THE TRIUMPH OF THE AEROPLANE
Balloon versus aeroplane, p. 272--The kite as a flying machine,
p. 273--How the air sustains a heavier-than-air mechanism, p.
274--Langley's early experiments, p. 275--Experiments in soaring,
p. 277--Lilienthal's imitation of the soaring bird, p. 279--Sir
Hiram Maxim's flying machine, p. 283--Langley's successful
aerodrome, p. 284--The failure of Langley's larger aerodrome,
p. 287--Wilbur and Orville Wright accomplish the impossible, p.
288--The first public demonstration by the Wright brothers, p.
290--The Wright aeroplane described, p. 291--A host of imitators,
p. 292--Mr. Henry Farman's successful flights, p. 293--Public
demonstrations by the Wright brothers in America and France, p.
293--The English Channel crossed by Blériot, p. 294--Orville
Wright fulfils the Government tests, p. 295--Spectacular
cross-country flights, p. 296--The Wright brothers the true
pioneers, p. 300.
ILLUSTRATIONS
THE WRIGHT AEROPLANE IN FRANCE IN 1908 _Frontispiece_
_Facing page_
"TAKING THE SUN" WITH THE SEXTANT 22
THE OLD AND THE NEW--A CONTRAST 60
MARINE ENGINES AND AN EARLY TYPE OF STEAMBOAT 64
THE STEAMSHIPS "CHARLOTTE DUNDAS" AND "CLERMONT" 68
THE "CLERMONT" 72
ROBERT FULTON 98
THE AMERICAN SUBMARINE BOAT "CUTTLEFISH" IN DRY DOCK AT
THE BROOKLYN NAVY YARD 108
A FLEET OF BRITISH SUBMARINES MANŒUVERING AT THE SURFACE 116
GEORGE STEPHENSON 124
A CENTURY'S PROGRESS IN LOCOMOTIVE BUILDING 128
CUGNOT'S TRACTION ENGINE AND THE "NOVELTY" LOCOMOTIVE 132
THE FAMOUS LOCOMOTIVES "ROCKET" AND "SANS-PAREIL" 134
THE DEVELOPMENT OF THE LOCOMOTIVE 150
THE HOBBY-HORSE OF 1820 CONTRASTED WITH THE MOTOR CYCLE
OF TO-DAY 154
THE EVOLUTION OF THE BICYCLE 156
THE EXTREMES OF AUTOMOBILE DEVELOPMENT 158
AN ENGLISH STEAM COACH OF 1827 AND A NEW YORK TAXICAB
OF 1909 162
A RACING AUTOMOBILE 166
RETROSPECT AND PROSPECT IN TRANSPORTATION--THE DE WITT
CLINTON TRAIN AND THE GYROCAR 200
TWO VIEWS OF MR. LOUIS BRENNAN'S MONORAIL GYROCAR 216
AN INTERNATIONAL BALLOON RACE 242
TWO FAMOUS FRENCH WAR BALLOONS 264
THE ZEPPELIN DIRIGIBLE BALLOON 266
AN ENGLISH DIRIGIBLE BALLOON 268
ENGLISH AND AMERICAN DIRIGIBLE WAR BALLOONS AND A
WRIGHT AEROPLANE 270
THE AEROPLANE OF M. SANTOS-DUMONT 272
LEARNING HOW TO FLY 278
FLYING MACHINES OF THE MONOPLANE TYPE 284
THE WRIGHT AEROPLANE 288
MR. WILBUR WRIGHT PREPARING TO ASCEND IN HIS AEROPLANE
WITH HIS PUPIL M. CASSANDIER 292
THE FARMAN AEROPLANE 294
THE MONOPLANES OF BLÉRIOT AND LATHAM 296
A BRITISH AEROPLANE 298
MR. WILBUR WRIGHT FLYING OVER NEW YORK HARBOR,
OCTOBER 4, 1909 300
THE CONQUEST OF TIME AND SPACE
INTRODUCTION
The preceding volume dealt with the general principles of application
and transformation of the powers of Nature through which the world's
work is carried on. In the present volume we are chiefly concerned
with man's application of the same principles in his efforts to set at
defiance, so far as may be, the limitations of time and space.
Something has already been said as to the contrast between the
material civilization of to-day and that of the generations prior to
the nineteenth century. The transformation in methods of agriculture
and manufacture has been referred to somewhat in detail. Now we
have to do with contrasts that are perhaps even more vivid, since
they concern conditions that come within the daily observation of
everyone. Steamships, locomotives, electric cars, and automobiles,
are such commonplaces of every-day life that it is difficult to
conceive a world in which they have no part. Yet everyone is aware
that all these mechanisms are inventions of the nineteenth century.
Meantime the aeroplane, which bids fair to rival those other means
of transportation in the near future, is a creation of the twentieth
century.
In order to visualize the contrast between the practical civilization
of to-day and that of our grandparents, it suffices to recall that the
first steam locomotive that carried passengers over a railway was put
in operation in the year 1829; and that the first ship propelled by
steam power alone did not cross the ocean until 1838. Not until well
towards the middle of the nineteenth century, then, were the conditions
of transportation altered materially from what they had been since the
very dawn of civilization,--conditions under which one hundred miles
constituted about the maximum extent of a hard day's land journey.
The elaboration of railway and steamship lines through which nearly
all portions of the habitable globe have been made accessible, has
constituted one of the most remarkable examples of economic development
that man has ever achieved. It requires but the slightest use of the
imagination to realize with some measure of vividness the extent to
which the entire structure of present-day civilization is based upon
this elaboration of means of transportation. To point but a single
illustration, the entire central and western portion of the United
States must have remained a wilderness for decades or centuries had not
the steam locomotive made communication easy between these regions and
the seaboard.
Contrariwise no such development of city life as that which we see
throughout Christendom would have been possible but for the increased
facilities, due primarily to locomotives and steamships, for bringing
all essential food-stuffs from distant regions.
What this all means when applied on a larger scale may be suggested
by the reflection that the entire character of the occupation of the
average resident of England has been changed within a century. A
century ago England was a self-supporting nation, in the sense that
it produced its own food-stuffs. To-day the population of England as
a whole is dependent upon food shipped to it from across the oceans.
Obviously such a transformation could never have been effected had
not the application of steam revolutionized the entire character of
transportation.
Far-reaching as are the economic aspects of the problem of
transportation, this extraordinary revolution, the effects of which
are visible on every side, has been brought about by the application
of only a few types of mechanisms. The steam engine, the dynamo, and
the gas engine are substantially responsible for the entire development
in question. In the succeeding pages, which deal with the development
of steamships, locomotives, automobiles, and flying machines, we have
to do with the application of principles with which our previous
studies have made us familiar; and in particular with the mechanisms
that have engaged our attention in the preceding volume. Yet the
application of these principles and the utilization of these mechanisms
gave full opportunity for the exercise of inventive ingenuity, and
the story of the development of steamships, locomotives, electric
vehicles, automobiles, gyro cars, and flying machines, will be found
to have elements of interest commensurate with the importance of these
mechanisms themselves. Before we take up these stories in detail,
however, we shall briefly review the story of geographical discovery
and exploration in its scientific aspects.
