that
time. Compensated timepieces, which have been so important a factor in
improving navigation, were invented by Harrison about 1761.
[Illustration: FIG. 3. LOXODROMIC CHART OF NORTH ATLANTIC OCEAN, 1565. A
PLAIN CHART WITH LATITUDE DEGREES OF EQUAL LENGTH.]
In 1795, by an Order in Council, a Hydrographical Office was established
in London, "to take charge and custody of such plans and charts as then
were, or should thereafter be, deposited in the Admiralty, and to select
and compile such information as might appear to be requisite for the
purpose of improving navigation." This office had at first one assistant
and one draftsman. Before that time many charts of a private or
semiofficial character had been published; the catalogue of the East
India Company in 1786 included 347 charts.
In 1807 the Congress of the United States authorized the President "to
cause a survey to be taken of the coasts of the United States, in which
shall be designated the islands and shoals, with the roads or places of
anchorage, within twenty leagues of any part of the shores of the United
States; and also the respective courses and distances between the
principal capes, or headlands, together with such other matters as he
may deem proper for completing an accurate chart of every part of the
coasts within the extent aforesaid." This law was the origin of the
present United States Coast and Geodetic Survey, now under the
Department of Commerce and Labor.
In 1841 a systematic survey of the Great Lakes was commenced; this is
the Survey of the Northern and Northwestern Lakes, briefly known as the
Lake Survey, conducted under the Corps of Engineers.
In 1866 the United States Hydrographic Office was established under the
Navy Department "for the improvement of the means for navigating safely
the vessels of the Navy, and of the mercantile marine, by providing
under the authority of the Secretary of the Navy, accurate and cheap
nautical charts, sailing directions, navigators, and manuals of
instructions for the use of all vessels of the United States, and for
the benefit and use of navigation generally."
#Systematic surveying and chart making# date back little more than a
century, and most of the information shown on modern charts has been
gathered in that time. At present all the principal maritime nations of
the world have made, or are extending, careful surveys of their own
coasts.
Several of the countries have added valuable contributions in the
examination of other regions and oceanic areas beyond their borders. The
maritime and colonial interests of Great Britain impelled that nation to
carry on extensive surveys along coasts whose inhabitants were not
prepared to do this work in the earlier days; the British have made
surveys along the coasts of Asia and Africa and a part of South America,
and the resulting charts have been a very important and not sufficiently
known contribution to commercial intercourse among the nations, as well
as to geography.
The Dutch, French, Spanish, and other European governments have made
nautical surveys in various parts of the world, largely in connection
with their own colonies, and in recent years much useful work has been
done by vessels of the German government. The United States has also
beyond its own territory made valuable additions to hydrographic
knowledge in the work of officers of the Navy in a number of oceanic
exploring expeditions, and surveys on the coasts of Mexico and in the
West Indies, and in the explorations of Fish Commission vessels.
[Illustration: FIG. 4. EARLY CHART OF NEW YORK HARBOR, 1737.]
#Extension of maritime surveys.# Of the total area of the earth's
surface, 51,886,000 square miles is land and 145,054,000 square miles is
sea. The oceans thus occupy nearly three-fourths of the whole surface,
affording highways open to the nations. To conduct international
commerce by water the ships of one country must enter the ports of
another. Thus both on the open sea and in the harbors there is an
interest, common to seamen of all nationalities, in the advance of
marine surveys and in the publication of charts.
To keep the coasts properly charted, as well as lighted and buoyed, is
an obligation devolving on modern nations, not only for the benefit of
their own commerce but for that of other countries.
As shown below, only a small part of the coast line of the world is
thoroughly surveyed. In the extensive ocean areas which are dotted with
islands or reefs, a large amount of work is required for their
sufficient charting, although many doubtful areas have been cleared up
in recent years. Even the parts that are known to be of depths so great
as to be free from navigational dangers should be sounded over
sufficiently to develop the general configuration of the ocean bottom.
Through international understanding a thorough exploration of all the
water area of the globe and the coasts may in time be effected, and the
many doubtful spots which still disfigure the charts may be either
eliminated or definitely located.
#Present state of progress of hydrographic surveys.# A comparatively
small proportion of the coasts of the world can be considered as
completely surveyed at the present time, and even such regions require
much additional revision. In the class of more thoroughly surveyed
coasts should be included the Atlantic and most of the Pacific coast of
the United States, Porto Rico, nearly all the coasts of Europe, Algeria,
and portions of the coasts of Japan, the Philippine Islands, and India.
A large part of the world's coasts has been surveyed incompletely, but
sufficiently well to permit the publication of navigational charts. This
is the condition as respects most of southeastern Alaska and some other
portions of the Alaskan coast, British Columbia, most of Mexico, Central
America, the West Indies, Brazil and parts of Chile, the Hawaiian
Islands, China, Malay Peninsula, Siam, the Dutch East Indies, Australia,
New Zealand, Persia, Arabia, most of Africa, Iceland, northern
Scandinavia, and Finland.
Another considerable portion of the coasts has not been surveyed, but
has been covered by explorations which have been embodied in nautical
charts of varied degrees of incompleteness. In this class are the north
coast and considerable portions of the south and west coasts of Alaska,
the Aleutian Islands, Siberia, most of the oceanic groups in the
Pacific, the northern coasts of Europe and North America, Greenland, the
west coast of South America, Venezuela, and Argentina.
Only a very small proportion of the total length of coasts is now
entirely unexplored, and such portions are confined to the polar
regions.
#Chart publications of various nations.# There are about eighteen
nations publishing navigational charts, and adding to the information on
which charts are based. Many of these nations republish to some extent
the charts prepared by the others. Great Britain has kept up a series of
charts covering all parts of the world and practically including in some
form all information published elsewhere. This series now (1908)
includes 3725 different charts, of which the annual issue is about
600,000 copies. France (1906) publishes 2948 different charts.
In the United States, charts are published by the Coast and Geodetic
Survey for the coasts and tidal waters of the main country and the
insular possessions, by the Hydrographic Office for oceanic areas and
foreign coasts, and by the Lake Survey for the Great Lakes. The total
number of different charts issued by these bureaus is about 2300, and
the total annual issue is about 225,000 copies.
#Systems in use on various charts.#
_Longitude._ The first chart of New York, published by the Coast Survey
in 1844, was referred to the City Hall of New York as the initial
longitude, and some years ago it was the prevailing custom for each
nation to use a local initial longitude. While this satisfied local
pride it led to much geographical and navigational confusion. Happily
the charts of all countries are now referred to Greenwich, with the
following exceptions:
France refers to Paris, which is 2° 20´ 15´´ E. of Greenwich.
Spain refers to San Fernando, which is 6° 12´ 20´´ W. of Greenwich.
Portugal refers to Lisbon, which is 9° 08´ 24´´ W. of Greenwich.
_Units for depths._ The English fathom or foot is used for depths on the
charts of Great Britain, the United States, and Japan. Russia uses the
sajene of seven English feet. On the modern charts of practically all
the other countries the meter is used, though on older charts various
units are found.
In the first group feet are ordinarily found only on large scale or
local charts of areas with moderate depths, and the other charts are in
fathoms, except that on the earlier charts of the Coast and Geodetic
Survey feet were used on a sanded surface inside of the three-fathom
curve and fathoms on the white surface outside of that curve. Heights
are stated in feet on the charts of the first group.
_Plane of reference._ As the depth of water varies with the tide, it is
necessary for charting purposes to adopt some standard plane to which
the soundings are referred. Practically all countries have adopted for
this purpose a low stage of the tide, as this is obviously on the side
of safety; in most cases an extreme low water is used, so that the
actual depths will seldom, owing to the tide, be less than those shown
on the chart. The definite reference planes used on the American charts
will be mentioned later.
On nearly all charts heights are referred to mean high water, doubtless
owing to this being the visible limit of the land at high tide. On
topographic maps of the interior, the heights are referred to mean sea
level, which plane is of course lower than the preceding by one-half the
range of tide.
_Symbols on charts._ Fair uniformity as to general principles, with
differences as to details in carrying them out, exists on the various
series of charts regarding their general arrangement and the more
important symbols, such as in the shading of land to distinguish from
water, the use of depth curves, the representation of hills by shade or
contour, the indication of shoals and dangers, and of lighthouses and
buoys.
#Desirability of uniformity in charts.# Ships engaged in international
commerce must enter foreign ports. As the information is constantly
changing and charts are being corrected or improved, it is sometimes
desirable for the navigator to consult the local foreign charts, and it
may often be necessary for him to carry in his chart room the charts of
several different countries. There are therefore important advantages in
international uniformity in chart publication.
There should be a common initial longitude, and as the longitude of
Greenwich has been so extensively adopted, it appears quite probable
that its use may some day become universal.
A common unit for soundings and heights would be very desirable, but the
fact that a large group of nations has united on the metric system,
while a small group with great commercial interests retains another
system, makes the attainment of uniformity difficult.
Substantial agreement as to the use of symbols on charts, particularly
such as represent aids or dangers to navigation, would be desirable and
doubtless feasible.
#Privately published charts.# Many of the earlier charts were prepared
and published by private enterprise, and such charts are still
published, as, for instance, the so-called "blue-back" charts printed in
London. These charts have usually differed from those published by the
various governments either in representing the main features in a very
bold manner with little detail or in including a considerable area with
many plans on a single large sheet backed for permanency. An objection
to the latter is that the durability together with the high price tends
to keep an old chart in use long after it is out of date. It would be
financially difficult for a private firm to give the service that a
government does in the matter of correcting the charts and issuing new
editions, and this is an important consideration in the selection of
charts.
#Purpose of charts.# The main purpose of charts is to furnish graphical
guides to aid in taking a vessel safely from one port to another; they
are maps for the use of navigators. An experienced mariner may be able
to steer his vessel over a familiar course without charts, but this does
not make their publication less necessary. Even such an expert pilot
doubtless studied the charts in the first place; the uncertainties of
the sea and the changes of information are such that his vessel's
equipment should include the latest charts, and safety requires their
examination. The passengers and the merchants who intrust their lives or
their goods to the sea are largely dependent upon the correctness of the
charts.
Besides their main purpose charts fill many other needs, among which
are; for preliminary planning of harbor improvements and various
engineering works, for defensive works and other military uses, for the
fishing interests, and for general information as to the coastal
regions. Charts will furnish much of interest and instruction to the
traveler by sea and the dweller near the coast, who will learn to read
them. Passenger steamers should more often for the interest of their
patrons display charts of the waters traversed. No written or verbal
description can give as clear an idea of geographical features and
relations as a good map or chart.
As the charts are revised from time to time, a comparison of editions at
different dates furnishes a record of the changes wrought by nature or
man, and this is especially useful in studying the action in many harbor
and river entrances, as well as for historical purposes.
#Requirements for charts.# As charts are maps of the water areas,
including the adjoining land, and intended primarily for the use of
mariners, they differ in important respects from topographic maps or
general maps, even such as include the water areas. The main
requirements for charts are these; correct and complete information,
early publication of new data, clear and intelligible representation of
the information, convenient arrangement as navigational instruments, and
high standard of publication.
The special and sometimes difficult conditions under which charts must
be used on shipboard call for good judgment throughout their
preparation. Even the paper on which they are printed is of importance,
in order that they may be sufficiently durable and suitable for
plotting.
#Information given on charts.# It is evident that it is impossible to
represent on a chart of any practicable scale all the features that
exist on the corresponding area of the earth's surface. It is
essential, therefore, that a selection be made of the classes of facts
that are to be shown, as well as of the detail that is to be used for
each class. The practical utility of the chart depends largely on the
good judgment used in this selection. In the information shown, charts
differ from maps principally in representing by soundings and curves the
configuration of the bottom of the water area, and in showing ordinarily
the topographic features only in the vicinity of the coast line.
The convenience of mariners should govern in the selection and
arrangement of the information to be shown on charts, though they may be
made useful for other purposes so long as this convenience is not
lessened. The needs and preferences of navigators alone, however, differ
so much that a reasonable chart must be somewhat of a compromise between
conflicting views. For certain classes of navigation a boldly drawn
chart showing only the dangers and a few other soundings and some
landmarks might be useful. For other maritime purposes a more detailed
chart would be valuable. The first, however, would fail to give facts
often demanded in the navigational use of the chart, and the second if
carried to an extreme would make a chart difficult to use.
[Illustration: FIG. 5. STATE OF ADVANCEMENT OF HYDROGRAPHIC SURVEYS OF
THE COASTS OF THE WORLD, 1904.
_By G. W. Littlehales._
]
Shoals and dangers are shown either by the least depth or by rock or
reef symbols. The characteristic soundings are shown on the chart, with
abbreviations indicating the nature of the bottom. Depth curves are
drawn, joining together points of like depth, and inclosing areas of
less depth, on the same principle that contours are used on land maps;
usually also the shoaler spots are made more prominent by sanding or
tinting the area within them. Lighthouses, buoys, and other artificial
aids to navigation are represented, with descriptive abbreviations. The
coast is shown by a bold solid line for high water and a dotted line for
low water. The main topographic features are represented for a moderate
distance from the coast, with such detail as is useful, depending on the
scale of the chart. Elevations are given in figures for prominent
summits, islands, and rocks; the general configuration of hills and
mountains is represented by contours on large scale charts or by
hachures or shading on small scale charts. Rivers, streams, lakes,
marshes, towns, roads, prominent buildings, and other important
topographic features are shown by appropriate symbols. It is important
that objects which may be useful in navigation as landmarks, whether
natural or artificial, be plainly shown and described, if necessary to
their identification, and that they should not be obscured by details of
lesser importance. On the larger scale charts only, vegetation features,
particularly areas covered by trees, are represented by symbols. The
land area is usually clearly distinguished from the water area by a tint
or stipple. Latitude and longitude are given by the projection
lines and the subdivided border, or sometimes on harbor plans by a note
giving the position of some one point. Brief information as to the time
and range of the tides is stated in a note. Data regarding currents,
whether due to tidal or other causes, are given by current arrows placed
on the chart, or by explanatory notes. Compasses are for convenience
printed on the charts, and data given as to the magnetic variation and
its rate of change. On large scale charts scales are provided for use in
measuring distances. Ranges and channel lines are given when required.
The ports are indicated where storm warning signals are displayed. The
areas of forbidden anchorages are shown, and when important, the
positions of submarine cables. The lines dividing the high seas from
inland waters are sometimes stated on United States charts. Life saving
stations are given, and time balls are usually noted. Views of important
features are shown on some charts.
[Illustration: FIG. 6. SYMBOLS USED ON CHARTS OF THE UNITED STATES COAST
AND GEODETIC SURVEY.]
The layman who looks at the printed chart probably does not appreciate
the amount or the variety of information that must be gathered and
sifted and put in proper shape for a single chart.
COLLECTION OF INFORMATION FOR CHARTS
#Need of thorough surveys.# As has been stated, a good chart requires
that a thorough and correct survey be first made of the region to be
charted. It is said that men are very apt to accept as true anything
they see on a map. As to the nautical chart the mariner is likely to be
somewhat more critical, however, and it is well that he is. The
difficulty of charting an invisible surface such as the bottom of the
sea is great, and the proportion of the navigable waters surveyed in
sufficient detail to be at all certain of the absence of uncharted
dangers is small.
The planning of surveys in a new region, such, for instance, as the
Philippine Islands, presents many interesting problems, on the solution
of which the effectiveness in chart results and the cost of the work
materially depend. Many local conditions must be taken into account. The
surveys are made on opposite coasts according to the seasonal winds and
rainfall. In some parts fair-sized steamers are necessary; in others
launches and small boats can do the work more economically. Shore
parties with land transportation are used for portions of the work where
the country permits. Natives are employed as far as practicable for the
classes of work they can do; the Filipinos, for instance, make good
sailors on the vessels and excellent penmen in the office.
The following is a brief outline of the steps of a complete survey for
charting purposes, according to the present practice of the United
States Coast and Geodetic Survey. These are given in their logical
order, though in actual work this order must often be departed from. In
this Survey the methods of control have been of a high standard; that
is, the main stations have been accurately determined and permanently
marked and described, and this has proven an advantage in the
joining together of the original surveys and resurveys.
#Astronomical observations.# To locate on the surface of the earth the
area to be charted, astronomical observations are required for the
latitude and longitude of one or more points. In the best practice the
longitude of a point is obtained by observing the transits of stars to
get the local time, and sending time signals by telegraph to obtain the
difference from the local time of some other place whose longitude is
known. The latitude is observed by measuring the difference of zenith
distance of pairs of stars crossing the meridian north and south of the
zenith. The azimuth or true direction of some line is also obtained from
star observations, usually by observations with a theodolite on a
circumpolar star. Much existing chart work depends on positions
determined by less accurate methods, as, for instance, longitudes
obtained by transporting chronometers between the known station and that
to be determined, or by observations of moon culminations, and latitudes
obtained by direct observations of the altitudes of stars with
theodolite or sextant.
[Illustration: FIG. 7. SYMBOLS USED ON CHARTS OF THE BRITISH
HYDROGRAPHIC OFFICE.]
[Illustration: FIG. 8. TRIANGULATION OF A BAY, SHOWING LOCATION OF
SURVEY SIGNALS AND LANDMARKS.]