I
THE CONQUEST OF THE ZONES
The contrast between modern and ancient times is strikingly suggested
by reflection on the limited range of geographical knowledge of those
Oriental and Classical nations who dominated the scene at that remote
period which we are accustomed to characterize as the dawn of history.
The Egyptians, peopling the narrow valley of the Nile, scarcely had
direct dealings with any people more remote than the Babylonians
and Assyrians occupying the valley of the Euphrates. Babylonians
and Assyrians in turn were in touch with no Eastern civilization
more remote than that of Persia and India, and knew nothing of any
Western world beyond the borders of Greece. Greeks and Romans, when
in succession they came to dominate the world stage,--developing a
civilization which even as viewed from our modern vantage-ground seems
marvelous,--were still confined to narrow strips of territory about the
shores of the Mediterranean, and had but the vaguest notions as to any
other regions of the earth.
In the later classical period, to be sure, the globe was subjected,
as we have seen, to wonderful measurements by Eratosthenes and by
Posidonius, and the fact that man's abiding place is a great ball
utterly different from the world as conceived by the Oriental mind,
was definitely grasped and became more or less a matter of common
knowledge. It was even conceived that there might be a second habitable
zone on the opposite side of the equator from the region in which
the Greeks and Romans found themselves, but as to just what this
hypothetical region might be like, and as to what manner of beings
might people it, even the most daring speculator made no attempt
to decide. The more general view, indeed, precluded all thought of
habitable regions lying beyond the confines of the Mediterranean
civilization; conceiving rather that the world beyond was a mere waste
of waters.
Doubtless the imaginative mind of the period must have chafed under
these restrictions of geographical knowledge; and now and again a more
daring navigator must have pressed out beyond the limits of safety,
into the Unknown, never to return. Once at least, even in the old
Egyptian days, a band of navigators surpassing in daring all their
predecessors, and their successors of the ensuing centuries, made bold
to continue their explorations along the coast of Africa till they had
passed to a region where--as Herodotus relates with wonder--the sun
appeared "on their right hand," ultimately passing about the southern
extremity of the African continent and in due course completing the
circumnavigation, returning with wonder tales to excite the envy,
perhaps, but not the emulation of their fellows.
Then in due course some Phœnician or Greek navigators coasted along the
northern shores beyond the "Pillars of Hercules" and discovered at the
very confines of the world what we now term the British Isles. But this
was the full extent of exploration throughout antiquity; and the spread
of civilization about the borders of the known world was a slow and
haphazard procedure during all those centuries that mark the Classical
and Byzantine periods.
THE MARINER'S COMPASS
The change came with that revival of scientific learning which was
to usher in the new era that we speak of as modern times. And here
as always it was a practical mechanism that gave the stimulus to new
endeavor. In this particular case the implement in question was the
mariner's compass, which consists, in its essentials, as everyone is
aware, of a magnetized needle floated or suspended in such a way that
it is made under the influence of terrestrial magnetism to point to the
north and south.
The mysterious property whereby the magnetized needle obeys this
inscrutable impulse is, in the last analysis, inexplicable even to
the science of our day. But the facts, in their cruder relations,
had been familiar from time immemorial to a nation whose habitat lay
beyond the ken of the classical world--namely, the Chinese. It seems
to be fairly established that navigators of that nation had used the
magnetized needle, so arranged as to constitute a crude compass, from
a period possibly antedating the Christian Era. To Western nations,
however, the properties of the magnetized needle seem to have
been quite unknown--at least its possibilities of practical aid to
the navigator were utterly unsuspected--until well into the Middle
Ages. There is every reason to believe--though absolute proof is
lacking--that a knowledge of the compass came to the Western world from
the Far East through the medium of the Arabs. The exact channel of
this communication will perhaps always remain unknown. Nor have we any
clear knowledge as to the exact time when the all-important information
was transmitted. We only know that manuscripts of the twelfth century
mentioned the magnetic needle as an implement familiar to navigators,
and from this time forward, we may feel sure, the new possibilities of
exploration made possible by the compass must have suggested themselves
to some at least of the more imaginative minds of each generation.
Indeed there were explorers in each generation who pushed out a little
into the unknown, as the discovery of various groups of Islands in
the Atlantic shows, although the efforts of these pioneers have been
eclipsed by the spectacular feat of Columbus.
The exact steps by which the crude compass of the Orientals was
developed into the more elaborate and delicate instrument familiar to
Western navigators cannot be traced by the modern historian. It is
known that sundry experiments were made as to the best form of needle,
and in particular as to the best way of adjusting it on approximately
frictionless bearings. But a high degree of perfection in this regard
had been attained before the modern period; and the compass had
been further perfected by attaching the needle to a circumferential
card on which the "points of the compass," thirty-two in number,
were permanently marked. At all events the compass card had been so
divided before the close of the fourteenth century, as is proved by
a chance reference by Chaucer. The utility of the instrument thus
perfected--indeed its entire indispensableness--was doubtless by this
time clearly recognized by all navigators; and one risks nothing in
suggesting that without the compass no such hazardous voyage into the
unknown as that of Columbus would ever have been attempted.
No doubt the earliest observers of the needle believed that it pointed
directly to the North. If such were indeed the fact the entire science
of navigation would be vastly simpler than it is. But it required no
very acute powers of observation to discover that the magnetized needle
does not in reality point directly towards the earth's poles. There
are indeed places on the earth where it does so point, but in general
it is observed to deviate by a few degrees from the exact line of the
meridian. Such deviation is technically known as magnetic declination.
That this declination is not the same for all places was discovered by
Columbus in the course of his first transatlantic voyage.
A century or so later, the accumulated records made it clear that
declination is not a fixed quantity even at any given place. An
Englishman, Stephen Burrows, is credited with making the discovery
that the needle thus shifts its direction slightly with the lapse
of time, and the matter was more clearly determined a little later
by Gillebrand, Professor of Geometry at Graham College. Dr. Halley,
the celebrated astronomer--whose achievements have been recalled to
succeeding generations by the periodical return of the comet that bears
his name--gave the matter attention, and in a paper before the Royal
Society in 1692 he pointed out that the direction of the needle at
London had changed in a little over a century (between 1580 and 1692)
from 11 degrees 15 minutes East to 6 degrees West, or more than 17
degrees.
Halley conclusively showed that similar variations occurred at all
other places where records had been kept. He had already demonstrated,
a few years earlier, that the deviations of the compass noted at sea
are not due to the varying attractions of neighboring bodies of land,
but to some influence having to do with the problem of terrestrial
magnetism in its larger aspects. Halley advocated the doctrine, which
had first been put forward by William Gilbert, that the earth itself
is a gigantic magnet, and that the action of the compass is dependent
upon this terrestrial source and not, as many navigators believed, on
the influence of a magnetic star, or on localized deposits of lodestone
somewhere in the unknown regions of the North.