#Triangulation.# The main framework of the survey consists of a series
of triangles connecting prominently located points which are permanently
marked in the ground and the location described so that they can be
found at a future time. At long intervals in the survey base lines are
laid out and carefully measured with steel tape. Signals are erected
over the points, including those at the ends of the base line, and
angles are then measured at the various stations. From the measured
length of the base and the angles the lengths of the sides of the
triangles are computed, and from these lengths and the latitude and
longitude of one point the latitudes and longitudes of all the other
points are obtained. When several astronomically determined points are
connected by such a triangulation a complication arises from what is
known as "deflection of the plumb line," which is the angular amount by
which the actual sea-level surface of the earth departs from the
symmetrical figure of revolution, owing to the variations in the density
of the earth's outer layers. The distance between two points as measured
by triangulation thus differs from the distance computed from the
astronomically determined positions. If this irregularity were not taken
care of by adopting mean positions, the discrepancy in joining up
different surveys would in extreme cases amount to about half a mile.
[Illustration: FIG. 9. TRIANGULATION STATION AND SIGNAL, ON ALASKA
COAST.]
[Illustration: FIG. 10. MEASURING ANGLES WITH THEODOLITE AT
TRIANGULATION STATION ON ALASKA COAST.]
#Survey sheets# are next prepared, of suitable size and scale. On each
sheet a projection is laid down, that is, the meridians and parallels
are drawn, and all the points determined in the triangulation are
plotted in their true relation. Usually separate sheets are prepared for
the topography or shore survey and for the hydrography or survey of the
water area.
#Topography.# The topographic survey of the shore and as much of the
adjacent area as is required is usually made with a plane table, on
which the map is actually drawn in the field as the work progresses.
Points are located on the plane table sheet either by direct reading of
the distance on a stadia rod or by intersections from two or more
stations. On the plane table sheet it is customary to locate the shore
or high-water line, the low-water line, off-lying rocks, streams,
rivers, roads, towns, lighthouses, and all prominent features near the
coast. Elevations are measured with the plane table or obtained from the
triangulation, and are represented on the sheet both by figures and by
contours, which are lines joining together points of the same elevation.
For instance, a 100-foot contour represents the line where a plane 100
feet above sea level would cut the surface of the ground. It is
particularly important in this topographic work to locate accurately
objects which are good landmarks and likely to be of use to the mariner.
In some regions auxiliary methods are used in filling in the topography,
as, for instance, along a difficult coast each feature of importance may
be located by sextant angles, or a traverse line may be run along the
shore by the transit and stadia method.
[Illustration: FIG. 11. TOPOGRAPHIC SURVEY PARTY AT WORK WITH PLANE
TABLE ON THE PRIBILOF ISLANDS.]
[Illustration: FIG. 12. SURVEY SIGNAL OF IRON PIPE ON THE BAR OFF THE
MOUTH OF THE YUKON RIVER.]
#The hydrography,# or the survey of the water area, is of prime
importance for the chart, but in the order of prosecution of the work it
is convenient but not essential that it come after sufficient points
have been located by the triangulation and topography. A hydrographic
sheet is prepared on which all the points are plotted which will be
useful. A system of sounding lines is then run over the entire area to
be surveyed, locating the position of the sounding boat at intervals by
sextant angles on survey signals or by angles from the shore. The
ordinary method of sounding is to cast a lead from a boat and read the
depth when the lead touches bottom and the line is vertical, and make
note of the nature of the bottom. There is a systematic spacing between
the casts of the lead and between the lines passed over by the boat,
depending on the depth of water and character of the bottom. For
soundings in deeper water various forms of sounding machines are used,
with weight attached to a wire. For very great depths a small steel wire
is employed and the weight is detached and left on the bottom. The
deepest sounding thus far made, 5269 fathoms, or nearly six miles, was
obtained by this method in the Pacific Ocean near Guam.
[Illustration: FIG. 13. HYDROGRAPHIC PARTY SOUNDING WITH LAUNCH IN
BALTIMORE HARBOR.]
[Illustration: FIG. 14. THE LUCAS AUTOMATIC SOUNDING MACHINE FOR DEPTHS
TO 5000 FATHOMS, WITH ENGINE.]
[Illustration: FIG. 15. THE SIGSBEE SOUNDING MACHINE ON A SURVEYING
VESSEL.]
[Illustration: FIG. 16. LONGITUDINAL SECTION OF SURVEYING STEAMER
_FATHOMER_, SHOWING GENERAL ARRANGEMENTS.]
The offshore soundings are made from a surveying steamer; the inshore
work is usually done by a launch or small boat.
So far as the navigational use of charts is concerned it is important
that the hydrography shall show the limiting depths and the freedom from
dangers, of channels, entrances, harbors, and anchorages. It is also
desirable that the soundings shall be carried off shore at least as far
as the one-hundred-fathom curve, as with the modern forms of
navigational sounding machines it is possible for vessels under way to
obtain soundings to this depth, and such soundings may be of value in
identifying the location of the vessel. For depths greater than one
hundred fathoms the soundings have less direct value to navigation
except as proving the absence of shoaler areas, but soundings throughout
the oceanic regions are of great geographical interest as well as of
direct practical value in the laying of cables.
It is obvious that the plan of mapping the sea bottom by dropping a lead
at intervals over its hidden surface is far from an ideal one. The lead
gives the depth only at the point at which it touches the bottom, and no
information as to the space between the casts except such as may be
inferred from the relation of successive soundings. In numerous cases,
after what was considered a very thorough survey of a region had been
made, at some later day a pinnacle rock or other danger has been
discovered. For instance, a very detailed hydrographic survey of
Buzzards Bay was made in 1895; the sounding lines were run at intervals
of 50 to 100 yards, and 91,000 soundings were made for a single sheet.
Within this area the cruiser _Brooklyn_ in 1902 touched a rock which
was found to have 18 feet over it. (Fig. 17.) The least depth in the
vicinity developed in the original survey was 31 feet.
For the satisfactory development of hydrographic work some invention is
much needed which as it passes along the bottom will give a continuous
depth curve. Several devices have successfully accomplished this in
shoal water, but great credit awaits the inventor who designs something
of more general application.
[Illustration: FIG. 17. PORTION OF ORIGINAL HYDROGRAPHIC SHEET, BUZZARDS
BAY, ON SCALE 1-10000, SHOWING AREA CLOSELY SOUNDED IN 1895, WHERE THE
_BROOKLYN_ STRUCK IN 1902.]
#Tides and currents.# Information must be obtained as to the movement of
the water, both vertical and horizontal. The rise and fall of the tide
are obtained by tide gauges, either automatic, which draw a continuous
tidal curve on a roll of paper, or simple tide staffs, which must be
read at intervals. The currents, whether due to the tides or other
movements, are measured by noting the movement of partially submerged
floats. Less accurate but useful information as to currents is obtained
from the logs of vessels.
[Illustration: FIG. 18. DRAGGING FOR DANGERS WITH A LONG WIRE.]
#Dragging for dangers# has long been resorted to for the investigation
of isolated spots. A valuable and successful means has been employed
recently of making sure that an area is free from shoals or rocks having
less than a certain depth. This is done by dragging through the water a
wire from 500 to 1400 feet long, and suspended at the required depth,
with suitable buoys and weights, and kept taut by the angle of pull. If,
for instance, the wire is set at a depth of 30 feet it will indicate the
presence of any obstruction of less depth by catching on it and
upsetting the buoys, and such spots are at once marked and investigated.
Considerable work has been done with such drags in the last few years on
the Atlantic and Gulf coasts and on the Great Lakes. This is of course a
somewhat tedious process and gives no information as to depths greater
than that for which the wire is set, but the experience already had
indicates its great value. It will probably be found desirable in time
to thus drag all water areas important to navigation where the depth is
near the draft of vessels and the irregular nature of the bottom gives
indication of dangers. In extensive dragging operations near Key West
and in Jericho Bay, Maine, a number of shoals have been picked up which
were not found in the original surveys.
A remarkable instance of the value of the drag was the recent discovery
of a rock in Blue Hill Bay on the coast of Maine. This rock has but 7
feet of water over it, and is only 6 feet in diameter at the top. It is
surrounded by depths of 78 feet, from which it rises nearly
perpendicularly. The original survey gave no indication of a danger
here, and its existence was not suspected until it was discovered with
the wire drag.
Another method of dragging that has been employed is by means of a pipe
suspended beneath a ship's bottom.
#Magnetic variation.# As the compass is a universal navigational
instrument, information as to the magnetic variation is needed for the
charts. The angle between the direction of the magnetic needle and the
true north is measured at various points on both land and sea, and at
some stations these observations are repeated after a number of years.
From these results magnetic maps are made, from which both the variation
and its annual change may be taken.
#Reports of dangers.# Aside from the more systematic surveys as outlined
above, much information has been placed on the charts from other
sources. On the earlier charts and on those of more remote regions at
the present day much of the work has been sketched rather than surveyed.
Even in the better surveyed portions reports come in as to dangers or
other matters not shown, and if of importance and the report appears to
be reliable these are sometimes at once put on the chart pending further
investigation, or in other cases an examination is first made.
Shoals, rocks, and even islands have in numerous instances been shown on
the charts which no one has been able to find again, and many of them
after repeated searches have been removed. The same island or danger has
sometimes been charted in two or more different positions as reported at
various times. The treatment of such cases is one of the serious and
interesting problems of the chart maker. It is generally less harmful to
show a danger which does not exist than to omit one which does exist. On
the other hand a non-existing danger shown on a chart may be the cause
of actual expense and loss of time in compelling a vessel needlessly to
go out of its course.
It is surprising to note with what lack of care and of sufficient
evidence reports of dangers at sea have sometimes been made, and how
incomplete are many of the reports even when the existence of the danger
is beyond question. It is unfortunately true that some of these reports
are the result of effort to escape blame for accident by throwing the
fault on the chart. Many such reports also result from various illusory
appearances. A large tree covered with weeds, an overturned iceberg
strewn with earth and stones, a floating ice-pan covered with earth, the
swollen carcass of a dead whale, a whale with clinging barnacles and
seaweed, reflections from the clouds, marine animalculæ, vegetable
growth, scum, floating volcanic matter, and partially submerged wrecks
covered with barnacles, have been mistaken for islands, shoals, or
reefs. A school of jumping fish has given the appearance of breakers or
caused a sound like surf, and tide rips have been mistaken for breakers.
Raper very properly calls attention to the obligation upon every seaman
of carefully investigating doubtful cases and making reliable reports.
"Of the dangers to which navigation is exposed none is more formidable
than a reef or a shoal in the open sea; not only from the almost certain
fate of the ship and her crew that have the misfortune to strike upon
it, but also from the anxiety with which the navigation of all vessels,
within even a long distance, must be conducted, on account of the
uncertainty to which their own reckonings are ever open. No commander of
a vessel, therefore, who might meet unexpectedly with any such danger,
could be excused, except by urgent circumstances, from taking the
necessary steps both for ascertaining its true position, and for giving
a description as complete as a prudent regard to his own safety
allowed."
As to the older doubtful dangers now shown on the oceanic charts, it is
estimated that the positions may be considered as uncertain by 10 miles
in latitude and 30 miles in longitude, and areas of this extent must be
searched to determine definitely the question of their existence.
The following are interesting or typical cases of reported dangers:
The master of an Italian bark in September, 1874, reported sighting a
large rock in latitude 40° N. and longitude 62° 18´ W. Fortunately for
the charts there were two independent reports from other vessels in the
same month of sighting a partially submerged wreck in this vicinity.
The Spanish steamer _Carmen_ was wrecked in 1891 by running on a rock
off the southwest coast of Leyte; the rock was reported to lie one mile
off shore, a dangerous position for vessels using Canigao Channel. A
survey made in 1903 showed 58 feet of water in this location, and
that Carmen Rock on which the vessel struck was really within one-fourth
mile of the beach. The rock had, however, for twelve years been shown on
the charts in a position which made it an obstruction to navigation.
The ship _Minerva_ in 1834 was reported to have struck a rock near the
middle of the broad entrance to Balayan Bay; the fact that this occurred
at 2 A.M. indicated a very doubtful position, but it was stated that an
American ship had previously been wrecked on the same rock. It
consequently appeared as a danger on the charts for seventy-one years,
when a survey showed no depth of less than 190 fathoms in this vicinity,
and it was removed from the charts.
A British steamer was wrecked in San Bernardino Strait in 1905; the
master reported that he was in a position where the chart showed 51
fathoms, and that he was 1-1/2 miles distant from Calantas Rock, and on
these grounds the finding of the official inquiry was that "no blame can
be attached to the master, officers, or any of the crew for the
casualty." Very shortly after the disaster, the surveying steamer
_Pathfinder_ definitely located the wreck and made a survey of the
vicinity. The previous chart of Calantas Reef was found to be fairly
correct, and the stranding was determined to have occurred well within
this reef in a position where the chart showed soundings of 3-3/4 to
4-3/4 fathoms, and 1/2 mile from Calantas Rock, which rises 5 feet above
high water.
A transport entering San Bernardino Strait a few years ago ran on a rock
and was damaged; the position was reported as about two miles southeast
of San Bernardino Island and near the middle of the passage. The rock
was not put on the charts, as prompt investigation showed 50 fathoms of
water in this vicinity, and that in all probability the transport
actually touched a small reef making out from the island.
The master of the brig _Helen_ reported that his vessel was wrecked on a
reef lying six miles from Rockall. When surveyed Helen Reef was found to
be about one-third this distance from Rockall.
An island has been reported in eight different positions, ranging in
latitude from 30° 29´ to 30° 42´ N. and in longitude from 139° 37´ to
140° 38´ E.
There have been a number of reports of islands in the area from latitude
40° 00´ to 40° 30´ N. and longitude 150° 30´ to 151° 00´ W. The master
of the bark _Washington_ reported in 1867: "On my passage from the
Sandwich Islands to the northwest coast of the United States, when in
latitude 40° 00´ N., in a dense fog, I perceived the sea to be
discolored. Soundings at first gave great depths, but diminished
gradually to 9 fathoms, when through the mist an island was seen, along
which I sailed 40 miles. It was covered with birds, and the sea swarmed
with seal and sea elephants." A United States vessel searched in
this vicinity without seeing any indication of land, and obtained
soundings of 2600 fathoms. A British ship in 1858 searched for fourteen
days over this area without finding anything. Searches were also made in
1860 and 1867 without success, and the present charts show no islands in
this part of the Pacific.
In a number of cases erroneous positions have been due simply to
blunders. Thus Lots Wife, first seen by Captain Meares in 1788, was
shown on his chart in latitude 29° 50´ N., longitude 156° 00´ E., and
stated in his book to be in latitude 29° 50´ N. and longitude 142° 23´
E. Massachusetts Island by one report was in longitude 177° 05´ E. and
by another in 167° 05´ E. The apparent blunder of 10° is now immaterial,
as the island has disappeared from the charts altogether. The Knox
Islands were placed by the Wilkes Exploring Expedition in latitude 5°
59´ 15´´ N., longitude 172° 02´ 33´´ E. The old British charts showed
islands of this name also in latitude 5° 59´ N., longitude 172° 03´ W.,
the longitude being doubtless transposed. In the case of Starbuck
Island, discovered south of the equator, the latitude was apparently
transposed, as on old charts it was also shown in the position, latitude
5° 40´ N., longitude 156° 55´ W.
A pinnacle rock can sometimes be located only with great difficulty even
when known to exist. Rodger Rock, on which the bark _Ellen_ struck and
was damaged, lies in latitude 0° 41´ 15´´ N. and longitude 107° 31´ E.
It has but three feet over it at low tide. The British surveying ship
_Rifleman_ searched four days before finding it, although the plotted
tracks showed that she and her boats had passed very close to it. This
indicates that great caution must be used in removing a reported danger
from the charts.
The old charts of the Atlantic indicated a danger 30 to 45 miles to the
southwest of Cape St. Vincent. This danger was omitted from the charts
about 1786 owing to lack of confirmation. Later, in 1813 and 1821, it
was reported that vessels were lost or damaged by striking this rock.
Soundings of over a thousand fathoms are now shown on the chart in this
vicinity and the rock no longer appears.
A comparison of a Pacific Ocean chart of about forty years ago with one
of the present time (Fig. 19) illustrates in a striking manner how many
doubtful dangers, or vigias, have gotten on the charts and how after
laborious search many of them have now been removed. This condition was
especially true of the Pacific, owing to the numerous reports of an
indefinite nature from whaling ships, among whose captains there was a
saying "that they do not care where their ship is, so long as there are
plenty of whales in sight."
[Illustration: FIG. 19. PORTION OF CHARTS OF 1869 AND 1903, OF THE
PACIFIC OCEAN WEST OF THE HAWAIIAN ISLANDS, TO ILLUSTRATE THE REMOVAL OF
DOUBTFUL DANGERS.]
[Illustration: FIG. 20. PORTION OF CHART OF PONCE HARBOR, SCALE 1-20000,
TO SHOW SELECTION OF SOUNDINGS FROM ORIGINAL SURVEY GIVEN BELOW.]
[Illustration: FIG. 21. HYDROGRAPHIC SURVEY OF SAME PORTION OF PONCE
HARBOR, REDUCED TO ONE-HALF SCALE OF ORIGINAL SHEET.]
PREPARATION OF INFORMATION FOR CHARTS.
#Chart schemes.# Before commencing the preparation of a chart it is
necessary to arrange a definite scheme for it, and the usefulness of the
chart will depend materially on this preliminary plan, in which must be
outlined its scale, size, limits, and features to be represented. New
charts have sometimes been prepared simply to fit the surveys as they
progressed or to fill immediate or local requirements. It is, however,
desirable that general plans for series or groups of charts be made, and
with changing needs, information, and conditions it is sometimes
necessary that existing schemes be modified.
#Compilation of information.# Considerable work must usually be done to
get the field records in shape for the published chart. The soundings
must be plotted and the characteristic depths selected. Only a part of
the soundings that are made can be shown on the original sheet and only
a small part of these are used on the final chart. A selection is made
showing the least soundings on shoals and bars, the channel depths, and
the characteristic soundings in anchorages and other areas. The original
surveys are generally made on a considerably larger scale than that on
which the chart is published, in order that the soundings may be more
thoroughly plotted. The sheets must then be reduced to the scale of
publication, and this can conveniently be done by means of photography
or with a pantograph.
The best judgment is required in selecting the important features
to be shown on the chart and omitting the less important and not
essential features which might tend to obscure the others. In charts of
new regions where complete surveys are lacking, care must be exercised
in weighing, combining, and adjusting information from various sources
and which is, perhaps, more or less conflicting.
#Projections.# The surface of the earth being curved, there is no
possible system of projection by which it can be represented on a flat
sheet of paper in an ideally satisfactory way. Numerous methods of
projecting the earth's surface upon a plane have been proposed and many
of them are actually used for various purposes. In general each
projection has qualities which are valuable for certain uses, and
deficiencies which make it less valuable in other ways. Only four of the
different projections need be mentioned here as of special interest in
chart construction.
#Mercator projection.# This is a rectangular projection in which the
meridians are straight lines spaced at equal intervals and the parallels
are straight lines so spaced as to satisfy the condition that a rhumb
line, or line on the earth cutting successive meridians at the same
angle, shall appear on the developed projection as a straight line
preserving the same angle with respect to the meridians.
This projection may be considered as the unrolling upon a plane of the
surface of a cylinder tangent to the earth along the equator, and upon
which the various features of the earth's surface have been projected in
such manner as to satisfy the above requirement.
On this projection there is a constant distance between the meridians,
whereas on the earth they actually converge toward the poles. The
distance between the parallels increases in passing toward the poles,
approximately in the proportion of the secant of the latitude. For each
small portion of the map the relative proportions are maintained as on
the earth.
Some characteristics of the mercator projection are these: The meridians
and parallels are all straight lines and perpendicular to each other;
there is no convergence of the meridians; the minute of longitude is a
constant distance on the map; the minute of latitude increases in length
from the equator toward the poles but locally retains its true
proportion to the minute of longitude; areas and distances increase in
scale with the latitude so that a given scale is strictly correct only
for one latitude; great circles and consequently lines of sight are
curved lines excepting the meridians and the equator; rhumb lines or
lines having a constant angle with the meridians are straight, and for
the same angle are parallel in all parts of the chart. These qualities
are all rigid and the projection can therefore be used for all areas,
small or large, up to the extent of the earth's surface, except that it
cannot be extended to the poles, as there the length of the minute of
latitude would become infinite.
An interesting fact regarding a rhumb line oblique to the meridians is
that it is a spiral continually approaching but never reaching the pole;
this spiral makes an infinite number of revolutions around the pole, and
yet it has a finite length for the reason that the length of each
revolution diminishes as the number of revolutions increases.
[Illustration: FIG. 22. MERCATOR PROJECTION OF NORTH PACIFIC OCEAN,
SHOWING GREAT CIRCLE ROUTES YOKOHAMA TO PUGET SOUND, AND YOKOHAMA TO
HONOLULU AND THENCE TO SAN FRANCISCO.]
The mercator projection has been extensively used for nautical charts,
for which it presents important mechanical advantages, in that adjacent
charts can be joined on all their edges while still oriented with the
meridian; all charts are similar; the border may be conveniently
subdivided, giving a longitude scale applicable to any part of the
chart, but a latitude scale that may be used in the same latitude only;
courses are laid down as straight lines and can be transferred with
parallel rulers from one part of the chart to another without error. On
a mercator chart an island in latitude 60° would appear four times as
large as an island of the same actual area at the equator, but this
distortion of areas, while it gives erroneous impressions on charts of
great extent in latitude, does not seriously affect the use of the chart
for nautical purposes. Areas may also be correctly measured on a
mercator map by taking each projection quadrilateral separately,
subdividing it if necessary, and using the published tables of areas of
quadrilaterals in different latitudes. Although distance scales vary
with the latitude, distances can be taken from this chart with fair
correctness by the use of the latitude border scale for the middle
latitude, subdividing the total distance if there is much range of
latitude. The inability to take off the great circle or shortest course
directly from the mercator chart is from a navigational point of view a
defect, but the most convenient solution for this appears to be the
supplementary use of a gnomonic chart as will be described. The fact
that lines of sight are not straight lines on this projection is another
defect, as by the plotting of bearings and angles on approaching the
land the positions of vessels are located on the chart; fortunately,
however, the error due to this cause usually falls within the other
uncertainties involved in locating a ship; if need be it would be
practicable to allow for this curvature. In the polar regions, however,
the faults of the mercator projection become so much exaggerated that it
is not used for navigational purposes, but because of the absence of
commercial navigation there this is a minor matter in the general
question of chart projection. For the plotting of original surveys the
mercator projection is not suited and is not used, for the reasons above
mentioned.
[Illustration: FIG. 23. POLYCONIC PROJECTION OF PORTION OF NORTH PACIFIC
OCEAN.]
Tables of "meridional parts" are published which give the distance in
terms of minutes of longitude from the equator to the various parallels;
with these tables a mercator projection may readily be constructed.
Airy proposed a graphical method of sweeping the arc of a great circle
on to a mercator chart, and tables are published for this purpose. The
method is only approximate and is limited in application, and the
supplementary use of a gnomonic chart would appear to be preferable.
#Polyconic projection.# In plotting the original surveys it is essential
that a projection be used which will for the area included on a survey
sheet show the points in their correct relation both as to direction and
distance. These conditions are substantially fulfilled by several
projections, of which the polyconic is used in the United States. If a
hollow cone were placed so that it would either be tangent to the
earth's surface along one of the parallels of latitude or cut it along
two parallels, and the points projected on to this cone, and the cone
then unrolled and laid out flat, the result would be a conical
projection, of which there are several variations. If successive tangent
cones be used and each parallel of latitude be developed as the
circumference of the base of a right cone tangent to the spheroid along
that parallel, the result is the polyconic projection, which has been
used for field sheets and for the large scale charts, as well as for the
topographic maps of the United States. This projection has valuable
qualities for moderate areas of the earth's surface, within which the
scale is approximately uniform, areas retain nearly their true
proportions, and great circles and consequently all bearings and
directions are approximately straight lines. The parallels of latitude
are arcs of circles with radiuses increasing as we recede from the pole;
therefore they are not truly parallel and the length of the degree of
latitude increases either side from the central meridian. The meridians
converge toward the poles and become slightly curved as we recede from
the central one; the longitude scale is everywhere correct, but the
latitude scale is strictly correct only on the central meridian. The
angles of intersection of parallels and meridians are right angles or
nearly so. The polyconic projection is not used for very extensive areas
of the earth's surface, as for instance a hemisphere.
[Illustration: FIG. 24. GNOMONIC CHART OF NORTH PACIFIC OCEAN, SHOWING
GREAT CIRCLE ROUTES YOKOHAMA TO PUGET SOUND, AND YOKOHAMA TO HONOLULU
AND THENCE TO SAN FRANCISCO.]
#Gnomonic projection.# In this projection the eye is assumed to be at
the center of the earth and the features are projected upon a plane
tangent to some point on the earth's surface. It is practicable to use
this projection for oceanic areas, and it has the very important quality
that every straight line on it represents a great circle of the earth.
To obtain the great circle or shortest course between two points it is
therefore only necessary to draw a straight line between the points on a
gnomonic chart. Because of the great distortion near the edges this
projection is not otherwise adapted to navigational use, and it is
employed only to mark out the general course, and sufficient points are
then transferred to a mercator chart. The gnomonic chart is therefore
useful in supplementing the mercator chart, supplying its deficiencies
as to convenience in marking out great circle courses. The great circle
course can be derived not only more easily and quickly from the gnomonic
chart than by computation, but the chart is also to be preferred because
the course marked out on it will show at once if any obstruction, as an
island or danger, is met or too high a latitude is reached. A modified
or composite course can readily be laid out on a gnomonic chart.
[Illustration: FIG. 25. NORTH POLAR CHART ON ARBITRARY PROJECTION.]
#Arbitrary projection.# The few charts published of the polar regions
are sometimes on an arbitrary projection, in which the meridians are
straight lines radiating from the pole and the parallels are equidistant
circles with the pole as center. The latitude scale is uniform. At some
distance from the pole the longitude scale becomes very much distorted,
but the projection is a practicable and convenient one for the immediate
polar regions. Gnomonic and conical projections are also used for the
polar charts, differing little from the foregoing for moderate areas.
#Scales.# Charts are published on a variety of scales to suit different
needs of navigation, and the usual classification depends on scale. In
addition to the ocean charts covering a single ocean in either one or
several sheets and intended for navigation on the high seas,
there are for our Atlantic coast the following series:
Sailing charts, scale about 1/1200000, for general coastwise navigation.
General coast charts, scale 1/400000, for local coastwise navigation.
Coast charts, scale 1/80000, for approaching the coast at any point and
for inside passages.
Harbor and channel charts, of various large scales from 1/5000 to
1/60000, for entering harbors and rivers and passing through channels.
The expression of scales by miles to the inch or inches to the mile is
the more familiar. The expression of scale in the manner used by the
Coast Survey and by most of the European countries, by standard
fractions as 1/80000, meaning that any distance on the chart is 1/80000
of the actual distance on the earth, has some advantages. For instance,
the relation of these fractions gives at a glance the relation of the
scales of the charts. Thus a 1/80000 chart is on a scale five times as
large as a 1/400000 chart.
For the more important harbors charts have been published on several
different scales to meet various needs. Thus New York Harbor is shown on
charts of scales of 1/10000, 1/40000, 1/80000, 1/200000, 1/400000 and
1/1200000, each of course including a different area.
[Illustration: FIG. 26. NEW YORK HARBOR, PORTIONS OF CHARTS ON FOUR
DIFFERENT SCALES.]
The selection of suitable publication scales is of prime importance; a
large scale permits of greater clearness and of showing more detail, but
on the other hand restricts the area and the points that can be shown on
a single sheet, or else makes a chart of excessive dimensions. In
general in chart preparation the scale should be restricted to the
minimum that can be used to fulfill the particular object and clearly
represent what is desired. A chart of very large scale is not convenient
for plotting, and a moving vessel may pass quickly beyond it or into
range of objects beyond the limits of the chart.
PUBLICATION OF CHARTS.
#Methods of publication.# An ideal process of publication for nautical
charts would include the following features; rapidity in getting out new
charts, facility in reprinting and correcting existing charts, clearness
and sharpness of print, durability of paper and print, and correctness
of scale. It is difficult to fulfill all these requirements by any
method as yet developed. In the Coast and Geodetic Survey several
different processes are in use at present; charts are engraved on copper
and printed directly from the copper plate, or they are transferred from
the copper plate to stone and printed from the stone, or a finished
drawing is made and transferred to stone by photolithography and printed
from the stone, or an etching is made on copper from a finished drawing
and printed from a transfer to stone. Charts in other countries are in
large part printed from engraved plates, excepting some preliminary
charts by lithography.
[Illustration: FIG. 27. ENGRAVING A CHART ON A COPPER PLATE.]
[Illustration: FIG. 28. ENGRAVING SOUNDINGS ON A COPPER PLATE WITH A
MACHINE.]
#Copper plate engraving and printing# have long been used in chart
preparation. A drawing is prepared as a guide for the engraver; this
must be correct as to all information to be shown but need not be a
finished drawing. A true projection is ruled upon a copper plate. By
photography a matrix is made from the drawing and a wax impression taken
from this matrix. This is then laid down on the copper to fit the
projection, and the impression is chemically fixed on to the copper. The
work thus marked out is engraved by hand or by machine. A high degree of
skill is required in the accuracy and finish necessary for chart
engraving. Machines have been invented in recent years which can be used
for portions of the work on copper plates, as for instance for cutting
the sounding figures, the bottom characteristics, the border and
projection lines, border divisions, compasses, line ruling, and stipple
ruling. Stamps and dies have been successfully used for some symbols and
notes, and roulettes for shading. By means of these various machines,
many of which are American inventions, the process of chart publication
from plates has been materially facilitated.
[Illustration: FIG. 29. ELECTROTYPING PLANT FOR ELECTROTYPING CHART
PLATES.]
When the plate is completed an alto, or raised copy, is made by
depositing copper on to it in an electrotype vat, and from this alto
another basso or sunken copy is made by the same process. This latter
basso is used in printing. A copper plate may be used for about 3000
impressions, after which it may become too much worn for satisfactory
chart printing. By printing from a duplicate basso the original plate is
preserved and additional copies can be made when needed. The use of the
alto also greatly facilitates matters when a considerable correction to
the chart is required. All the portions of the chart to be changed can
be scraped off the alto, and when a new basso is electrotyped from this
scraped alto all such areas will of course appear as smooth copper, on
which the new work can be engraved. Numerous small corrections are
called for on charts, and on copper plates where these are to replace
old work the latter is removed either by hammering up the back of the
plate or by scraping its face.
Printing directly from plates is a laborious process. After the press
bed has been carefully padded to take up inequalities in the plate, the
surface of the latter is covered with ink and then carefully wiped off
by hand, leaving the ink only in the engraved lines. The paper, first
dampened, is laid on the plate, and passes with it beneath the cylinder
of the press under considerable pressure. The prints are calendered by
being placed in a hydraulic press under 600 tons pressure. The charts
are beautifully clear and sharp, not equalled by other methods of
printing. Owing to the wetting and drying of the paper, the finished
print is, however, quite appreciably smaller in scale than the plate,
and the shrinkage is greater in one direction than in the other. The
average day's work for one press and two men is 75 prints. This is small
compared with the output practicable with lithographic presses. On the
other hand a plate can be prepared for printing more readily than a
lithographic stone. For small editions the plate printing compares well
in economy with lithographic printing, and the plate can also be printed
on short notice. Because of changes in aids to navigation and other
corrections, it is usually desirable to print at one time only a
sufficient number of copies of a chart to meet current demands, and not
to carry a large stock on hand.
[Illustration: FIG. 30. PRINTING CHARTS FROM COPPER PLATES; FINAL
CLEANING OF THE PLATE BY HAND; PLATE PRESS ON THE LEFT.]
The copper plates, bassos, and altos make a very convenient and enduring
means of preserving the chart ready for printing or for further
correction. A large number of plates can be placed in a small space, and
if properly cared for they may be stored indefinitely without
deterioration.
With plate printing it is not practicable to print more than one
impression on the chart or to use more than one color, and plate-printed
charts are therefore in black only.
[Illustration: FIG. 31. LITHOGRAPHING PRESSES FOR PRINTING CHARTS;
LITHOGRAPH STONE ON TRANSFER PRESS.]
#Engraving on stone.# On the United States Lake Survey the charts are
first engraved on stone, and by a special process the work is then
transferred to small copper plates, which are preserved. The final
publication is by lithography, transferring again from the plates to
stone.
#Photolithography# is a quick method of publishing a chart. It would be
practicable by this means to reproduce the original survey sheets, but
ordinarily these are not suitable as to scale and legibility, and it is
necessary to make a new drawing, usually on tracing vellum. This is
photographed on to glass plates, on the scale of the proposed chart.
From these glass negatives positive prints are made on sensitized
lithographic paper. These prints are fitted together and then inked,
taking the ink only where the lines appear. This transfer print is then
laid face down on the lithographic stone and run through a press under
pressure, the stone absorbing the ink from the paper. The stone is then
treated so that the inked portion remains slightly raised, and from this
stone an indefinite number of charts can be printed in a lithographic
press at the rate of 1000 an hour. The paper is not moistened, and
consequently there is little distortion or change of scale in prints
from stone. If desired to shade the land or use another color for any
other purpose, additional impressions can be made on the same charts
from other stones. Because of the bulk of the stones, work cannot
ordinarily be retained on them, but the chart is cleaned off and the
stones repeatedly used until worn thin. The original drawing as well as
the negatives is preserved, from which the chart can again be published.
For republication, the process is, however, not entirely satisfactory;
the negatives are not always permanent, the work must again be assembled
and transferred to the stone, changes or corrections are not very
conveniently made on either drawing or negative, and after repeated
changes the drawing becomes difficult to use in photolithography.