Further observations of the records presently made it clear that there
are also annual and even daily variations of the compass of slight
degree. The fact of diurnal variations was first discovered by Mr.
Graham about the year 1719. More than half a century later it was
observed by an astronomer named Wales, who was accompanying Captain
Cook on his famous voyage round the world (1772-74), that there is yet
another fluctuation of the compass due to the influence of the ship
on which it is placed. Considerable quantities of iron were of course
used in the construction of wooden ships, and it was made clear that
the ship itself comes under the influence of the earth's magnetism and
exerts in turn an appreciable influence on the compass. The fluctuation
due to this source is known as deviation, in contradistinction to the
larger fluctuation already referred to as declination.
Not only is the deviation due to the ship's influence a matter of
importance, but it was discovered by Captain Matthew Flinders, in the
course of his explorations along the coast of New Holland in the year
1801-02, that the influence of the ship over its compass varies with
the direction of the ship's prow.
Needless to say, the problem of the deviation of the compass due to the
influence of the ship is enormously complicated when the ship instead
of being constructed chiefly of wood is made of iron or steel. It then
becomes absolutely essential that the influence of vessels shall be
reckoned with and so far as possible compensated. Such compensation may
be effected by the adjustment of bodies of iron, as first suggested
by Barlow, or by the use of permanent magnets, as first attempted
by England's Astronomer Royal, Professor Airy. At the very best,
however, it is never possible totally to overcome the ship's perverting
influence, allowance for which must be made if an absolutely accurate
conclusion is to be drawn from the record presented by the compass.
Early in the twentieth century an American ship, christened the
_Carnegie_, in honor of the philanthropist who supplied funds for the
enterprise, was constructed for the express purpose of making accurate
charts of the lines of magnetic declination in various parts of the
globe. This ship differs from every other vessel of considerable size
ever hitherto constructed in that no magnetic material of any kind
was used in connection with its structure or equipment. For the most
part iron was substituted by copper or other non-magnetic metal.
Pins of locust-wood largely took the place of nails; and wherever it
was not feasible to do away with iron altogether it was used in the
form of non-magnetic manganese steel. The purpose of the _Carnegie_
is to provide accurate charts of magnetic declination for the use
of navigators in general. The value of observations made with this
non-magnetic ship will be clear when it is reflected that with an
ordinary ship the observer can never be absolutely certain as to what
precise share of the observed fluctuation of the compass is due at any
given moment to the ship's influence. In other words--using technical
terminology--he can never apportion with absolute accuracy the
influence of declination and of deviation. Yet it is highly important
that he should be able to do so, inasmuch as the declination of the
compass is an all-important element in reckoning the exact location of
the ship, and would be the same for every ship at that place, whereas
deviation denotes a purely local disturbance which would never be the
same for any two ships of different construction.
Not only does the magnetized needle thus tend to vary in the direction
of its horizontal action, but it also tends when suspended at the
middle to shift its vertical axis. In regions near the equator, indeed,
the magnetized needle maintains a horizontal position, but if carried
into northern or southern latitudes it progressively "dips," its
polar end sinking lower and lower. This dipping of the needle seems
to have been first observed by Robert Norman, an English nautical
instrument maker, about the year 1590. It was brought to the attention
of Gilbert and carefully tested by him in the course of his famous
pioneer experiments. Gilbert was led to predicate the existence of
magnetic poles, the exact location of which would be indicated by the
dipping needle, which, sinking lower and lower as northern latitudes
were attained, would ultimately at the magnetic pole itself assume a
vertical direction.
That this is a correct expression of the facts was determined in
the year 1831 by Sir James Ross, who in the course of his Arctic
explorations observed the vertical dip and so located the northern
magnetic pole at about 70 degrees 5 minutes north latitude and 96
degrees 43 minutes west longitude. It was thus proved that the magnetic
pole is situated a long distance--more than 1,200 miles--from the
geographical pole. The location of the south magnetic pole was most
accurately determined in 1909 by Lieutenant Shackleton's expedition at
about 73 degrees south latitude and 156 degrees east longitude. The two
magnetic poles are thus not directly opposite each other on the earth's
surface, and the magnetic axis of the earth does not coincide with the
geographical center of the globe itself.
From the standpoint of practical navigation the dip of the needle is
a matter of much less significance than its horizontal fluctuations.
Robert Norman himself attempted to overcome the dip by a balancing
apparatus applied to the needle; and the modern compass is suspended
in such a way that the propensity to dip does not interfere with
the lateral movements which supply the navigator with all important
information. The modern compass in question is the invention of
Lord Kelvin and was patented by him in 1876. It consists of a
number of small magnets arranged in parallel and held in position
by silk threads, each suspended, cobweb-like, from the circular
rim of aluminum. The weight--which in the aggregate is relatively
slight--being thus largely at the circumference, the instrument has a
maximum period of oscillation and hence a high degree of stability. Its
fluctuations due to the ship's influence are corrected by a carefully
adjusted disposition of metal balls and magnets.
SAILING BY DEAD RECKONING
While the compass gives indispensable information as to direction,
and is constantly under the eye of the pilot, it of course can give
no direct information as to the distance traversed by the ship, and
hence does not by itself suffice to tell the navigator his whereabouts.
In the early days there was indeed an expectation that the observed
declination of the compass would reveal to the navigator his longitude
and that the observation of the dip might enable him to determine his
latitude. But more extended observation shows that this was asking
altogether too much of the compass, and while it may be useful as
an accessory it is by no means the navigator's chief reliance in
determining his location. This is accomplished, as everyone is aware,
in clear weather by the observation of the heavenly bodies. In cloudy
weather, however, such observations obviously cannot be made, and the
seaman must direct his ship and estimate his location--an all important
matter when he is approaching the coast--by what is called dead
reckoning. One element of this reckoning is furnished by the compass,
inasmuch as that is his sole guide in determining the direction of
the ship's progress. The other element is supplied by the log which
furnishes him a clue as to the distance traversed hour by hour.
It is rather startling to reflect that the navigators of the middle
ages had no means whatever of determining the rate of progress of a
ship at sea, beyond the crudest guesses unaided by instrument of any
kind. When Columbus made his voyage he had no means of knowing what
distance he had actually sailed; nor was any method of measuring the
ship's speed utilized throughout the course of the ensuing century. In
the year 1570, however, one Humfray Cole suggested a theoretical means
of measuring the ship's rate of progress by means of an object dropped
back of the ship and allowed to drag through the water; and this
suggestion led a generation later to the introduction of the log, which
was first actually tested, so far as can be learned, in the year 1607.