Whether the charts are actually printed from copper or stone, there are
decided advantages therefore in the matter of correction work and future
editions in having the charts engraved on copper. On the other hand, the
advantages of the photolithographic process are the ability to publish
new drawings promptly, to use more than one shade on a chart, to obtain
prints with little change of scale or distortion, and to print large
editions rapidly.
#Lithographic printing by transfer from engraved plates.# An impression
on transfer paper may be taken from an engraved plate and this laid down
on the stone in a manner similar to that used in laying down the prints
from the glass negatives in photolithography. Prints are then made from
the stone the same as in photolithography, but with superior results as
to clearness. This general process is extensively used in both map and
chart publishing in this country, as it combines the advantages of the
plate in preservation of the chart record and facility of correction,
and the advantages of the lithographic printing in less distortion of
the printed chart, ability to print more than one shade, and facility
for large editions. As the transfer from the plate can be readily made
it is also better applicable to small editions than is photolithography.
It is, however, not as convenient in the latter respect as plate
printing, and it does not give a resulting impression equal in clearness
or durability to the impression directly from the plate.
#Etching on copper# for chart publication has been recently developed in
the Coast and Geodetic Survey. A finished tracing is made, the surface
of a smooth copper plate is sensitized, and by exposure to the sun a
print is made on the sensitized surface. It is essential to use an
air-exhausted printing frame so as to get good contact between the
vellum and the plate. The work is then etched into the copper and the
plate cleaned and touched up, after which it may be used the same as a
hand-engraved plate, either for transfer to stone or direct plate
printing. The expense and time required in the etching process are much
less than for hand engraving. The process has been successfully used for
a number of harbor charts. The etching of course will be of the same
scale as the vellum at the time of the print, and vellum varies somewhat
in scale with weather conditions and age. Unless overcome by the
substitution of some more invariable material in place of vellum, this
might be an obstacle to the use of the process for general charts where
a true scale on the copper plate is desirable because of future work to
be done on the plate. It must also be taken into account that the
etching requires a finished tracing in ink, which is not essential for
the hand engraver; if, however, the chart is first published by
photolithography, as is the usual practice in the Coast and Geodetic
Survey, the same tracing is used for both processes.
#Distribution of charts.# Charts published by the government are sold to
the public at a small price, estimated to cover the cost of paper and
printing. The charts may be obtained direct from the publishing office
or from the chart agents who are to be found in all the principal
seaports. Catalogues are published from time to time giving complete
lists of the current charts and the main facts regarding them. Index
maps show graphically the area covered by each chart. The notices to
mariners contain announcement of new charts or new editions published
and of charts or editions cancelled, as well as of all corrections.
CORRECTION OF CHARTS.
#Need for revision.# The making of the survey and the printing of the
chart do not complete the problem of the chart maker. Both nature and
man are constantly changing the facts the representation of which has
been attempted on the charts, and also the needs of man are always
varying. The original surveys are made to meet the reasonable
requirements of the time, but breakwaters and jetties are built, and
channels and harbors dredged and otherwise improved, and cities built,
and new paths of commerce are opened which bring vessels into waters
previously thought of minor importance.
With the increase of commerce and speed of vessels more direct routes
are demanded for reasons of economy. Inside routes not originally used
are sometimes developed for defensive reasons. The average draft of the
larger vessels has also increased remarkably since the modern
hydrographic surveys were commenced, and surveys once made to insure
safety for the deepest vessels of that time are now not adequate. The
average loaded draft of the 20 largest steamships of the world has
increased as follows: 1848, 19 feet; 1873, 24 feet; 1898, 29 feet;
1903, 32 feet. The average length of these vessels was 230 feet in 1848,
390 feet in 1873, 541 feet in 1898, and 640 feet in 1903. The number of
vessels drawing as much as 26-1/4 feet rose from 36 in 1902 to 185 in
1904. In 1906 there were 17 vessels afloat, drawing 32 feet and upwards.
There are now two steamers on the Atlantic 790 feet long, 88 feet beam,
and 37-1/2 feet draft when fully loaded, and larger vessels are already
planned.
Great natural agencies are also constantly at work effecting changes in
features shown on the charts. The action of currents and waves is
continually cutting away or building the shore, particularly on sandy
coasts exposed to storms. When surveyed in 1849 Fishing Point on the
east coast of Maryland was but a bend in the shore line. By 1887 it had
built out about two miles in a southerly direction, and in 1902 about
two-thirds of a mile further, curving to the westward. Altogether in
about half a century this tongue of land has grown out nearly three
miles.
Rivers are bearing vast quantities of sediment and depositing these near
their mouths, pushing out the coast line and filling in the bottom. The
main mouths of the Mississippi are advancing into the Gulf, but at a
comparatively slow rate. A break from the main river at Cubit's Gap
just above the head of the passes, however, has done an enormous amount
of land making, filling in an area of about 50 square miles between 1852
and 1905.
[Illustration: FIG. 32. FISHING POINT, MARYLAND, FROM SURVEYS OF 1849
AND 1902, ILLUSTRATING BUILDING OUT OF A POINT ON THE COAST.]
[Illustration: FIG. 33. GROWTH OF LAND AT CUBITS GAP, MISSISSIPPI DELTA,
FROM 1852 to 1905.]
[Illustration: FIG. 34. COLUMBIA RIVER ENTRANCE, SHOWING MOVEMENT OF
SAND ISLAND, SURVEYS OF 1851, 1870 AND 1905.]
The mouth of the Columbia River in Oregon shows an interesting example
of the movement of an island. The chart of 1851 shows the center of Sand
Island 3-1/4 miles southeast of Cape Disappointment, the chart of 1870
shows it 2-3/4 miles southeast, and the chart of 1905 shows it 1-1/4
miles easterly. This island has thus moved 2 miles northwesterly
directly across the middle of the river entrance, closing up the former
north channel. The southern point of the entrance, Clatsop Spit, has
built out about the same distance.
[Illustration: FIG. 35. CHANGES IN HAULOVER BREAK, NANTUCKET ISLAND,
1890 TO 1903.]
[Illustration: FIG. 36. MAPS OF BOGOSLOF ISLAND, 1895 AND 1907, SHOWING
CHANGES DUE TO VOLCANIC ACTION.]
[Illustration:
_Photo by U. S. R. C. Service._
FIG. 37. BOGOSLOF VOLCANO, BERING SEA.]
Volcanic action in well authenticated cases has caused islands to rise
or disappear. In the present location of Bogoslof Island in Bering Sea
the early voyagers described a "sail rock." In this position in 1796
there arose a high island. In 1883 another island appeared near it. In
1906 a high cone arose between the two, and a continuous island was
formed over 1-1/2 miles long and 500 feet high. The latest report
(September, 1907) was that this central peak had suddenly collapsed and
disappeared. Bogoslof is an active volcano, and the main changes have
been the result of violent volcanic action. The history of this island
for over a century past forms a remarkable record of violent
transformations in the sea.
Earthquakes sometimes cause sudden displacements, horizontal or
vertical, of sufficient amount to affect the information shown on the
charts. A careful investigation of the effects of the earthquake in
Yakutat Bay, Alaska, in September, 1899, showed that the shore was
raised in some parts with a maximum uplift of 47 feet and depressed in
other parts, and that at least two reefs and four islets were raised in
the water area where none appeared before. Undoubtedly there were
changes in the water depths, but definite information is lacking because
there had been no previous hydrographic survey. The San Francisco
earthquake of 1906 caused little vertical displacement, but there were
horizontal changes of relative position as much as 16 feet; so far as
known this earthquake did not affect the practical accuracy of the
charts. Related to earthquake phenomena are the gradual coast movements
of elevation or subsidence which are taking place but at so slow a rate
as not to sensibly affect the charts in ordinary intervals of time.
Another agency at work is the coral polyp on the coral reefs; although
the rate of growth appears to be very slow, the resulting reefs and keys
are an important feature in tropical seas.
Practically all of the land features shown on charts are likewise
subject to changes, the more rapid of which are mainly due to the works
of man.
The changes of channels and of commercial needs cause many alterations
to be made from time to time in the lights and buoys which are shown on
the charts.
#Methods of correction.# The problem of keeping a chart sufficiently up
to date is one of much practical importance and one which must be taken
into account in planning what should be shown on the chart in the first
place so as to bring it within the range of practicable revision.
Certain features are corrected at once on the charts as soon as the
information is received, such as dangers reported, and changes in lights
and buoys. Where harbor works are in progress the periodic surveys made
in this country by the Corps of Engineers furnish data which are applied
promptly to the charts. Reported dangers in channels and bars are
investigated by special surveys and the information is put on the
charts. Examinations are made from time to time for the revision of the
features along the coast line. Complete resurveys have been made, at
long intervals, of some important portions of the coast where there has
been evidence of change, and these, when they become available, are
applied to the charts. All parts of the coast where the exposed portions
are not of very permanent material will require resurveys at intervals,
depending on their importance and the rate of change.
Notwithstanding the great progress made in hydrographic surveys, a
considerable number of rocks and shoals dangerous to navigation and not
previously shown on the charts are reported, averaging nearly 400 each
year for the last six years, according to the British reports. Of the
367 reported in 1906, 11 were discovered by vessels striking them.
Immediate information in the form of _Notices to Mariners_ is published,
of the more important corrections to charts which can be made by hand.
These corrections show what charts are affected, and give sufficient
data for plotting.
In the case of extensive corrections or new surveys a new edition of the
chart is printed and all existing copies of the previous edition are
canceled.
It is important that the user of the chart shall make certain that he
has the latest edition and that all corrections from its date of issue
have been applied from the _Notices to Mariners_.
It is unfortunately true that owing to failure to take proper account of
the notices, or to economy, old editions or unconnected charts are
sometimes used, and in a number of cases the loss of vessels has been
directly due to this cause. Those responsible for the safe navigation of
vessels should insist that the latest editions of charts are provided
and that all charts to be used are inspected and corrected to date.
READING AND USING CHARTS.
#Reading charts.# A chart is a representation on paper of hydrographic
and topographic information by means of various conventional methods and
symbols. It is evidently important for those making use of charts to
understand the system and conventions used, and to be able to interpret
readily the various parts of the chart. The ability to read a chart must
include an understanding of all its features, such as scale, projection,
geographic position, directions, depths, plane of reference, aids to
navigation, tides, currents, elevations, topography, and date of survey
and publication.
#Scale.# For American and British charts the scale is usually expressed
by the inches or fractions of an inch to the minute or degree of
latitude, or by the fractional proportion of a distance on the map to
the corresponding distance on the earth. These fractions are sometimes
stated on the British charts, and nearly always on those of the United
States Coast Survey. The chart catalogues give the scale in one or the
other form. A familiarity with the meaning of scales is of value in
selecting the most suitable chart, in judging of the relative uses of
charts, and in estimating distances. Where the fractional scales are
stated they furnish a simple means of comparing charts, as, for
instance, a chart on 1/50000 scale will show all distances just twice as
long as a chart on 1/100000 scale.
The following are scale equivalents:
Scale 1/10000 is equivalent to 7.30 inches to one nautical mile.
Scale 1/20000 is equivalent to 3.65 inches to one nautical mile.
Scale 1/40000 is equivalent to 1.82 inches to one nautical mile.
Scale 1/50000 is equivalent to 1.46 inches to one nautical mile.
Scale 1/80000 is equivalent to 0.91 inch to one nautical mile.
Scale 1/100000 is equivalent to 0.73 inch to one nautical mile.
Scale 1/200000 is equivalent to 0.36 inch to one nautical mile.
Scale 1/400000 is equivalent to 0.18 inch to one nautical mile.
Scale 1/1000000 is equivalent to 0.07 inch to one nautical mile.
Scale 1/1200000 is equivalent to 0.06 inch to one nautical mile.
For use in measuring distances on large scale charts the length of one
or more nautical miles is usually drawn on the chart, and sometimes
scales are also given in other units. On British charts the nautical
mile scale is divided into tenths (that is, cables of 100 fathoms or 600
feet length); on the American charts into quarters and eighths. Where
the scale covers more than one mile the fractional divisions are shown
only for the left-hand mile and the zero of the scale is placed between
this and the full mile scale, so that with dividers the full miles and
fraction may readily be taken off. The nautical mile in the United
States is taken to be the length of a minute of arc of a great circle on
a sphere whose surface equals that of the earth; this definition makes
the nautical mile equal 6080.27 feet. Lecky adopts 6080 feet as the
nautical mile. The length of the actual minute of latitude on the
earth's surface increases from 6046 feet at the equator to 6108 feet at
the poles, an increase of about one per cent. It is, however, this
somewhat variable unit of length which is ordinarily used in scaling
distances on the sailing charts.
On small scale charts there is usually a border scale entirely around
the chart, conveniently subdivided; this serves the double purpose of
facilitating the plotting or reading of positions by latitude and
longitude and of furnishing a scale of minutes of latitude for use in
measuring distances. On a mercator chart this scale of course varies
with the latitude and it must be referred to in the mean latitude of the
distance to be measured. In general practice the minute of latitude is
taken as equal to the nautical mile.
#Projection.# On only a few charts is there a statement of the
projection used. Practically all general sailing charts are on the
mercator projection, which can be readily recognized by the rectangular
network of meridians and parallels and the increase with latitude of the
distance between the parallels. On large scale local and harbor charts
the kind of projection used is not of importance to navigation, as for
such limited areas the difference between projections would not affect
the use of the chart. On certain small scale charts of the United States
Coast Survey which are on the polyconic projection this fact is stated
on the chart, and can also be readily recognized by the convergence of
the meridians and curvature of the parallels. Gnomonic charts intended
for taking off great circle courses are always described in their titles
and are also easily recognized by the increased scale and distortion
toward all the borders. Charts of the polar regions are published on
several different projections, which are distinguished from the mercator
by their circular or curved parallels.
#Geographic position.# For large scale and harbor charts the latitude
and longitude of some point marked on the chart are sometimes stated on
the face of the chart. For others of these, however, and for smaller
scale and general charts, positions are obtained by reference to the
border scale. There is a latitude scale down either side of the chart,
and a longitude scale across the top and bottom. These scales are
conveniently subdivided into degrees, minutes, or fractions of a minute.
The minute is divided into tenths (6´´), sixths (10´´), quarters (15´´),
or halves (30´´) on various charts.
#Directions# are indicated on charts both by the projection lines and by
compass roses. Nearly all charts are now oriented with the meridian,
that is, north is the top of the chart, and on a mercator chart the east
and west border lines are parallel with the meridians and the north and
south border lines with the parallels. Formerly many charts were not so
oriented. Some of these are still in use and can readily be recognized
by the diagonal or inclined direction of the projection lines with
respect to the border of the chart. Of course directions must not be
referred to the border lines of these diagonal charts, and scales along
such border lines must not be used. Directions with respect to true
north may always be referred to the projection lines of the chart, but
on a polyconic or polar chart a direction must not be carried so far
from any projection line as to introduce error on account of
convergence of the meridians. Compass roses are placed on charts to
facilitate the taking off or laying down of directions, though in some
respects their use is less accurate and convenient than the use of
protractors, referring to the projection lines. The British charts and
many of those of the United States Coast Survey have only magnetic
compasses, with degrees outside and points inside, the former graduated
to 90°. These are engraved on the chart with the magnetic variation for
the date of publication, or for a few years in advance, and give the
annual change in the variation. Because of expense of engraving they can
be changed on the charts only at intervals of some years, and until this
is done allowance for the change in variation is to be made if
important. The German charts and those of the United States Hydrographic
Office now have a threefold compass, the outer one degrees true, the
middle degrees magnetic and the inner points magnetic; the degrees in
both cases are graduated to 360°, reading from north through east,
south, and west; thus northwest would be stated as 315° instead of N.
45° W. Small scale charts covering extensive areas have no magnetic
compasses. They sometimes have true compasses, and usually have the
isogonic lines, or lines of equal magnetic variation, marked on them,
from which the variation at any intermediate point can be estimated.
#Depths.# The unit used for depths is always stated plainly on the
chart, and it is important to note this carefully, as the British,
American, and Japanese charts use fathoms for some charts and feet for
others, and most other countries use meters. Some of the earlier charts
of the United States coast have the depths inside of the 18-foot curve
in feet and outside of that curve in fathoms.
Depth curves are shown on charts in order to bring clearly to the eye
the different depth areas and the limits for navigation of vessels of
various drafts. The shoaler areas are usually indicated by sanding the
outer limit or the entire area within the depth curve. For the curves
of greater depths various standard symbols are used which vary slightly
in the different series but which may readily be recognized by the
soundings on either side of them. On the British charts the 1 and 3
fathom curves are usually indicated by sanding the outer edge of the
areas of these depths respectively; beyond these the standard curves
shown on these charts are the 5, 10, 20, and 100 fathom curves. Similar
curves are used on the United States charts. The German charts show the
2, 4, 6, 10, and 20 meter and various deeper curves, and the French the
2, 5, 10, and 20 meter and deeper curves. On the United States Lake
Survey charts the areas included within the 6, 12, and 18 foot curves
are shaded with a blue tint, heavy along the outer edge, which brings
out strongly the shoal areas.
Depth curves if clearly shown are a great aid in interpreting the
hydrography and making plain the shoals and passages. The system of
curves should always be understood when using a chart, and it may
sometimes aid the navigator to trace out with a pencil an additional
curve, if needed, beyond the draft of his vessel. The abbreviations used
for the bottom characteristics are explained either on the chart or on
the sheet of chart symbols, and give information which is useful in
anchoring, and may be helpful in identifying a position by soundings.
When a sounding is made without the lead reaching bottom, the depth
obtained is sometimes shown on the chart by a short line and zero above
the figure, indicating that at the depth stated, bottom was not obtained
(no bottom). There are a few important symbols shown in the water area
of charts. The sunken rock symbol indicates a dangerous area, or a
danger having a moderate depth of water over it, or a rock the least
water over which is not known; ordinarily on the United States charts
the least depth will be stated when known, and the symbol omitted. The
rock awash symbol indicates a rock awash at some stage of the tide,
unless more definitely stated. The position of a wreck is indicated by a
special symbol. P. D. (position doubtful) and E. D. (existence doubtful)
are placed after soundings or rocks or other features which depend on
some doubtful report not yet verified.
The following are the relations between depth units found on various
charts:
1 meter = 3.281 English feet = 0.547 English fathoms.
1 sajene (Russian) = 7 English feet = 1.167 English fathoms.
1 braza (old Spanish) = 5.484 English feet = 0.914 English fathom.
1.829 meters = 6 English feet = 1.000 English fathom.
#Aids to navigation.# Each series of charts has a definite system of
representing the aids to navigation; these are similar in principle but
differ as to detail. The characteristics of the lights, light-vessels,
buoys, and beacons are usually explained by abbreviations placed by the
side of each, and the entire system of representation is given on the
explanatory sheet for the charts. Various methods of coloring lights and
sectors and buoys are in use on different charts. It is evidently of
importance that the user of the chart should readily understand the
significance of the navigational aids as shown. For details regarding
lights it is of course desirable to refer to the light lists; for the
coasts of the United States detailed buoy lists are also published.
Range and channel lines when shown are represented by distinctive
symbols with bearings indicated. Danger ranges for the avoidance of
shoals are sometimes shown. On the British charts bearings as stated on
range and channel lines are magnetic; the custom varies on other charts
and must be carefully noted in each case.
#Plane of reference.# The soundings given on the chart express the depth
of water when the tide is at the height adopted for the plane of
reference; this same plane is used in the tide tables, which thus will
indicate the amount to be added to the soundings when the tide is above
the plane, or to be subtracted when it is below. In order to be on the
safe side the plane of reference adopted is always some low stage of the
tide, so that there is usually more water than shown on the chart.
On the British and German charts the soundings are reduced to the mean
low water of ordinary spring tides, unless otherwise stated. On the
charts of the Coast and Geodetic Survey the following are the planes of
reference: for the Atlantic and Gulf coasts, the mean of the low
waters; for the Pacific coast, Alaska, and the Philippines, the mean of
the lower low waters, except for Puget Sound and Wrangell Narrows, where
planes two and three feet lower respectively have been adopted.
According to the Tide Tables for 1908, at New York (Sandy Hook) the tide
will fall below the plane of reference on 135 days during the year, but
the extreme low tide will be only one foot below the plane. At Portland,
Maine, in 1908, the extreme low water is 2.1 feet below the plane, and
at San Francisco 1.5 feet. Of course when the tide is below the plane of
reference the amount must be subtracted from the depths shown on the
chart.
Strong winds and unusual barometric pressure may have a marked effect on
the height of tide, so that it may differ appreciably from the predicted
height, which is of course based on normal conditions. At Baltimore and
at Willets Point observation shows that a heavy wind may reduce the tide
four feet below the predicted heights.
#Tides.# Information regarding tides is given on all large scale charts,
and additional information and predictions may be found in the Tide
Tables. On the charts of the United States coast there is a small tide
table giving for the high and low waters the time relations to the
moon's transit and the height relations to the plane of reference. On
the British charts there is a brief statement as to the tides either
at the port on the chart or in the general notes; this ordinarily
gives the interval in hours and minutes between the moon's meridian
passage and the time of high water for the periods of full and new moon,
and also the amount in feet that the spring and neap tides rise above
the plane of reference, and the range of the neap tide. The following is
an example of such a tide note: "H. W. F. and C. Campbellton IV^h 0^m.
Springs rise 10 feet, Neaps 7 feet."
At some important ports information as to the state of the tide is given
to vessels, either by means of signal balls, or by automatic tidal
indicators, as at the Narrows in New York Harbor, where a large dial
shows to passing vessels the height of the tide, and an arrow indicates
whether it is rising or falling.
The tidal information becomes important and must be considered in
navigation or in anchoring in waters where the available depth at low
water approximates the draft of the vessel. In the general use of coast
charts it is also important to observe the effect of the stage of tide
on the appearance of many features. Rocks rising some feet above low
water may be entirely submerged at high water. In some areas the aspect
may be radically changed between high and low water by the baring of
extensive shoals or reefs.
#Currents.# Information, when available, as to currents is given either
by a note or by current arrows placed on the chart at the position of
observation. Additional information as to certain regions is given in
the United States Tide Tables. Tidal currents, flood and ebb, and
currents not due to tidal action are distinguished by symbols, and the
velocity is given in knots, and on some charts is indicated by the
lengths of the arrows.
Complete and systematic current observations have been made in
comparatively few localities because of the time and expense necessary
to get the full information as to the variations of the currents with
the tides and seasons. Ordinarily therefore the current arrows shown on
charts indicate only the average direction and velocity, or possibly
only the conditions existing at the season when the survey was made.
Oceanic and coast currents are probably much less uniform than might be
inferred from the current streams drawn on maps and charts. A more
systematic investigation of ocean currents is required to fulfill the
needs of navigation.
The tidal currents seldom turn with the tides, and there may be an
interval of as much as three hours between the time of high tide or
low tide and slack water. This leads to the apparent anomaly that in
cases the current may be running with its greatest velocity at the time
of high or low water, and may be running into a channel for several
hours after the tide commences to fall. It is therefore, evidently, not
safe to draw inferences as to currents solely from the tidal heights.
There are passages where the tidal currents become of the greatest
importance to navigation, as, for instance, in Seymour Narrows on the
inside route to Alaska, where the current velocity reaches 12 knots and
the interval of apparent slack water lasts but a few minutes.
#Elevations.# The unit used for elevations is also stated on the face of
the chart, as also the plane to which elevations are referred. On the
United States charts this is generally mean high water and on British
charts the high water of ordinary spring tides. Rocks and islets usually
have figures shown beside them, either in brackets or underscored, which
indicate the height above high water. Rocks which are bare at low water
sometimes have a note "dries" or "bares" so many feet, indicating their
height above low tide, although they are covered at high tide. The
British charts in some regions where there is a large range of tide have
underlined figures in the area between high water and low water
indicating the heights above low water, or the depths of water over the
bank at high water, as explained in each case.
#Topography.# The land area on most charts is distinguished from the
water area by a stipple or tint; on some charts the topographic features
have, however, been depended upon to bring out the land from the water.
The solid shore line is the high-water line, and should be clear on the
chart; the area between high and low water is sanded or otherwise shaded
on all charts. The relief of the land is represented by hill shading or
by contour lines which are the successive curves of elevation on the
land. Topographic symbols are used for some of the more important
features, such as cliffs, rocky ledges, buildings, bridges, trees,
roads, etc. It is important for the navigator to understand the
significance of the hill representation and the symbols, as they will
aid him in recognizing a coast or island, and in identifying landmarks.
#Date of survey and publication.# There is usually an authority note on
each chart showing the source of information or date of survey; if on a
coast subject to change, the latter is important. On the United States
Coast Survey charts the date of publication of the edition is given,
and on British and other charts the date of both large and small
corrections. The chart catalogues give the dates of the last editions,
or the dates of extensive corrections, and this affords a means of
seeing whether the copy of the chart in use is the latest edition
available.
USE OF CHARTS IN NAVIGATION.
#Chart working.# In crossing the open and deep portions of the ocean,
where the only data given may be the projection lines and soundings far
deeper than can be reached with navigational sounding machines, the
chart is used to lay out in advance the general course to be followed
and to plot the positions of the vessel at intervals either as
determined by observations or, lacking these, by dead reckoning. When
necessary the courses of the vessel are modified as the plotted
positions are found to fall one side or the other of the proposed
general track.
The principal operations on a chart are plotting or taking off positions
by latitude and longitude, laying down or taking off bearings,
directions, and courses, plotting or measuring distances, and laying
down or taking off angles.
To plot a position by its latitude and longitude on a mercator chart,
set a parallel ruler on the adjacent parallel and then move it to the
required latitude as shown by the border scale at either side; then with
a pair of dividers at the upper or lower longitude border scale take the
distance from the nearest meridian and lay this distance off along the
edge of the parallel ruler. The latitude and longitude of a point are
taken from the chart by reversing this process, or with the dividers
only. A direction is laid down on the chart or read from the chart
preferably by using some form of protractor and measuring the angle from
the projection lines. In this country it is more commonly done by
carrying the direction with a parallel ruler either from or to a compass
rose printed on the chart. Distances are measured or laid down on a
mercator chart by using the latitude border scale for the middle
latitude. On polyconic and other larger scale charts distances are
measured from the scales printed on the chart. It should be remarked
that in general where special accuracy is required distances should be
computed and not scaled from any chart, because of the error due to the
distortion of paper in printing.
The use of protractors on charts in plotting by angles in the
three-point problem will be referred to later.
The course to be steered to allow for a set due to current or wind may
be obtained by a graphical solution on the chart, though it will be
preferable to do this on other paper, using a larger scale. (Fig. 38.)
The direction and velocity of the set and the course and speed of the
ship may be considered as two sides of a parallelogram of forces, of
which the diagonal is the distance and course made good. To obtain the
course to steer to reach a given point with a given current and speed of
vessel, lay down the direction of the destination; from the starting
point lay off the direction of set and the amount in one hour; from the
extremity of this describe an arc with radius equal to the speed of the
vessel in one hour. A line drawn from the extremity of the direction of
set to the point of intersection of the arc and the course to be made
good will give the direction of the course to be steered, and the point
of intersection will also be the estimated position of the vessel at the
end of the hour's run.
#Methods of locating a vessel.# The principal methods used for locating
the position of a vessel are by astronomical observations, by dead
reckoning, by compass bearings, by ranges, by horizontal angles, by
soundings, by vertical angles, and by sound. The full discussion of
these methods pertains to navigation and pilotage, and they will be only
briefly referred to here as to their graphical application to charts.
#Astronomical methods.# There are a number of methods of obtaining the
position of a vessel by astronomical observations. When the position is
computed the chart enters into these only in the plotting of the final
result, so that with one exception these methods will not be referred to
further here.
The elegant method discovered by an American seaman, Captain Sumner, in
1843, is in part graphical, to be worked out upon the chart. This method
is based on the obvious fact that at any instant there is a point on the
earth having the sun in its zenith and which is the center of circles on
the earth's surface along the circumference of any one of which the
sun's altitude is the same at all points. A short portion of such a
circle may be considered as a straight line and can be determined by
locating one point and its direction, or two points in it. This is known
as a Sumner line. (Fig. 39.)
From an observation of the sun's altitude and azimuth and an assumed
latitude a position is computed and plotted and a line drawn on the
chart through this position at right angles to the azimuth of the sun as
taken from the azimuth tables and laid off from a meridian. Another
method is to compute positions with two assumed latitudes and plot the
two resulting positions and draw a line through them. The vessel must be
somewhere on the resulting Sumner line. A good determination may be
obtained by the intersection of two Sumner lines obtained from two
observations of the sun with sufficient interval so that there will be a
change of azimuth of as much as 30 degrees to give a fair intersection.
Allowance must be made for the movement of the vessel between the two
observations by drawing a line parallel to the first and at a distance
equal to the distance made good. An excellent intersection may be
obtained by observation of the sun, and before or after it of a star in
the twilight at a different azimuth.
[Illustration: COURSE TO ALLOW FOR SET, GRAPHICAL SOLUTION
FIG. 38.]
[Illustration: POSITION BY INTERSECTION OF SUMNER LINES
FIG. 39.]
[Illustration: POSITION BY COMPASS BEARINGS
FIG. 40.]
Even a single Sumner line, however, furnishes valuable information, as
it may be combined with other sources of information to obtain an
approximation to the position. The vessel must be somewhere on this
line, and this gives a good check on the position by dead reckoning, or
an intersection may be obtained with a line or bearing of a distant land
object, or a line of soundings may be compared on the chart with the
Sumner line.
If an observation is taken when the observed heavenly body is bearing
abeam, it is evident that the resulting Sumner line will be the
direction of the course of the vessel, and this fact may be useful in
shaping the course when nearing the land or a danger.
#Dead reckoning.# When impossible to obtain the position by any other
means, it is computed or plotted from the last determined position,
using the courses and distances run as shown by compass and log and
allowing for effect of current and wind. Because of uncertainties in all
these elements, positions so obtained may be from five to twenty miles
in error in a two-hundred-mile run, depending of course to some extent
on the speed of the vessel.
#Compass bearings.# A compass bearing of a single object, as a
lighthouse or a tangent to a point of land, laid down on the chart,
shows that the vessel is somewhere on that line, and when combined with
other information, as with a Sumner line or the course by dead reckoning
or the distance by a vertical angle, will give a position whose
correctness of course depends on the accuracy of the data used. Bearings
of two objects not in the same direction give two lines on the chart
whose intersection is the position. This will be very weak if the angle
of intersection is acute, and will become stronger as it approaches a
right angle. A bearing of a third object should be taken when
practicable, as it affords a valuable check in that the three lines
should intersect in the same point; if they do not do so when plotted
the error is either in the observations, or the compass, or the
plotting, or the chart. (Fig. 40). All compass bearings are of course
dependent upon the accuracy of the compass and the knowledge of its
errors due to the local magnetic effect of the ship, and also upon the
correctness with which the magnetic variation from true north is known.
Bearings of near objects should therefore always be preferred, and those
of distant objects considered as giving only approximate positions. An
error of one degree in the bearing of an object 30 miles away will
deflect the plotted line about one-half mile. Because of the facility
with which they may be taken compass bearings are much used for inshore
navigation, but in point of reliability they are inferior to some of the
other methods.
A single or "danger" bearing of an object is often a valuable guide in
avoiding a danger. For example, a reef may lie to the westward of a line
drawn South 10° East from a lighthouse; in approaching a vessel will
pass safely to the eastward of the reef if the lighthouse is not allowed
to bear any to the northward of North 10° West. (Fig. 41.)
Two successive bearings of a single object, as, for instance, a
lighthouse, noting the distance run in the interval, afford a convenient
and much used means of locating the position with respect to that
object. Such bearings are drawn on the chart in reversed direction from
the object. The distance run between the bearings, as read by the log
and corrected for current if practicable, is scaled off with dividers
and the course of the vessel is set off with parallel ruler; the latter
is then moved across the two plotted directions until the distance
intercepted between them equals that scaled with the dividers, and the
edge of the ruler then represents the track of the vessel. (Fig. 42.) If
the angle from the bow, or from the course of the vessel, for the second
bearing is double that for the first bearing, the distance from the
object at the second bearing is equal to that run by the vessel in the
interval, and the use of this simple relation is designated as "doubling
the angle on the bow." If the angles between the course and the object
are respectively 45° and 90° when the two bearings are taken on an
object on the shore, the distance that the ship passes offshore when the
object is abeam is equal to the distance run between the two bearings;
this is a much used navigational device, known as the "bow and beam
bearing" or the "four-point bearing." There is an advantage, however, in
using bearings at two and four points (or 22.5° and 45°), as these give
the probable distance that the object will be passed before it is abeam.
#Ranges.# A valuable line of position is obtained by noting when two
well-situated objects are in range, that is, one back of the other in
the line of sight from the vessel, as, for instance, a church spire
appearing behind a lighthouse or a rock in line with a prominent point.
Such ranges are of course entirely free from compass errors, and should
be noted whenever there is favorable opportunity. The value of the range
in plotting will increase with the distance between the objects, and if
the two are close in proportion to the distance to the vessel the
direction will be weak owing to the uncertainty in drawing a direction
through close points. Artificial ranges are often erected as aids to
navigation, usually to indicate the course to be followed in passing
through a channel. Ranges afford a valuable guide in avoiding dangers,
as for example an inspection of the chart may show that if a certain
lighthouse is kept in line with or open from an islet a dangerous shoal
will be given a good berth; on coasts not well buoyed such danger ranges
are sometimes marked on the charts. (Fig. 43.)
[Illustration: DANGER BEARING
FIG. 41.]
[Illustration: POSITION BY SUCCESSIVE BEARINGS TWO AND FOUR POINT
BEARINGS
FIG. 42.]
[Illustration: RANGE TO AVOID DANGER
FIG. 43.]