The original log was so called because it consisted essentially of
an actual log or piece of wood. To the center of this a string was
attached, and in testing the ship's rate of progress this string was
allowed to slip through the fingers of a sailor who counted the number
of knots--placed, of course, at regular intervals on the string--that
passed through his fingers in a given time. As the log itself would
remain practically stationary in the water where it was dropped, the
number of knots counted indicated the distance traversed by the ship in
a given time. In practice the time was usually gauged by a half-minute
sand glass, and the knots were arranged at such a distance on the cord
that, in the course of the half minute, one knot would pass through
the fingers for each nautical mile covered by the ship in an hour. The
actual distance between the knots was therefore about fifty feet. The
nautical or geographical mile represents one degree of the earth's
circumference at the equator, amounting therefore to 6,008 feet, as
against the 5,280 feet of the statute mile. It was the use of the
log-line with its knots, as just explained, that led to the dubbing
of the nautical mile by the name "knot," which is still familiarly
employed, though the knotted log-line itself has been superseded in
recent times, except on very old-fashioned sailing ships.
The log retains its place even in the most modern ship, though its form
is materially altered, and its importance is somewhat lessened owing to
the fact that the experienced skipper can test the speed of his ship
very accurately by noting the number of revolutions per minute of the
ship's propellers. It is indeed the ship's propeller that supplies
the model for the modern log, in which the primitive piece of wood is
replaced by a torpedo-like piece of metal with miniature propeller-like
blades at its extremity. This apparatus is towed at the end of a long
line, and its blades, whirling more or less rapidly according to the
speed of the ship, communicate their motion to a recording apparatus,
adjusted at the ship's stern, to which the line is attached and the
face of which ordinarily presents a dial on which the speed of the ship
may be observed as readily as one observes the time by the clock.
Some recent modifications of the log employ an electrical device to
register the progress, but the principle of the revolving vanes, which
owe their speed to the rate at which they are dragged through the
water, is the fundamental one upon which the action of the log usually
depends, though attempts have been made to substitute pressure-gauge
systems.
While the modern log records the speed of the ship with a fair degree
of accuracy, its register shows at best only an approximation of the
facts. As already mentioned, the rate of revolution of the ship's
propeller blades furnishes what most navigators regard as a rather more
dependable test of speed. An apparatus for recording this is found on
the bridge of the modern ship. But due allowance must of course be made
for the effect of winds, waves, and ocean currents. These constantly
variable factors obviously make the estimate as to the precise distance
traversed by a ship in a given time a matter not altogether devoid of
guess work; and no navigator who has been obliged to sail for several
days by dead reckoning approaches a coast with quite the same degree
of satisfaction that he may entertain if his log has been checked by
observation of the sun or stars. In case, however, a navigator is able
to check his reckoning by astronomical observations, aided by the
chronometer, he determines his location with great accuracy.
THE DEVELOPMENT OF THE SEXTANT
The instrument with which such astronomical observations are made is
known as the sextant. Its purpose is to measure with great accuracy the
angle between two objects, which in practice are the horizon line on
one hand and some celestial body, usually the sun, on the other. The
determination of the latitude of the ship, for example, is a matter of
comparative ease, if the sun chances to be unobscured just at midday.
The navigator has merely to measure the exact elevation of the sun as
it crosses the meridian,--that is to say when it is at its highest
point,--and, having made certain corrections for so-called dip and
refraction, to which we shall refer more at length in a moment, a very
simple calculation reveals the latitude--that is to say, the distance
from the terrestrial equator.
That the latitude of a ship could thus be determined, with greater or
less accuracy, has been familiar knowledge to seamen from a very early
period. It was by the use of this principle that the earth was measured
by Eratosthenes and Posidonius in classical times, and the sailors of
antiquity probably carried with them a crude apparatus for measuring
the height of sun and stars, as the mediæval navigators are known to
have done.
The simplest and crudest form of measurer of which the record has been
preserved is known as the cross-staff. This consisted essentially of a
stick about a yard in length, called the staff, on which a cross-piece
was arranged at right angles, so adjusted at the center as to slide
back and forth on the staff. An eye-piece at one end of the staff was
utilized to sight along projections at either end of the cross-piece.
If the apparatus is held so that one of the lines of sight is directed
to the horizon, and then the cross-piece slid along the staff until
the other line of sight is directed toward the sun or a given star,
the angle between the two lines of sight will obviously represent the
angle of altitude of the celestial body in question. But the difficulty
of using an apparatus which requires two successive observations to be
made without shift of position is obvious, and it is clear that the
information derived from the cross-staff must have been at best very
vague--by no means such as would satisfy the modern navigator.
Even the navigators of the fifteenth century were aware of the
deficiencies of the cross-staff and sought to improve upon it. The
physicians of Henry the Navigator of Portugal, Roderick and Joseph by
name, and another of his advisers, Martin de Bohemia, are credited
with inventing, or at least introducing, a much improved apparatus
known as the astrolabe. This consists of a circle of metal, arranged
to be suspended from a ring at the side, so that one of its diameters
would maintain the horizontal position through the effect of gravity.
A superior quadrant of the circle was marked with degrees and minutes.
A straight piece of metal, with sights so that it could be accurately
pointed, was adjusted to revolve on a pivot at the center of the
circle. This sighting piece being aimed at the sun, for example, the
elevation of that body could be read directly on the measuring arc
of the circle. Here, then, was no new principle involved, but the
instrument had obvious points of advantage over the cross-staff, in
particular because only a single sight need be taken, the horizon
line being determined, as already explained, through the action of
gravitation.
The astrolabe did not gain immediate favor with practical navigators,
and it was at best a rather clumsy instrument, subject to peculiar
difficulties when used on a rolling ship. Many attempts were made to
improve upon it, but for a long time none of these was altogether
successful. The final suggestion as to means of overcoming the
difficulties encountered in measuring the altitude of astronomical
bodies was made by Sir Isaac Newton. But nothing practical came of
his discovery, as it was not published until a long time after his
death. Meantime independent discovery of the same principle was
made by Thomas Godfrey of Philadelphia, in 1730, and by the English
astronomer Hadley, who published his discovery before the Royal Society
in 1731. The instrument which Hadley devised was called a quadrant.
The principle on which it worked involved nothing more complex than
the use of two mirrors, one of them (known as the horizon glass and
having only half its surface mirrored) fixed in the line of vision of
a small telescope; the other (called the index mirror) movable with
the arm of an indicator, which is so adjusted as to revolve about the
axis of the quadrant. In operation these two mirrors enable the images
of two objects, the distance between which is to be measured, to be
superimposed. The telescope may be pointed at the horizon, for example,
directly under the position of the sun, and the arm of the instrument,
altering the position of the so-called index mirror, may be rotated
until the limb of the sun seems just to touch the horizon--the latter
being viewed through the unsilvered half of the horizon glass. The
scale at the circumference of the instrument is marked in half-degrees,
which, however, are registered as whole degrees, and which, so
interpreted, give the direct measurement of the angular distance
between the horizon and the sun; in other words the measurement of the
sun's altitude or so-called declination.