#Horizontal sextant angles.# The location of a position by the
three-point problem, using sextant angles, is much more exact than by
bearings, but is less used because not so well known and also because
additional instruments are required and the conditions are not always
favorable. It is so valuable a method, however, that it should be used,
when necessary, on every well-equipped vessel. A single horizontal angle
taken with a sextant between objects, as two lighthouses, defines the
position of the vessel as somewhere on the circumference of a circle
passing through the two objects and the vessel. A protractor laid on the
chart with two of its arms set at the observed angle and passing through
the two objects, will permit of locating two or more points of this
circle on the chart. This furnishes a line of position which may be
combined with other information to locate the vessel. With a compass
bearing of one of the objects the position may be plotted directly from
the single angle. Two sextant angles measured at the same instant
between three objects furnish one of the most accurate means of locating
the position of a vessel, this being the same method that is ordinarily
used in hydrographic surveying, known as the three-point problem. (Fig.
44.) The two angles are conveniently set off on a three-arm protractor,
which is shifted on the chart until the three arms touch the three
points, when the position of the center is plotted. A third angle to a
fourth point furnishes a valuable check in case of doubt. Two angles may
also be taken to four objects without any common point, and in this case
portions of the two circles of position are plotted and their
intersection will be the ship's position.
The value of this method depends largely on the selection of favorably
located objects, and it is quite important that the principles of the
three-point problem be understood. If the ship is on or near the
circumference of a circle which passes through the three objects the
position will be very weak, and the same is true if the distance between
any two of the objects is small as compared with the distance from them
to the vessel. A useful general rule is that the position will be strong
if the middle one of the three objects is the nearest to the vessel,
provided that no two of the objects are close together in comparison
with the distance to the vessel.
A single sextant angle furnishes a means of avoiding a known danger by
using what is known as the horizontal "danger angle." (Fig. 45.) Note
two well-defined objects on the coast either side of the danger to be
avoided and describe a circle through them and passing sufficiently
outside of the reef to give it a safe berth. With a protractor on the
chart note the angle between the objects at any point on the outer part
of this circle. If in passing, the angle at the ship between the two
objects is not allowed to become greater than this "danger angle" the
danger will be given a sufficient berth. This method as well as any use
of sextant angles or bearings depends of course on the accuracy of the
chart, and caution must be used where it is not certain that the chart
depends upon an accurate survey.
[Illustration: POSITION BY SEXTANT ANGLES THREE POINT PROBLEM
FIG. 44.]
[Illustration: HORIZONTAL DANGER ANGLE
FIG. 45.]
[Illustration: DISTANCE BY VERTICAL ANGLE]
[Illustration: VERTICAL DANGER ANGLE
FIG. 46.]
#Soundings.# Even if objects cannot be seen, due to distance or thick
weather, the chart furnishes a valuable aid when a vessel has approached
within the limits where it is practicable to obtain soundings. Modern
navigational sounding machines permit of obtaining soundings to depths
of nearly one hundred fathoms without stopping the vessel. A rough check
is at once obtained by comparing such soundings with those given on the
chart for the position carried forward by dead reckoning. If a number of
soundings are taken and plotted on a piece of tracing paper, spaced by
the log readings to the scale of the chart, and this tracing paper is
laid over the chart and shifted in the vicinity of the probable position
until the soundings best agree with those on the chart, a valuable
verification of position may be obtained. This is particularly the case
if the area has been well surveyed, and the soundings taken on the
vessel are accurate, and the configuration of the bottom has marked
characteristics. For instance, in approaching New York the crossing of
the 30, 20, and 10 fathom curves will give a fair warning of the
distance off the Long Island and New Jersey coasts, and soundings across
such a feature as the submerged Hudson gorge extending to the
southeastward of Sandy Hook will give a valuable indication of position.
The taking of soundings should be resorted to even in favorable
conditions, in approaching shoal water, as a check on other means of
locating the vessel. Many marine disasters are attributed to failure to
make sufficient use of the lead, the simplest of navigational aids.
#Vertical angles.# The vertical angle of elevation of an object whose
height is known will give the distance, and combined with a bearing or
other information this permits of locating a vessel where better means
cannot be used. Distance tables are published for this method. (Fig.
46.) The vertical angle is measured with a sextant and must be the angle
at the ship between the top of the object and the sea level vertically
beneath it; for a hill or mountain, therefore, the eye of the observer
should be near the water. The object should not be so distant that
curvature becomes appreciable. The "vertical danger angle" is a means of
avoiding a known danger, on a principle similar to that of the
horizontal danger angle; that is, the angle of elevation of a known
object is not permitted to become greater than a fixed amount depending
on the distance from the object to the danger to be avoided.
#Positions by sound.# In thick weather sound affords a valuable aid to
the navigator. In narrow passages noting the echo of the whistle from a
cliff is a method resorted to, as for instance in Puget Sound and along
the Alaska coast. Fog whistles and bell buoys are maintained at many
places. Submarine bells have recently been introduced at a number of
points along the Atlantic coast, and vessels may be equipped to receive
these submarine signals transmitted through the water, which indicate
also the general direction from which the sound comes.
#Need of vigilance.# Too great importance cannot be attached to frequent
verification of positions by the best available means, particularly when
approaching the land. Neglect of this or overconfidence has caused many
disasters. A notable instance was the loss of one of the largest Pacific
steamers on the coast of Japan in March, 1907. In the afternoon of a
clear day this vessel ran on to a well-known reef about a mile from a
lighthouse, resulting in the total loss of vessel and cargo valued at
three and a half million dollars. The captain was so confident of his
position and that he was giving the reef a sufficient berth that he laid
down no bearings on the chart and took no soundings.
[Illustration: FIG. 47. FIELD'S PROTRACTOR AND PARALLEL RULER IN USE ON
A CHART, PLOTTING BEARING OF A LIGHTHOUSE.]
#Instruments.# The principal instruments needed for use with charts are;
dividers for taking off distances and latitudes and longitudes, parallel
ruler for transferring directions to or from a compass rose and for
taking off or plotting the latitude on a mercator chart, protractor of
180 degrees for reading the angle with the meridian of any direction or
for laying off on the chart any given angle with the meridian, and
three-arm or other full-circle protractor for plotting a position by the
three-point problem.
Parallel rulers on the principle of Field's are strongly recommended for
chart work, as they combine in a single instrument the advantages of a
parallel ruler and a 180-degree protractor. Any direction can be read or
laid off by simply moving the parallel ruler to the nearest projection
line, which is a process not only more convenient than referring to the
compass rose printed on the chart but also more accurate because of the
longer radius. These instruments can also be used the same as a plain
parallel ruler. Field's parallel rulers are made in two forms, one
rolling and the other sliding. The former is a single ruler with edge
graduated 90 degrees either way, and mounted on rollers; it is the most
rapid instrument for reading or laying off a direction, but it requires
a smooth surface. The latter is an ordinary two-bar parallel ruler with
edge when closed graduated 90 degrees either way; it is a very
serviceable instrument and probably more to be depended upon for
ordinary use than the rolling form. Some form of combined protractor and
parallel ruler should be in every navigational equipment, and it is
unfortunate that these instruments are not better known in this country.
There are other forms of half-circle protractors which are used on the
same principle, that is, of bringing the center on to a projection line
and reading where the line cuts the border graduation of the protractor.
Thus a semicircular protractor is used with a separate straight edge,
along which it is slid to the nearest meridian; another form is the
simple circular protractor with a thread fastened at the center. All
these forms of protractors, it will be noted, are intended to work from
the true meridian, and they are usually graduated in degrees only; the
use of degrees instead of points is becoming much more general in
navigational work, and reference to the true meridian is also more
common than formerly.
The standard three-arm protractor, or station pointer, as it is known to
the English, should be a part of every navigational outfit because of
its value in locating a position by the three-point problem. A recent
American invention, Court's three-arm protractor, is an instrument made
of celluloid for the same purpose. It should not be considered as a
substitute for the standard metal instrument, but it is a simple, cheap,
and handy supplement to it, as it may be readily used for small angles
and short distances where there are mechanical difficulties in working
with the metal three-arm protractor. Other protractors can be used for
the three-point problem, as, for instance, Cust's protractor on
celluloid, on which the angles are drawn in pencil and erased, and the
tracing-paper protractor.
#Degree of reliance on charts.# The value of a chart must not be judged
alone from its general appearance, as skill in preparation and
publication may give a handsome appearance to an incomplete survey. On
the other hand a thorough survey might through poor preparation result
in a chart defective either in information or in utility.
[Illustration: FIG. 48. THREE-ARM PROTRACTOR IN USE ON A CHART, PLOTTING
POSITION FROM TWO ANGLES.]
The degree of completeness of the soundings, the character of the
region, and the date of the survey should be taken into account in
deciding as to the amount of reliance to be placed on the chart. Areas
where the soundings are not distributed with fair uniformity may be
assumed not to have been completely surveyed. Caution should be used in
navigating on charts where the survey is not complete, and even where
careful surveys exist care must be taken if the bottom is of very
irregular nature with lumps near the navigable depth, as for instance on
some of the coral reef coasts. Isolated soundings shoaler than the
surrounding depths should be avoided, as there may be less water than
shown. In such a region, unless the whole area is dragged, it is
impossible to make it entirely certain that all obstructions are
charted.
While an immense amount of faithful work has been put into the
preparation of many charts, the user must constantly exercise his own
judgment as to the reliance to be placed on them. A coast is not to be
considered as clear unless it is shown to be; buoys may get adrift and
be in a different position or be gone altogether; fog signals vary in
distinctness owing to atmospheric conditions; extreme or unusual tides
may fall below the plane of reference; owing to strong winds the actual
tide may differ from the predicted tide. Errors sometimes creep in from
various sources, such as those due to different reference longitudes or
the use of a corrected longitude for a portion of the chart without
changing other positions to which the same correction is applicable;
clerical and printing errors may occur; there are sometimes omissions in
surveys; a feature may get plotted in two different positions; tide rips
are reported as breakers and floating objects as rocks or islands, and
thus many dangers have gotten on the charts which cannot be found again,
and false reports are sometimes made to shield some one from blame. Most
of these classes of errors and uncertainties, however, disappear in the
use of charts of a thoroughly surveyed coast.
#Use the latest editions of charts.# The latest edition of a chart
should always be used and should be corrected for all notices since its
issue. Carelessness or false economy in not providing the largest scale
or the latest chart has been the cause of more than one marine disaster.
The British Board of Trade issue the following official notice to
shipowners and agents: "The attention of the Board of Trade has
frequently been called to cases in which British vessels have been
endangered or wrecked through the masters' attempting to navigate them
by means of antiquated or otherwise defective charts. The Board of Trade
desires, therefore, to direct the especial attention of shipowners and
their agents to the necessity of seeing that the charts taken or sent on
board their ships are corrected to the time of sailing. Neglect to
supply a ship with proper charts will be brought prominently before the
Court of Inquiry in the event of a wreck occurring from that cause."
The following is a translation of a notice in the preface to the
catalogue of charts published by the German government: "Owners and
masters of vessels are apprised that cases of marine accidents in which
the casualty was due to antiquated or erroneous charts, have frequently
been before the admiralty courts. In consequence of this, the
'Instructions for the prevention of accidents to steamers and sailing
vessels,' issued by the Seeberufsgenossenschaft have been amended by the
following additional paragraph: 'It is obligatory upon every master,
except when engaged in local coastwise navigation, to keep the Notices
to Mariners regularly, and with the aid of them to carefully keep his
charts up to date.'"
The British shipping laws provide that a ship may not be sent to sea in
such an unseaworthy state that the life of any person is thereby
endangered, and the House of Lords has defined the term "seaworthy" to
mean "in a fit state as to repairs, equipment, and crew, and in all
other respects, to encounter the ordinary perils of the voyage." Proper
charts and sailing directions are a necessary part of the equipment of a
vessel, and the courts have frequently inquired into this.
The records of the British courts, however, show that even in recent
years many ships have been damaged or lost owing directly or indirectly
to failure to have the latest information on board. The following are
instances from these records.
In 1890 the steamer _Dunluce_ was lost owing to the use of an old
edition of the Admiralty chart which showed a depth of 4-1/2 fathoms on
the Wikesgrund, whereas the later chart showed much less water. In this
case the master had requested his ship chandler to send him the latest
chart.
In 1891 the steamer _St. Donats_ got ashore on a patch which was not
shown on the chart in use, which was privately published in 1881; the
danger was, however, shown on the Admiralty chart corrected to 1889.
Also in 1891 the steamer _Trent_ was lost on the Missipezza Rock in the
Adriatic. The ship was navigated by a private chart published in 1890
which did not show this rock, and by sailing directions published in
1866.
The steamer _Aboraca_, stranded in the Gulf of Bothnia in 1894, was
being navigated by a chart corrected to 1881 which did not show that the
Storkallagrund light-vessel had been moved eight miles.
The steamer _Ravenspur_ was lost on Bilbao Breakwater owing to the use
of a chart not up to date which did not show the breakwater. In 1898 the
steamer _Cromarty_ was lost in attempting to enter Ponta Delgada harbor,
and in 1901 the steamer "Dinnington" was lost by steaming on to the new
breakwater in Portland harbor; both of these disasters were likewise due
to the use of old charts which did not show the breakwaters. In these
three cases the masters of the vessels had authority to obtain the
necessary charts at the owners' expense.
Not so, however, in the following case from the finding of a British
marine court in 1877: "The primary cause of the ship's getting on shore
was due to the master's being guided in his navigation by an obsolete
Admiralty chart dated September 1, 1852, and corrected to April, 1862,
and on which no lights are shown to exist either in ... or ... and to
his not being supplied with the latest sailing directions. The Court,
considering that the master was obliged to furnish himself with
chronometer, barometer, sextant, charts, sailing directions, and
everything necessary for the navigation of his vessel out of his private
resources, which, under very favorable circumstances, might perhaps
reach £150 a year, find themselves unable in this instance to pass a
heavier censure upon him than that he be severely reprimanded."
The loss of the German steamer _Baker_ on the coast of Cuba on January
31, 1908, was declared by the marine court at Hamburg to be due in part
to the use of an unofficial chart which did not show the latest surveys
on that coast.
#Use the largest scale charts.# The largest scale chart available should
be employed when entering channels, bays, or harbors, as it gives
information with more clearness and detail, positions may be more
accurately plotted, and sometimes it is the first corrected for new
information.
The records of the courts of inquiry also show cases where vessels have
been wrecked owing to the use of charts of too small scale.
In 1890 the steamer _Lady Ailsa_ was lost on the Plateau du Four. The
only chart on board for this locality was a general chart of the Bay of
Biscay, and the stranding was due to the master's mistaking one buoy for
another. The court found that the chart, although a proper one for
general use, was not sufficient for the navigation of a vessel in such
narrow waters and on such a dangerous coast.
The _Zenobia_ was stranded on the San Thomé Bank in 1891. On this vessel
the owners were to furnish the chronometers and the master the charts
and sailing directions. The master was, however, apparently satisfied
with only a general chart of the South Atlantic for navigation on the
coast of Brazil, and had no sailing directions at all.
#The depth curves# on charts furnish a valuable guide, and if the curves
are lacking or broken in some parts it is usually a sign that the
information is incomplete. The 100-fathom curve is a general warning of
approach to the coast. The 10-fathom curve on rocky coasts should be
considered as a danger curve, and caution used after crossing it. The
5-fathom curve is the most important for modern vessels of medium draft,
as it indicates for them the practical limit of navigation. The 3, 2,
and 1-fathom curves are a guide to smaller vessels, but have less
significance than formerly because of the increase of draft of vessels.
#The shrinkage of paper#, especially in plate printing, has been
referred to. This introduces two possible sources of error: first, the
shrinkage being different in the two directions, any scale printed on
the chart will be accurate only when used in a direction parallel to
itself; second, for the same reason, angles and directions will be
somewhat distorted. Fortunately these errors are not serious in the
ordinary navigational use of a chart, but they should not be overlooked
when accurate plotting or measuring of distances is attempted on a
plate-printed chart.
The actual shrinkage measured on charts printed from plates varies from
1/3 inch to 1 inch in a length of chart of 36 inches. On British and
American plate printed charts the shrinkage is usually from two to
nearly three times as much in one direction as it is in the other.
#Care of charts.# In order that they may be properly used charts should
be filed flat and not rolled. They should be systematically arranged so
that the desired chart can be instantly found. They should be cared for
and when in bad condition replaced by new copies. They can be most
conveniently filed in shallow drawers, thus avoiding the placing of many
charts in a single drawer. The latter is a common fault; it not only
increases the labor of handling the charts but adds to the liability of
their injury.
PUBLICATIONS SUPPLEMENTING NAUTICAL CHARTS.
There are several publications in book and in chart form which are
either necessary or convenient for use in connection with nautical
charts. These comprise the coast pilots, notices to mariners, tide
tables, light and buoy lists, and various special charts.
#Coast pilots#, or sailing directions, are books giving descriptions of
the main features, as far as of interest to seamen, of the coast and
adjacent waters, with directions for navigation. They contain much
miscellaneous information of value to the mariner, especially the
stranger. Although they contain additional facts which cannot be shown
on the charts, they are not at all intended to supersede the latter; the
mariner should in general rely on the charts. The sailing directions can
be less readily corrected than the charts, and in all cases where they
differ the charts are to be taken as the guide.