The instrument just described, perfected as to details but not modified
as to principles, constitutes the modern sextant, which is used by
every navigator, and which constitutes, along with the compass and
chronometer, the practical instrumental equipment that enables the
seaman to determine--by using the tables of the _Nautical Almanac_--his
exact position on the earth's surface from observation of the sun or
certain of the fixed stars. The modern instrument is called a sextant
because it has, for convenience' sake, been restricted in size to about
one-sixth of a circle instead of the original one-quarter, the small
size being found to answer every practical purpose, since it measures
all angles up to 120 degrees.
In practice the sextant is an instrument only six or eight inches in
diameter. It is held in the right hand and the movable radial arm is
adjusted with the left hand with the aid of a micrometer screw, and
the reading of the scale is made accurate by the vernier arrangement.
The ordinary observation--which every traveler has seen a navigator
make from the ship's bridge just at midday--is carried out by holding
the sextant in a vertical position directly in line of the sun, and
sighting the visible horizon line, meantime adjusting the recording
apparatus so as to keep the sun's limb seemingly in touch with the
horizon. As the sun is constantly shifting its position the vernier
must be constantly adjusted until the observation shows that the sun is
at the very highest point. The instrument being clamped and the scale
read, the latitude may be known when proper correction has been made
for the so-called dip, for refraction, and where great accuracy is
required for parallax.
[Illustration: "TAKING THE SUN" WITH THE SEXTANT.
The instrument is held in the right hand, and levelled at the horizon;
the left hand manipulating the micrometer screw which adjusts the
radial arm carrying the index mirror (at top of figure). The result is
read on the Vernier scale (arc at bottom of figure) with the aid of the
magnifying glass.]
Dip, it may be explained, is due to the fact that the observation is
made not from the surface of the water but from an elevation, which
is greater or less according to the height of the bridge, and which
therefore varies with each individual ship. The error of refraction
is due to the refraction of the sun's light in passing through the
earth's atmosphere, and will vary with the temperature and the degree
of atmospheric humidity, both of which conditions must be taken into
account. The amount of refractive error is very great if an object
lies near the horizon. Everyone is familiar with the oval appearance
of the rising or setting sun, which is due to refraction. With the sun
at the meridian, the refractive error is comparatively slight; and
when a star is observed at the zenith the refractive error disappears
altogether.
By parallax, as here employed, is meant the error due to the difference
in the apparent position of the sun as viewed by an observer at any
point of the earth's surface from what the apparent position would
be if viewed from the line of the center of the earth, from which
theoretical point the observations are supposed to be made. In the case
of bodies so distant as the sun, this angle is an exceedingly minute
one, and in the case of the fixed stars it disappears altogether. The
sun's parallax is very material indeed from the standpoint of delicate
astronomical observations, but it may be ignored altogether by the
practical navigator in all ordinary observations. There is one other
correction that he must make, however, in case of sun observations;
he must add, namely, the amount of semi-diameter of the sun to his
observed measurement, as all calculations recorded in the _Nautical
Almanac_ refer to the center of the sun's disk.
PERFECTING THE CHRONOMETER
The observation of the sun's height, with the various corrections just
suggested, suffices by itself to define the latitude of the observer.
Something more is required, however, before he can know his longitude.
How to determine this, was a problem that long taxed the ingenuity of
the astronomer. The solution came finally through the invention of the
chronometer, which is in effect an exceedingly accurate watch.
Time measurers of various types have, of course, been employed from the
earliest times. The ancient Oriental and Classical nations employed
the so-called clepsydra, which consisted essentially of receptacles
from or into which water dripped through a small aperture, the lapse of
time being measured by the quantity of water. At an undetermined later
date sand was substituted for the water, and the hour glass with which,
in some of its forms, nearly everyone is familiar, came into use. For
a long time this remained a most accurate of time measurers, though
efforts were early made to find substitutes of greater convenience.
Then clocks operated by weights and pulleys were introduced; and,
finally, after the time of the Dutchman Huygens, the pendulum clock
furnished a timepiece of great reliability. But the mechanism operated
by weight or pendulum is obviously ill-adapted to use on shipboard.
Portable watches, in which coiled springs took the place of the
pendulum, had indeed been introduced, but the mechanical ingenuity
of the watchmaker could not suffice to produce very dependable
time-keepers. The very idea of a watch that would keep time accurately
enough to be depended upon for astronomical observations intended to
determine longitude was considered chimerical.
Nevertheless the desirability of producing a portable time-keeper
of great accuracy was obvious, and the efforts of a large number
of experimenters were directed towards this end in the course of
the eighteenth century. These efforts were stimulated by the hope
of earning a prize of twenty thousand pounds offered by the British
Government for a watch sufficiently accurate to determine the
location of a ship with maximum error of half a degree, or thirty
nautical miles, corresponding to two minutes of time, in the course
of a transatlantic voyage. It affords a striking illustration of the
relative backwardness of nautical science, and of the difficulties
to be overcome, to reflect that no means then available enabled the
navigator at the termination of a transatlantic voyage to be sure of
his location within the distance of thirty nautical miles by any means
of astronomical or other observation known to the science of the time.
The problem was finally solved by an ingenious British carpenter
named John Harrison, who devoted his life to the undertaking, and
who came finally to be the most successful of watchmakers. Harrison
first achieved distinction by inventing the compensating pendulum--a
pendulum made of two metals having a different rate of expansion under
the influence of heat, so adjusted that change in one was compensated
by a different rate of change in the other. Up to the time of this
discovery, even the best of pendulum clocks had failed of an ideal
degree of accuracy owing to the liability to change of length of the
pendulum--and so, of course, to corresponding change in the rate of
its oscillation--with every alteration of temperature. Another means
of effecting the desired compensation was subsequently devised by Mr.
Graham, through the use of a well of mercury in connection with the
pendulum, so arranged that the expansion of the mercury upward in its
tube would compensate the lengthening of the pendulum itself under
effect of heat, and vice versa; but the Harrison pendulum, variously
modified in design, remains in use as a highly satisfactory solution of
the problem.
Harrison early conceived the idea that it might be possible to apply
the same principle to the balance-wheel of the watch. This problem
presented very great practical difficulties, but by persistent effort
these were finally overcome, and a balance-wheel produced, which, owing
to the unequal expansion and contraction of its two component metals
under changing temperature, altered its shape and so maintained its
rate of oscillation almost--though never quite--regardless of changing
conditions of temperature.
In 1761 Harrison produced a watch which was tested on a British ship
in a trip to the West Indies in that and the succeeding year, and
which proved to be a time-keeper of hitherto unexampled accuracy. The
inventor had calculated that the watch, when carried into the tropics,
would vary its speed by one second per day with each average rise
of ten degrees of temperature. Making allowance for this predicted
alteration, it was found that the watch was far within the limits of
variation allowed by the conditions of the test above outlined. It had
varied indeed only five seconds during the journey across the ocean.
On the return trip the watch was kept in a place near the stern of
the ship, for the sake of dryness, where, however, it was subjected
to a great deal of joggling, which led to a considerably greater
irregularity of action; but even so its variation on reaching British
shores was such as to cause a maximum miscalculation of considerably
less than thirty nautical miles.
Although Harrison seemed clearly enough to have won the prize,
there were influences at work that interfered for a time with full
recognition of his accomplishment. Presently he received half the
sum, however, and ultimately, after having divulged the secret of his
compensating balance and proved that he could make other watches of
corresponding accuracy, he received the full award.
Minor improvements have naturally been made in the watch since that
time, but the essential problem of making a really reliable portable
timepiece was solved by the compensating balance-wheel of Harrison.
The ship's chronometer of to-day is merely a large watch, with an
escapement of particular construction, mounted on gimbals so that it
will maintain a practically horizontal position.
Modern ships are ordinarily provided with at least three of these
time-keepers in order that each may be compared with the others, and
a more accurate determination of the time made than would be possible
from observation of a single instrument; inasmuch as no absolutely
accurate time-keeper has ever been constructed. Two chronometers would
obviously be not much better than one, since there would be no guide as
to whether any variation between them had been caused by one running
too fast or the other too slowly. But with a third chronometer to check
the comparison, it is equally obvious that a dependable clue will be
given as to the exact time.
It is to be understood of course that the variation of any of the
chronometers will be but slight if they are good instruments. Moreover
the tendency to vary in one direction or the other of each individual
instrument will be known from previous tests. Such tests are constantly
made at the Royal Observatory in England and elsewhere, and the
best chronometers bear certificates as to their accuracy and as to
their rate of variation. It may be added that a chronometer or other
timepiece is technically said to be a perfect instrument, not when
it has no variation at all--since this has proved an unattainable
ideal--but when its variation is slight, is always in one direction,
and is perfectly or almost perfectly uniform.
FINDING THE TIME WITHOUT A CHRONOMETER
In the reference made above to the testing of Harrison's watch, it
was stated that that instrument varied by only a certain number of
seconds in the course of the westerly voyage across the Atlantic, and
that its variation was somewhat greater on the return voyage. This
implies, clearly, that some method was available to test the watch in
the West Indies, without waiting for the return to England. At first
thought this may cause no surprise, since the local time can of course
be known anywhere through meridian observations; but on reflection
it may seem less and less obvious as to just what test was available
through which the exact difference in time between Greenwich, at
which the watch was originally tested, and local time at the station
in the West Indies could be determined. There are, however, several
astronomical observations through which this could be accomplished, and
in point of fact the comparative times and hence the precise longitudes
at many points on the Western Hemisphere--and indeed of all portions
of the civilized globe--were accurately known before the day of the
chronometer.
One of the simplest and most direct means of testing the time of a
place, as compared with Greenwich time, is furnished by observation
of the occultation of one of the moons of Jupiter. By occultation is
meant, as is well known, the eclipse of the body through passing into
the shadow of its parent planet. This phenomenon, causing the sudden
blotting out of the satellite as viewed from the earth, occurs at
definite and calculable periods and is obviously quite independent
of any terrestrial influence. It occurs at a given instant of time
and would be observed at that instant by any mundane witness to whom
Jupiter was at that time visible. If then an observer noted the exact
local time at which occultation occurred, and compared this observed
time with the Greenwich time at which such occultation was predicted
to occur, as recorded in astronomical tables, a simple subtraction
or addition will tell him the difference in time between his station
and the meridian at Greenwich; and this difference of time can be
translated into degrees of longitude by merely reckoning fifteen
degrees for each hour of time, and fractions of the hour in that
proportion.
It will be noted that this observation has value for the purpose
in question only in conjunction with certain tables in which the
movements of Jupiter and its satellite are calculated in advance. This
is equally true of the various other observations through which the
same information may be obtained--as for example, the observation of a
transit of Mars, or the measurement of apparent distance between the
moon and a given fixed star. Before the tables giving such computations
were published it was quite impossible to determine the exact longitude
of any transatlantic place whatsoever. We have already pointed out that
Columbus had only a vague notion as to how far he had sailed when he
discovered land in the West. The same vagueness obtained with all the
explorations of the immediately ensuing generations.
It was not until about the middle of the sixteenth century that
Mercator and his successors brought the art of map-making to
perfection; and the celebrated astronomical tables of the German Mayer,
which served as the foundation for calculations of great importance
to the navigator, were not published until 1753. The first _Nautical
Almanac_, in which all manner of astronomical tables to guide the
navigator were included, was published at the British Royal Observatory
in 1767.
At the present time, a navigator would be as likely to start on a
voyage without compass and sextant as without charts and a _Nautical
Almanac_. Indeed were he to overlook the latter the former would
serve but a vague and inadequate purpose. Yet, as just indicated, this
invaluable adjunct to the equipment of the navigator was not available
until well toward the close of the eighteenth century. But of course
numerous general tables had been in use long before this, else--to
revert to the matter directly in hand--it would not have been possible
to make the above-recorded test in the case of Harrison's famous watch
in the voyage of 1761-62.
ASCERTAINING THE SHIP'S LONGITUDE
In the days before the chronometer was perfected, almost numberless
methods of attempting to determine the longitude of a ship at sea were
suggested. There were astronomers who advocated observation of the
eclipse of Jupiter's satellites; others who championed the method of
so-called lunars--that is to say, calculation based on observation of
the distance of the moon at a given local time from one or another of
certain fixed stars arbitrarily selected by the calculator. Inasmuch as
the seaman could always regulate even a faulty watch from day to day
by observation of the meridian passage of the sun, it was thought that
these observations of Jupiter's satellite or of the moon would serve
to determine Greenwich time and therefore the longitude at which the
observation was made with a fair degree of accuracy. But in practice
it is not easy to observe the eclipse of Jupiter's satellite without a
fair telescope; and it was soon found that the tables for calculating
the course of the moon were by no means reliable, hence theoretically
excellent methods of determining longitude by observation of that body
proved quite unreliable in practice.
It was with the chief aim of bettering our knowledge of the moon's
course through long series of very accurate observations that the Royal
Observatory at Greenwich was founded. Perhaps it was not unnatural
under these circumstances that certain of the Astronomers Royal should
have advocated the method of lunars as the mainstay of the navigator.
In particular Maskelyne, who was in charge of the Observatory in
the latter part of the eighteenth century, was so convinced of
the rationality of this method that he was led to discredit the
achievements of Harrison's watches, and for a long time to exert an
antagonistic influence, which the watchmaker resented bitterly and it
would appear not without some show of reason.
Ultimately, however, the accuracy of the watch, and its
indispensableness in the perfected form of the chronometer, having been
fully demonstrated, the method of lunars became practically obsolete
and the mariner was able to determine his longitude with the aid of
sextant, chronometer, and _Nautical Almanac_, by means of direct
observation of the altitude of the sun by day and of sundry fixed stars
by night, a much simpler calculation sufficing than was required by the
older method.