The most extensive series of sailing directions is that published by the
British Admiralty, comprising fifty-six volumes and including all the
navigable regions of the world. In the United States the Coast and
Geodetic Survey publishes ten volumes of coast pilots for the Atlantic,
Gulf, and Pacific coasts, Porto Rico, and southeastern Alaska, and eight
volumes of sailing directions for Alaska and the Philippine Islands. The
United States Hydrographic Office publishes sixteen volumes of sailing
directions for various parts of the world.
#Notices to Mariners# are published at frequent intervals, giving all
important corrections, which should be at once applied by hand to the
charts, such as rocks or shoals discovered and lights and buoys
established or moved. New charts, new editions, and canceled charts are
also announced.
These notices should be carefully examined and the necessary corrections
made on all charts of the sets in use on the vessel. A chart should be
considered as a growing rather than a finished instrument, and constant
watchfulness is required to see that it is kept up to date. Neglect of
this may cause shipwreck, as the following instance shows. Report came
to Manila in 1904 that there was a low sand islet lying off the very
poorly charted northeast coast of Samar; this information was promptly
published in the local Notice to Mariners. About a month later a small
steamer was sent to land some native constabulary on that coast. The
captain failed to obtain or observe this notice, and approached the
coast before daylight on a course which led directly across the sand
islet. The vessel was driven far up on the sand, where it still lies.
In the United States, weekly Notices to Mariners are published by the
Department of Commerce and Labor for the coasts under the jurisdiction
of the United States, and by the Navy Department for all regions. These
notices are distributed free and can be obtained from chart agents and
consular officers. In Great Britain the notices are published at
frequent intervals by the Hydrographic Office, and practically all
countries issuing charts also issue such notices. Information as to
important changes in lights and other announcements of navigational
interest are also sometimes printed in the marine columns of newspapers
and in nautical periodicals.
#Tide Tables.# Brief information as to the time and height of the tide
is usually for convenience given on the face of the chart. More complete
information is published in the Tide Tables, with which every navigator
should be provided. "The Tide Tables for United States and foreign
ports," published annually in advance by the United States Coast and
Geodetic Survey, give complete predictions of the time and height of
high and low water for each day of the year for 70 of the principal
ports of the world, and the tidal differences from some principal port
for 3000 subordinate ports. The other leading nations also publish
annual tide tables; those of the British government are entitled "Tide
Tables for British and Irish ports, and also the times of high water for
the principal places on the globe."
#Light and buoy lists.# Brief information as to all artificial aids to
navigation is shown on the charts. Every vessel should also have on
board the latest official light and buoy lists, which give a more
detailed description than can be placed on the charts.
Light and buoy lists for the coasts of the United States are published
annually by the Light-House Board. The United States Hydrographic Office
publishes a "List of Lights of the World" (excepting the United States),
in three volumes.
The British Hydrographic Office publishes eight volumes of Lists of
Lights, and these are corrected annually.
#Chart catalogues# are published in connection with all series of
charts. They give the particulars and price of each chart published, and
are usually arranged in geographical order, with both alphabetical and
numerical indexes, for convenience in finding charts either by position,
name, or number.
#Charts for special purposes.# There are various special charts
published for the benefit of mariners, although not intended for direct
use in plotting the course of a vessel or in locating its position. Some
of the more important of these are mentioned below.
#Gnomonic charts# are intended solely for laying down the great circle
or shortest practicable courses between points, for which purpose they
are very convenient. Their use has already been described. The United
States Hydrographic Office publishes six such charts, for the North
Atlantic, South Atlantic, Pacific, North Pacific, South Pacific, and
Indian Oceans.
#Current charts# are published by the British Hydrographic Office for
the various oceans; these usually show the average ocean currents, but
for the Atlantic there are monthly and for the Pacific quarterly current
charts.
#Magnetic variation charts# are published by both the United States and
British governments. They show on a mercator chart of the world the
isogonic lines, or lines along which the variation of the needle from
true north is the same. The lines are drawn for each degree of
variation. The annual change in the variation is also indicated.
Other magnetic charts are published showing the lines of equal magnetic
dip, horizontal magnetic force, and vertical magnetic force.
#Meteorological ocean charts# are published by several governments,
including the United States, Great Britain, and Germany, and give the
average weather conditions, winds, fogs, currents, ice, tracks of
storms, and other information. "Pilot charts" of the North Atlantic and
North Pacific Oceans are issued by the United States Hydrographic Office
about the first of each month, and give "a forecast of the weather for
the ensuing and a review of that for the preceding month, together with
all obtainable information as to the most available sailing and steam
routes, dangers to navigation, ice, fog, derelicts, etc., and any
additional information that may be received of value to navigation."
Mariners in all parts of the world have joined in contributing the
information which has been used in compiling these pilot charts.
#Track charts# are published by the British and United States
governments. That of the latter is entitled "Track and distance chart of
the world, showing the routes traversed by full-powered steamers between
the principal ports of the world, and the corresponding distances."
#Telegraph charts# are published showing the "telegraphic connections
afforded by the submarine cables and the principal overland telegraph
lines."
#Index charts# are outline plans showing the area covered by each chart
of a series, and furnish a convenient means of finding a chart of any
desired region or of selecting the most suitable chart for any purpose.
These index charts are published either in sets, showing all the charts
of a series, or are bound into the chart catalogues.
#Star charts# are included in navigational series, and are conveniently
arranged for use on shipboard in identifying the brighter stars. The
United States Hydrographic Office publishes two, constellations of the
northern and of the southern hemispheres.
#Explanatory sheets# are published in connection with various series of
charts, giving explanations of the symbols and abbreviations used and of
other important features. In the United States the Coast and Geodetic
Survey has issued a small pamphlet, "Notes on the use of charts," which
contains explanations of its chart symbols, and the Hydrographic Office
has published "A manual of conventional symbols and abbreviations in use
on the official charts of the principal maritime nations."
INDEX
PAGE
Aids to navigation, 118
Arbitrary projection, 79
Astronomical observations, 32
Astronomical positions, 126
Bearings, position by, 130
Board of Trade notice, 148
Care of charts, 153
Catalogues of charts, 157
Changes in the coast, 98
Chart making, development of, 6
Chart publications of various nations, 18
Charts, earliest nautical, 6
Charts, loxodromic, 7
Charts, plain, 8
Chart schemes, 67
Chart working, 124
Coast and Geodetic Survey, United States, 13
Coast pilots, 154
Compass bearings, 130
Compass, nautical use of, 6
Compass, variation of, 7
Compilation of information, 67
Correction of charts, method of, 110
Cosa, Juan de la, 8
Current charts, 157
Currents, 50, 121
Danger angle, horizontal, 136
Danger bearing, 131
Danger range, 132
Dangers, reports of, 56
Dates on charts, 123
Dead reckoning, 129
Depth curves, 116, 152
Depths, unit for, 19, 116
Depth units, relation of, 118
Directions on charts, 115
Distances, measured on chart, 125
Distribution of charts, 96
Doubling angle on bow, 131
Draft of vessels, 97
Dragging for dangers, 55
Earthquakes, 109
Electrotyping plates, 89
Elevations, 122
Engraving machines, 89
Engraving on copper, 84
Engraving on stone, 93
Eskimo map, 1
Etching on copper, 95
Explanatory sheets, 159
Flattening of the earth, 3
France, establishment of chart office, 10
Geographic position on charts, 115
Geography, early, 2
Germany, contributions to hydrography, 14
Gnomonic charts, 79, 157
Gnomonic projection, 74
Great Britain, contributions to geography, 14
Holland, development of chart making, 10
Hydrographic Office, British, 13
Hydrographic Office, United States, 13
Hydrography, 40
Index charts, 158
Information on charts, 23
Instruments used on charts, 141
Lake Survey, United States, 13
Largest scale chart, 151
Latest editions of charts, 148
Light and buoy lists, 156
Lithographic printing, 94
Locating a vessel, 126
Longitude, initial, 19
Longitude, uncertainties in, 10
Magnetic charts, 157
Magnetic variation, 56
Map, earliest, 2
Map making, development of, 2
Maps, need of, 1
Maritime surveys, extension of, 17
Mercator chart, history, 8
Mercator projection, 68
Meteorological charts (pilot charts), 158
Navigation, use of charts in, 124
Notices to mariners, 111, 155
Paper, shrinkage of, 152
Parallel rulers, Field's, 141
Photolithography, 93
Plane of reference, 20, 119
Plotting positions, 124
Polyconic projection, 73
Printing, plate, 84, 90
Privately published charts, 21
Progress of hydrographic surveys, 17
Projection, explanation of, 114
Projections, 68, 114
Protractor, three-arm, 144
Ptolemy, 3
Publication of charts, methods, 84
Purpose of charts, 22
Ranges, 132
Reading charts, 112
Reliance on charts, 144
Reports of dangers, erroneous, 57
Requirements for charts, 23
Revision of charts, need of, 97
Rock, Brooklyn, 50
Sailing directions, early, 4
Sailing directions, 154
Scale equivalents, 113
Scales of charts, 79, 112
Set, graphical allowance for, 125
Sextant angles, 132
Sheets for surveys, 39
Shrinkage of paper, 152
Sound, position by, 140
Sounding machines, 49
Soundings, position by, 136
Star charts, 159
Station pointer, 144
Steamer for surveying, 49
Sumner's method, 126
Supplementary publications, 154
Surveys on foreign coasts, 14
Surveys, need of thorough, 31
Symbols on charts, 20
Telegraph charts, 158
Three-point problem, 132, 135
Tides, 50, 120
Tide tables, 156
Topography, 39
Topography on charts, 123
Track charts, 158
Triangulation, 32
Uniformity in charts, 21
Use of charts in navigation, 124
Vertical angles, 139
Vigias, removal of, 62
Vigilance, need of, 140
Volcanic action, 109
Wrecks due to deficient charts, 149
SHORT-TITLE CATALOGUE
OF THE
PUBLICATIONS
OF
JOHN WILEY & SONS,
NEW YORK.
LONDON: CHAPMAN & HALL, LIMITED.
ARRANGED UNDER SUBJECTS.
Descriptive circulars sent on application. Books marked with an asterisk
(*) are sold at _net_ prices only. All books are bound in cloth unless
otherwise stated.
AGRICULTURE.
Armsby's Manual of Cattle-feeding. 12mo, $1 75
Principles of Animal Nutrition. 8vo, 4 00
Budd and Hansen's American Horticultural Manual:
Part I. Propagation, Culture, and Improvement. 12mo, 1 50
Part II. Systematic Pomology. 12mo, 1 50
Elliott's Engineering for Land Drainage. 12mo, 1 50
Practical Farm Drainage. 12mo, 1 00
Graves's Forest Mensuration. 8vo, 4 00
Green's Principles of American Forestry. 12mo, 1 50
Grotenfelt's Principles of Modern Dairy Practice. (Woll.) 12mo, 2 00
Hanausek's Microscopy of Technical Products. (Winton.) 8vo, 5 00
Herrick's Denatured or Industrial Alcohol. 8vo, 4 00
Maynard's Landscape Gardening as Applied to Home Decoration. 12mo, 1 50
* McKay and Larsen's Principles and Practice of
Butter-making. 8vo, 1 50
Sanderson's Insects Injurious to Staple Crops. 12mo, 1 50
* Schwarz's Longleaf Pine in Virgin Forest. 12mo, 1 25
Stockbridge's Rocks and Soils. 8vo, 2 50
Winton's Microscopy of Vegetable Foods. 8vo, 7 50
Woll's Handbook for Farmers and Dairymen. 16mo, 1 50
ARCHITECTURE.
Baldwin's Steam Heating for Buildings. 12mo, 2 50
Bashore's Sanitation of a Country House. 12mo, 1 00
Berg's Buildings and Structures of American Railroads. 4to, 5 00
Birkmire's Planning and Construction of American Theatres. 8vo, 3 00
Architectural Iron and Steel. 8vo, 3 50
Compound Rivetée Girders as Applied in Buildings. 8vo, 2 00
Planning and Construction of High Office Buildings. 8vo, 3 50
Skeleton Construction in Buildings. 8vo, 3 00
Brigg's Modern American School Buildings. 8vo, 4 00
Carpenter's Heating and Ventilating of Buildings. 8vo, 4 00
Freitag's Architectural Engineering. 8vo, 3 50
Fireproofing of Steel Buildings. 8vo, 2 50
French and Ives's Stereotomy. 8vo, 2 50
Gerhard's Guide to Sanitary House-inspection. 16mo, 1 00
Sanitation of Public Buildings. 12mo, 1 50
Theatre Fires and Panics. 12mo, 1 50
* Greene's Structural Mechanics. 8vo, 2 50
Holly's Carpenters' and Joiners' Handbook. 18mo, 75
Johnson's Statics by Algebraic and Graphic Methods. 8vo, 2 00
Kellaway's How to Lay Out Suburban Home Grounds. 8vo, 2 00
Kidder's Architects' and Builders' Pocket-book.
Rewritten Edition. 16mo, mor., 5 00
Merrill's Stones for Building and Decoration. 8vo, 5 00
Non-metallic Minerals: Their Occurrence and Uses. 8vo, 4 00
Monckton's Stair-building. 4to, 4 00
Patton's Practical Treatise on Foundations. 8vo, 5 00
Peabody's Naval Architecture. 8vo, 7 50
Rice's Concrete-block Manufacture. 8vo, 2 00
Richey's Handbook for Superintendents of Construction. 16mo, mor., 4 00
* Building Mechanics' Ready Reference Book:
* Carpenters' and Woodworkers' Edition. 16mo, morocco, 1 50
* Cementworkers and Plasterer's Edition. (In Press.)
* Stone- and Brick-mason's Edition. 12mo, mor., 1 50
Sabin's Industrial and Artistic Technology of Paints
and Varnish. 8vo, 3 00
Siebert and Biggin's Modern Stone-cutting and Masonry. 8vo, 1 50
Snow's Principal Species of Wood. 8vo, 3 50
Sondericker's Graphic Statics with Applications to Trusses,
Beams, and Arches. 8vo, 2 00
Towne's Locks and Builders' Hardware. 18mo, morocco, 3 00
Turneaure and Maurer's Principles of Reinforced Concrete
Construction. 8vo, 3 00
Wait's Engineering and Architectural Jurisprudence. 8vo, 6 00
Sheep, 6 50
Law of Operations Preliminary to Construction in
Engineering and Architecture. 8vo, 5 00
Sheep, 5 50
Law of Contracts. 8vo, 3 00
Wilson's Air Conditioning, (In Press.)
Wood's Rustless Coatings: Corrosion and Electrolysis of Iron
and Steel. 8vo, 4 00
Worcester and Atkinson's Small Hospitals, Establishment and
Maintenance, Suggestions for Hospital Architecture,
with Plans for a Small Hospital. 12mo, 1 25
The World's Columbian Exposition of 1893. Large 4to, 1 00
ARMY AND NAVY.
Bernadou's Smokeless Powder, Nitro-cellulose, and the Theory
of the Cellulose Molecule. 12mo, 2 50
Chase's Screw Propellers and Marine Propulsion. 8vo, 3 00
Cloke's Gunner's Examiner. 8vo, 1 50
Craig's Azimuth. 4to, 3 50
Crehore and Squier's Polarizing Photo-chronograph. 8vo, 3 00
* Davis's Elements of Law. 8vo, 2 50
* Treatise on the Military Law of United States. 8vo, 7 00
Sheep, 7 50
De Brack's Cavalry Outposts Duties. (Carr.) 24mo, morocco, 2 00
Dietz's Soldier's First Aid Handbook. 16mo, morocco, 1 25
* Dudley's Military Law and the Procedure of
Courts-martial. Large 12mo, 2 50
Durand's Resistance and Propulsion of Ships. 8vo, 5 00
* Dyer's Handbook of Light Artillery. 12mo, 3 00
Eissler's Modern High Explosives. 8vo, 4 00
* Fiebeger's Text-book on Field Fortification. Small 8vo, 2 00
Hamilton's The Gunner's Catechism. 18mo, 1 00
* Hoff's Elementary Naval Tactics. 8vo, 1 50
Ingalls's Handbook of Problems in Direct Fire. 8vo, 4 00
* Lissak's Ordnance and Gunnery. 8vo, 6 00
* Lyons's Treatise on Electromagnetic Phenomena.
Vols. I. and II. 8vo, each, 6 00
* Mahan's Permanent Fortifications. (Mercur.) 8vo, half morocco, 7 50
Manual for Courts-martial. 16mo, morocco, 1 50
* Mercur's Attack of Fortified Places. 12mo, 2 00
* Elements of the Art of War. 8vo, 4 00
Metcalfe's Cost of Manufactures--And the Administration
of Workshops. 8vo, 5 00
* Ordnance and Gunnery. 2 vols. 12mo, 5 00
Murray's Infantry Drill Regulations. 18mo, paper, 10
Nixon's Adjutants' Manual. 24mo, 1 00
Peabody's Naval Architecture. 8vo, 7 50
* Phelps's Practical Marine Surveying. 8vo, 2 50
Powell's Army Officer's Examiner. 12mo, 4 00
Sharpe's Art of Subsisting Armies in War. 18mo, morocco, 1 50
* Tupes and Poole's Manual of Bayonet Exercises and
Musketry Fencing. 24mo, leather, 50
Weaver's Military Explosives. 8vo, 3 00
Wheeler's Siege Operations and Military Mining. 8vo, 2 00
Winthrop's Abridgment of Military Law. 12mo, 2 50
Woodhull's Notes on Military Hygiene. 16mo, 1 50
Young's Simple Elements of Navigation. 16mo, morocco, 2 00
ASSAYING.