As the sun is the chief time-measurer, whose rate of passage in a
seeming circumnavigation of the heavens is recorded by the dial of
clock, watch, or chronometer, it would seem as if the simplest
possible method of determining longitude would be found through
observation of the sun's meridian passage. The user of the sextant on
shipboard always makes, if weather permits, a meridian observation
of the sun, and such observation gives him an accurate gauge of the
altitude of the sun at its highest point and hence of his own latitude.
By adjusting the arm of the sextant with which this observation is
made, the observer is able to determine the exact point reached by the
sun in its upward course with all requisite accuracy.
But, unfortunately for his purpose, the sun does not poise for an
instant at the apex of its upward flight and then begin its descent. On
the contrary, its orbit being circular, the course of the sun just at
its highest point is approximately horizontal for an appreciable length
of time, and while the observer therefore has adequate opportunity to
measure with accuracy the highest point reached, he cannot possibly
make sure, within the limits of a considerable fraction of a minute, as
to the precise moment when the center of the sun is on the meridian. He
can, indeed, determine this point with sufficient accuracy for rough
calculations, but modern navigation demands something more than rough
calculations, inasmuch as a variation in time of one minute represents
one-quarter of a degree of longitude, or fifteen nautical miles at the
equator, and such uncertainty as this would imply can by no means be
permitted in the safe navigation of a ship that may be passing through
the water at the rate of a nautical mile in less than three minutes.
It follows that meridian observation of the sun, owing to the necessary
inaccuracy of such observation, is not the ideal method. In point of
fact the sun may be observed for this purpose to much better advantage
when it is at a considerable distance from the meridian, since then
its altitude above the horizon at a given moment is the only point
necessary to be determined. The calculation by which the altitude of
the sun may be translated into longitude is indeed more complicated
in this case; but while spherical trigonometry is involved in the
calculation, the tables supplied by the _Nautical Almanac_ enable the
navigator to make the estimate without the use of any knowledge beyond
that of the simplest mathematics.
MEASURING A DEGREE OF LATITUDE
While these observations tell the navigator his exact location in
degrees of latitude and longitude, such knowledge does not of course
reveal the distance traversed unless the precise length of the degree
itself is known; and this obviously depends upon the size of the
earth. Now we have seen that the earth was measured at a very early
date by Greek and Roman astronomers, but of course their measurements,
remarkable though they were considering the conditions under which
they were made, were but rough approximations of the truth. Numerous
attempts were made to improve upon these early measurements, but it
was not until well into the seventeenth century that a really accurate
measurement was made between two points on the earth's surface, the
difference between which, as measured in degrees and minutes, was
accurately known.
In June of the year 1633, the Englishman Robert Norman made very
accurate observations of the altitude of the sun on the day of the
summer solstice (when of course it is at its highest point in the
heavens); the observation being made with a quadrant several feet
in diameter stationed at a point near the Tower of London. On the
corresponding day of the following year he made similar observations at
a point something like 125 miles south of London, in Surrey. The two
observations determined the exact difference in latitude between the
two points in question.
Norman then undertook a laborious survey, that he might accurately
measure the precise distance in miles and fractions thereof that
corresponded to these known degrees of latitude. He made actual
measurements with the chain for the most part, but in a few places
where the topography offered peculiar difficulties he was obliged to
depend upon the primitive method of pacing.
The modern surveyor, equipped with instruments for the accurate
measuring of angles, not differing largely in principle from the
quadrant of the navigator, would consider Norman's method of
measurement a very clumsy one. He would measure only a single original
base line of any convenient length, but would make that measurement
with very great accuracy, using, perhaps, a rod packed in ice that
it might not vary in length by even the fraction of an inch through
changes in temperature. An accurate base line thus secured, he
would depend thereafter on the familiar method of triangulation, in
which angles are measured very accurately, and from such measurement
the length of the sides of the successive triangles determined by
simple calculation. In the end he would thus have made the most
accurate determination of the distance involved, without having
actually measured any portion thereof except the original base line.
Notwithstanding the crudity of Norman's method, however, his estimate
of the actual length of a degree of the earth's surface was correct,
as more recent measurements have demonstrated, within twelve yards--a
really remarkable result when it is recalled that the total length of
the degree is about sixty nautical miles.
Inasmuch as the earth is not precisely spherical, but is slightly
flattened at the poles, successive degrees of latitude are not
absolutely uniform all along a meridian, but decrease slightly as the
poles are approached. The deviation is so slight, however, that for
practical purposes the degree of latitude may be considered as an
unvarying unit. But obviously such is not the case with a degree of
longitude. The most casual glance at a globe on which the meridian
lines are drawn, shows that these lines intersect at the poles, and
that the distance between them is, in the nature of the case, different
at each successive point between poles and equator. It is only at the
equator itself that a degree of longitude represents 1/360 of the
earth's circumference. Everywhere else the parallels of latitude cut
the meridians in what are termed small circles--that is to say, circles
that do not represent circumference lines in the plane of the earth's
center. Therefore while all points on any given meridian of longitude
are equally distant in terms of degrees and minutes of arc from the
meridian of Greenwich, the actual distances from that meridian of the
different points as measured in miles will depend entirely upon their
latitude.
At the equator each degree of longitude corresponds to (approximately)
sixty miles, but in the middle latitudes traversed for example by the
transatlantic lines, a degree of longitude represents only half that
distance; and in the far North the meridians of longitude draw closer
and closer together until they finally converge, and at the poles all
longitudes are one.
It follows, then, that the navigator must always know both his latitude
and his longitude in order to estimate the exact distance he has
sailed. We have seen that a single instrument, the sextant, enables
him to make the observations from which both these essentials can be
determined. We must now make further inquiry as to the all important
guide without the aid of which his observations, however accurately
made, would avail him little. This guide, as already pointed out, is
found in the set of tables known as the _Nautical Almanac_.
THE NAUTICAL ALMANAC
Had the earth chanced to be poised in space with its axis exactly at
right angles to its plane of revolution, many computations of the
astronomer would be greatly simplified. Again, were the planetary
course circular instead of elliptical, and were the earth subject to
no gravitational influences except that of the sun and moon, matters
of astronomical computation would be quite different from what they
are. But as the case stands, the axis of the earth is not only tipped
at an angle of about twenty-three degrees, but is subject to sundry
variations, due to the wobbling of the great top as it whirls.
Then the other planets, notably the massive Jupiter, exert a perverting
influence which constantly interferes with the regular progression of
the earth in its annual tour about the sun. A moment's reflection makes
it clear that the gravitation pull of Jupiter is exerted sometimes in
opposition to that of the sun, whereas at other times it is applied in
aid of the sun, and yet again at various angles. In short, on no two
successive days--for that matter no two successive hours or minutes--is
the perturbing influence of Jupiter precisely the same.