Fletcher's Practical Instructions in Quantitative
Assaying with the Blowpipe. 12mo, morocco, 1 50
Furman's Manual of Practical Assaying. 8vo, 3 00
Lodge's Notes on Assaying and Metallurgical Laboratory
Experiments. 8vo, 3 00
Low's Technical Methods of Ore Analysis. 8vo, 3 00
Miller's Manual of Assaying. 12mo, 1 00
Cyanide Process. 12mo, 1 00
Minet's Production of Aluminum and its Industrial Use.
(Waldo.) 12mo, 2 50
O'Driscoll's Notes on the Treatment of Gold Ores. 8vo, 2 00
Ricketts and Miller's Notes on Assaying. 8vo, 3 00
Robine and Lenglen's Cyanide Industry. (Le Clerc.) 8vo, 4 00
Ulke's Modern Electrolytic Copper Refining. 8vo, 3 00
Wilson's Cyanide Processes. 12mo, 1 50
Chlorination Process. 12mo, 1 50
ASTRONOMY.
Comstock's Field Astronomy for Engineers. 8vo, 2 50
Craig's Azimuth. 4to, 3 50
Crandall's Text-book on Geodesy and Least Squares. 8vo, 3 00
Doolittle's Treatise on Practical Astronomy. 8vo, 4 00
Gore's Elements of Geodesy. 8vo, 2 50
Hayford's Text-book of Geodetic Astronomy. 8vo, 3 00
Merriman's Elements of Precise Surveying and Geodesy. 8vo, 2 50
* Michie and Harlow's Practical Astronomy. 8vo, 3 00
* White's Elements of Theoretical and Descriptive Astronomy. 12mo, 2 00
BOTANY.
Davenport's Statistical Methods, with Special
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Thomé and Bennett's Structural and Physiological Botany. 16mo, 2 25
Westermaier's Compendium of General Botany. (Schneider.) 8vo, 2 00
CHEMISTRY.
* Abegg's Theory of Electrolytic Dissociation. (Von Ende.) 12mo, 1 25
Adriance's Laboratory Calculations and Specific Gravity
Tables. 12mo, 1 25
Alexeyeff's General Principles of Organic Synthesis.
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Allen's Tables for Iron Analysis. 8vo, 3 00
Arnold's Compendium of Chemistry. (Mandel.) Small 8vo, 3 50
Austen's Notes for Chemical Students. 12mo, 1 50
Beard's Mine Gases and Explosions. (In Press.)
Bernadou's Smokeless Powder.--Nitro-cellulose, and Theory
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Bolduan's Immune Sera. 12mo, 1 50
* Browning's Introduction to the Rarer Elements. 8vo, 1 50
Brush and Penfield's Manual of Determinative Mineralogy. 8vo, 4 00
* Claassen's Beet-sugar Manufacture. (Hall and Rolfe.) 8vo, 3 00
Classen's Quantitative Chemical Analysis by Electrolysis.
(Boltwood.) 8vo, 3 00
Cohn's Indicators and Test-papers. 12mo, 2 00
Tests and Reagents. 8vo, 3 00
Crafts's Short Course in Qualitative Chemical Analysis.
(Schaeffer.) 12mo, 1 50
* Danneel's Electrochemistry. (Merriam.) 12mo, 1 25
Dolezalek's Theory of the Lead Accumulator (Storage Battery).
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Drechsel's Chemical Reactions. (Merrill.) 12mo, 1 25
Duhem's Thermodynamics and Chemistry. (Burgess.) 8vo, 4 00
Eissler's Modern High Explosives. 8vo, 4 00
Effront's Enzymes and their Applications. (Prescott.) 8vo, 3 00
Erdmann's Introduction to Chemical Preparations. (Dunlap.) 12mo, 1 25
* Fischer's Physiology of Alimentation. Large 12mo, 2 00
Fletcher's Practical Instructions in Quantitative
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Fowler's Sewage Works Analyses. 12mo, 2 00
Fresenius's Manual of Qualitative Chemical Analysis. (Wells.) 8vo, 5 00
Manual of Qualitative Chemical Analysis. Part I.
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Quantitative Chemical Analysis. (Cohn.) 2 vols. 8vo, 12 50
Fuertes's Water and Public Health. 12mo, 1 50
Furman's Manual of Practical Assaying. 8vo, 3 00
* Getman's Exercises in Physical Chemistry. 12mo, 2 00
Gill's Gas and Fuel Analysis for Engineers. 12mo, 1 25
* Gooch and Browning's Outlines of Qualitative Chemical
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Grotenfelt's Principles of Modern Dairy Practice. (Woll.) 12mo, 2 00
Groth's Introduction to Chemical Crystallography. (Marshall.) 12mo, 1 25
Hammarsten's Text-book of Physiological Chemistry. (Mandel.) 8vo, 4 00
Hanausek's Microscopy of Technical Products. (Winton.) 8vo, 5 00
* Haskin's and MacLeod's Organic Chemistry. 12mo, 2 00
Helm's Principles of Mathematical Chemistry. (Morgan.) 12mo, 1 50
Hering's Ready Reference Tables (Conversion Factors.)
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Herrick's Denatured or Industrial Alcohol. 8vo, 4 00
Hind's Inorganic Chemistry. 8vo, 3 00
* Laboratory Manual for Students. 12mo, 1 00
Holleman's Text-book of Inorganic Chemistry. (Cooper.) 8vo, 2 50
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* Laboratory Manual of Organic Chemistry. (Walker.) 12mo, 1 00
Holley and Ladd's Analysis of Mixed Paints, Color Pigments,
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Hopkins's Oil-chemists' Handbook. 8vo, 3 00
Iddings's Rock Minerals. 8vo, 5 00
Jackson's Directions for Laboratory Work in Physiological
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Johannsen's Key for the Determination of Rock-forming Minerals
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Keep's Cast Iron. 8vo, 2 50
Ladd's Manual of Quantitative Chemical Analysis. 12mo, 1 00
Landauer's Spectrum Analysis. (Tingle.) 8vo, 3 00
* Langworthy and Austen. The Occurrence of Aluminium in
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Lassar-Cohn's Application of Some General Reactions to
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Leach's The Inspection and Analysis of Food with Special
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Löb's Electrochemistry of Organic Compounds. (Lorenz.) 8vo, 3 00
Lodge's Notes on Assaying and Metallurgical Laboratory
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Low's Technical Method of Ore Analysis. 8vo, 3 00
Lunge's Techno-chemical Analysis. (Cohn.) 12mo 1 00
* McKay and Larsen's Principles and Practice of Butter-making. 8vo, 1 50
Maire's Modern Pigments and their Vehicles. (In Press.)
Mandel's Handbook for Bio-chemical Laboratory. 12mo, 1 50
* Martin's Laboratory Guide to Qualitative Analysis with
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Mason's Water-supply. (Considered Principally from a Sanitary
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Examination of Water. (Chemical and Bacteriological.) 12mo, 1 25
Matthews's The Textile Fibres. 2d Edition, Rewritten. 8vo, 4 00
Meyer's Determination of Radicles in Carbon Compounds.
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Miller's Manual of Assaying. 12mo, 1 00
Cyanide Process. 12mo, 1 00
Minet's Production of Aluminum and its Industrial Use.
(Waldo.) 12mo, 2 50
Mixter's Elementary Text-book of Chemistry. 12mo, 1 50
Morgan's An Outline of the Theory of Solutions and its
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Elements of Physical Chemistry. 12mo, 3 00
* Physical Chemistry for Electrical Engineers. 12mo, 5 00
Morse's Calculations used in Cane-sugar Factories. 16mo, morocco, 1 50
* Muir's History of Chemical Theories and Laws. 8vo, 4 00
Mulliken's General Method for the Identification of Pure
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O'Driscoll's Notes on the Treatment of Gold Ores. 8vo, 2 00
Ostwald's Conversations on Chemistry. Part One. (Ramsey.) 12mo, 1 50
" " " " Part Two. (Turnbull.) 12mo, 2 00
* Palmer's Practical Test Book of Chemistry. 12mo, 1 00
* Pauli's Physical Chemistry in the Service of Medicine.
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* Penfield's Notes on Determinative Mineralogy and
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Pictet's The Alkaloids and their Chemical Constitution.
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Pinner's Introduction to Organic Chemistry. (Austen.) 12mo, 1 50
Poole's Calorific Power of Fuels. 8vo, 3 00
Prescott and Winslow's Elements of Water Bacteriology, with
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* Reisig's Guide to Piece-dyeing. 8vo, 25 00
Richards and Woodman's Air, Water, and Food from a Sanitary
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Ricketts and Miller's Notes on Assaying. 8vo, 3 00
Rideal's Sewage and the Bacterial Purification of Sewage. 8vo, 4 00
Disinfection and the Preservation of Food. 8vo, 4 00
Riggs's Elementary Manual for the Chemical Laboratory. 8vo, 1 25
Robine and Lenglen's Cyanide Industry. (Le Clerc.) 8vo, 4 00
Ruddiman's Incompatibilities in Prescriptions. 8vo, 2 00
* Whys in Pharmacy. 12mo, 1 00
Sabin's Industrial and Artistic Technology of Paints and
Varnish. 8vo, 3 00
Salkowski's Physiological and Pathological Chemistry.
(Orndorff.) 8vo, 2 50
Schimpf's Text-book of Volumetric Analysis. 12mo, 2 50
Essentials of Volumetric Analysis. 12mo, 1 25
* Qualitative Chemical Analysis. 8vo, 1 25
Smith's Lecture Notes on Chemistry for Dental Students. 8vo, 2 50
Spencer's Handbook for Chemists of Beet-sugar Houses.
16mo, morocco, 3 00
Handbook for Cane Sugar Manufacturers. 16mo, morocco, 3 00
Stockbridge's Rocks and Soils. 8vo, 2 50
* Tillman's Elementary Lessons in Heat. 8vo, 1 50
* Descriptive General Chemistry. 8vo, 3 00
Treadwell's Qualitative Analysis. (Hall.) 8vo, 3 00
Quantitative Analysis. (Hall.) 8vo, 4 00
Turneaure and Russell's Public Water-supplies. 8vo, 5 00
Van Deventer's Physical Chemistry for Beginners. (Boltwood.) 12mo, 1 50
* Walke's Lectures on Explosives. 8vo, 4 00
Ware's Beet-sugar Manufacture and Refining. Vol. I. Small 8vo, 4 00
" " " " " Vol. II. Small 8vo, 5 00
Washington's Manual of the Chemical Analysis of Rocks. 8vo, 2 00
Weaver's Military Explosives. 8vo, 3 00
Wehrenfennig's Analysis and Softening of Boiler Feed-Water. 8vo, 4 00
Wells's Laboratory Guide in Qualitative Chemical Analysis. 8vo, 1 50
Short Course in Inorganic Qualitative Chemical Analysis
for Engineering Students. 12mo, 1 50
Text-book of Chemical Arithmetic. 12mo, 1 25
Whipple's Microscopy of Drinking-water. 8vo, 3 50
Wilson's Cyanide Processes. 12mo, 1 50
Chlorination Process. 12mo, 1 50
Winton's Microscopy of Vegetable Foods. 8vo, 7 50
Wulling's Elementary Course in Inorganic, Pharmaceutical,
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CIVIL ENGINEERING.
BRIDGES AND ROOFS. HYDRAULICS. MATERIALS OF ENGINEERING. RAILWAY
ENGINEERING.
Baker's Engineers' Surveying Instruments. 12mo, 3 00
Bixby's Graphical Computing Table. Paper 19-1/2 × 24-1/4 inches, 25
Breed and Hosmer's Principles and Practice of Surveying. 8vo, 3 00
* Burr's Ancient and Modern Engineering and the Isthmian Canal.
8vo, 3 50
Comstock's Field Astronomy for Engineers. 8vo, 2 50
* Corthell's Allowable Pressures on Deep Foundations. 12mo, 1 25
Crandall's Text-book on Geodesy and Least Squares. 8vo, 3 00
Davis's Elevation and Stadia Tables. 8vo, 1 00
Elliott's Engineering for Land Drainage. 12mo, 1 50
Practical Farm Drainage. 12mo, 1 00
* Fiebeger's Treatise on Civil Engineering. 8vo, 5 00
Flemer's Phototopographic Methods and Instruments. 8vo, 5 00
Folwell's Sewerage. (Designing and Maintenance.) 8vo, 3 00
Freitag's Architectural Engineering. 2d Edition, Rewritten. 8vo, 3 50
French and Ives's Stereotomy. 8vo, 2 50
Goodhue's Municipal Improvements. 12mo, 1 50
Gore's Elements of Geodesy. 8vo, 2 50
* Hauch and Rice's Tables of Quantities for Preliminary
Estimates. 12mo, 1 25
Hayford's Text-book of Geodetic Astronomy. 8vo, 3 00
Hering's Ready Reference Tables (Conversion Factors).
16mo, morocco, 2 50
Howe's Retaining Walls for Earth. 12mo, 1 25
Hoyt and Grover's River Discharge. 8vo, 2 00
* Ives's Adjustments of the Engineer's Transit and Level.
16mo, Bds. 25
Ives and Hilts's Problems in Surveying. 16mo, morocco, 1 50
Johnson's (J. B.) Theory and Practice of Surveying. Small 8vo, 4 00
Johnson's (L. J.) Statics by Algebraic and Graphic Methods. 8vo, 2 00
Laplace's Philosophical Essay on Probabilities.
(Truscott and Emory.) 12mo, 2 00
Mahan's Treatise on Civil Engineering. (1873.) (Wood.) 8vo, 5 00
* Descriptive Geometry. 8vo, 1 50
Merriman's Elements of Precise Surveying and Geodesy. 8vo, 2 50
Merriman and Brooks's Handbook for Surveyors. 16mo, morocco, 2 00
Nugent's Plane Surveying. 8vo, 3 50
Ogden's Sewer Design. 12mo, 2 00
Parsons's Disposal of Municipal Refuse. 8vo, 2 00
Patton's Treatise on Civil Engineering. 8vo half leather, 7 50
Reed's Topographical Drawing and Sketching. 4to, 5 00
Rideal's Sewage and the Bacterial Purification of Sewage. 8vo, 4 00
Riemer's Shaft-sinking under Difficult Conditions.
(Corning and Peele.) 8vo, 3 00
Siebert and Biggin's Modern Stone-cutting and Masonry. 8vo, 1 50
Smith's Manual of Topographical Drawing. (McMillan.) 8vo, 2 50
Sondericker's Graphic Statics, with Applications to
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Taylor and Thompson's Treatise on Concrete, Plain and
Reinforced. 8vo, 5 00
Tracy's Plane Surveying. 16mo, morocco, 3 00
* Trautwine's Civil Engineer's Pocket-book. 16mo, morocco, 5 00
Venable's Garbage Crematories in America. 8vo, 2 00
Wait's Engineering and Architectural Jurisprudence. 8vo, 6 00
Sheep, 6 50
Law of Operations Preliminary to Construction in
Engineering and Architecture. 8vo, 5 00
Sheep, 5 50
Law of Contracts. 8vo, 3 00
Warren's Stereotomy--Problems in Stone-cutting. 8vo, 2 50
Webb's Problems in the Use and Adjustment of
Engineering Instruments. 16mo, morocco, 1 25
Wilson's Topographic Surveying. 8vo, 3 50
BRIDGES AND ROOFS.
Boller's Practical Treatise on the Construction of Iron
Highway Bridges. 8vo, 2 00
Burr and Falk's Influence Lines for Bridge and Roof
Computations. 8vo, 3 00
Design and Construction of Metallic Bridges. 8vo, 5 00
Du Bois's Mechanics of Engineering. Vol. II. Small 4to, 10 00
Foster's Treatise on Wooden Trestle Bridges. 4to, 5 00
Fowler's Ordinary Foundations. 8vo, 3 50
Greene's Roof Trusses. 8vo, 1 25
Bridge Trusses. 8vo, 2 50
Arches in Wood, Iron, and Stone. 8vo, 2 50
Grimm's Secondary Stresses in Bridge Trusses. (In Press.)
Howe's Treatise on Arches. 8vo, 4 00
Design of Simple Roof-trusses in Wood and Steel. 8vo, 2 00
Symmetrical Masonry Arches. 8vo, 2 50
Johnson, Bryan, and Turneaure's Theory and Practice in
the Designing of Modern Framed Structures. Small 4to, 10 00
Merriman and Jacoby's Text-book on Roofs and Bridges:
Part I. Stresses in Simple Trusses. 8vo, 2 50