What applies to the earth applies also, of course, to the varying
action of Jupiter on the moon and to the incessantly varied action of
the moon itself upon the earth. All in all, then, the course of our
globe is by no means a stable and uniform one; though it should be
understood that the perturbations are at most very slight indeed as
compared with the major motions that constitute its regular action and
lead to the chief phenomena of day and night and the succession of the
seasons.
Relatively slight though the perturbations may be, however, they are
sufficient to make noteworthy changes in the apparent position of the
sun and moon as viewed with modern astronomical instruments; and they
can by no means be ignored by the navigator who will determine the
position of his ship within safe limits of error. And so it has been
the work of the practical astronomers to record thousands on thousands
of observations, giving with precise accuracy the location of sun,
moon, planets, and various stars at given times; and these observations
have furnished the basis for the elaborate calculations of the
mathematical astronomers upon which the tables are based that in their
final form make up the _Nautical Almanac_, to which we have already
more than once referred.
These calculations take into account the precise nature of the
perturbing influences that are exerted on the earth and on the moon
on any given day, and hence lead to the accurate prediction as to the
exact relative positions of these bodies on that day. Stated otherwise,
they show the precise position in the heavens which will be held at
any given time by the sun for example, or by the important planets,
as viewed from the earth. How elaborate these computations are may be
inferred from the statement that the late Professor Simon Newcomb used
about fifty thousand separate and distinct observations in preparing
his tables of the sun. Once calculated, however, these tables of
Professor Newcomb are so comprehensive as to supply data from which the
exact position of the sun can be found for any day between the years
1200 B.C. and 2300 A.D., a stretch of some thirty-five centuries.
Such a statement makes it clear how very crude and vague the
deductions must have been from the observations of navigators, however
accurately made, prior to the time when such tables as those of the
_Nautical Almanac_ had been prepared. Fully to appreciate this, it
is necessary to understand that the observations supplied in such
profusion for the use of the mathematical astronomer are in themselves
subject to errors that might seriously vitiate the results of the final
computation. They must, therefore, be made with the utmost accuracy,
and with instruments specially prepared for the purpose. The chief
of these instruments is not the gigantic telescope but the small
and relatively simple apparatus known as a transit instrument. This
constitutes essentially a small telescope poised on very carefully
adjusted trunnions, in such a way that it revolves in a vertical
axis, bringing into view any celestial body that is exactly on the
meridian, and bodies in this position only. To make observation of
the transit--that is to say the passage across the meridian line--of
any given body more accurate, the transit instrument has stretched
vertically across the center of its field of vision a spider web, or a
series of parallel spider webs; in order, in the latter case, that the
mean time of several observations may be taken.
So exceedingly difficult is it to manufacture and mount an instrument
of requisite nicety of adjustment, that the effort has almost baffled
the ingenuity of the mechanic. Sir George Airy, in making a transit
instrument for use at the Royal Observatory at Greenwich, required the
trunnions on which it was to be mounted to be ground truly cylindrical
in form within a variation of one thirty-two-thousandth of an inch
as determined by a delicate spirit level. Even when all but absolute
decision has been obtained, however, it is quite impossible to maintain
it, as the slightest variation of temperature--due perhaps to the
application of the hand to one of the pillars on which the trunnions
rest--may disturb the precise direction of the spider webs and so
militate against absolute accuracy of observation. The instrument must,
therefore, be constantly tested and its exact range of errors noted and
allowed for.
To devote so much labor to details, merely in the effort to determine
the precise moment at which a star or planet crosses the meridian,
would seem to be an absurd magnification of trifles. But when we
reflect that the prime object of such observations is to supply
practical data which will be of service in enabling navigators on all
the seas of the globe to bring their ships safely to port, the matter
takes on quite another aspect. We have here, obviously, another and
a very striking illustration of the close relationship that obtains
between the work of the theoretical devotee of science and that of the
practical man of affairs.
SOUNDINGS AND CHARTS
Though the navigator, thanks to his compass, sextant, and _Nautical
Almanac_, may determine with a high degree of precision his exact
location, yet even the best observations do not enable him to approach
a coast without safeguarding his ship by the use of another piece of
mechanism calculated to test the depth of the waters in which he finds
himself at any given moment. In its most primitive form--in which form,
by the bye, it is still almost universally employed--this apparatus is
called the lead,--so called with much propriety because it consists
essentially of a lump of lead or other heavy weight attached to a small
rope. Knots in the rope enable the sailor who manipulates the lead to
note at a glance the depth to which it sinks. Most ocean travelers have
seen a sailor heaving the lead repeatedly at the side of the ship and
noting the depth of the water, particularly as the ship approached the
Long Island shore.
While this simple form of lead suffices for ordinary purposes, when
the chief information sought is as to whether the water is deeper than
the draft of the ship, it is at best only a rough and ready means of
testing the depth in relatively shallow waters. For deeper waters and
to test with greater accuracy the depths of uncharted regions, and in
particular to determine the character of the sea bottom at any given
place, more elaborate apparatuses are employed. One of the most useful
of these is the invention of the late Lord Kelvin. In this the lead
is replaced by a cannon ball, perforated and containing a cylinder
which is detached when the weight reaches the bottom and is drawn to
the surface filled with sand or mud, the cannon ball remaining at the
bottom. In another form of patent lead, a float becomes detached so
soon as the weight strikes the bottom and comes at once to the surface,
thus recording the fact that the bottom has been reached,--a fact not
always easy to appreciate by the mere feel of the line when the water
is fairly deep.
It is obvious that however well informed the navigator may be as to
his precise latitude and longitude, he can feel no safety unless he
is equally well informed as to the depth of the water, the proximity
of land, the presence or absence of shallows in the region, and the
like. He must, therefore, as a matter of course, be provided with maps
and charts on which these things are recorded. From the days when
navigation first became a science, unceasing efforts have been made
to provide such maps and charts for every known portion of the globe.
Geographical surveys, with the aid of the method of triangulation, have
been made along all coasts, and elaborate series of soundings taken for
a long distance from the coast line, and there are now few regions into
which a ship ordinarily sails, or is likely to be carried by accident,
for which elaborate charts, both of coast lines and of soundings, have
not been provided. The experienced navigator is able to direct his ship
with safety along coasts that he visits for the first time, or to enter
any important harbor on the globe without requiring the services of a
local pilot,--albeit the desire to take no undue risk makes it usual to
accept such services.
Time was, however, when maps and charts were not to be had, and when
in consequence the navigator who started on his voyages of exploration
was undertaking a feat never free from hazard. Until the time of
Mercator there was not even uniformity of method among map makers in
the charting of regions that had been explored. The thing seems simple
enough now, thanks to the maps with which every one has been familiar
since childhood. But it required no small exercise of ingenuity to
devise a reasonably satisfactory method of representing on a flat
surface regions that in reality are distributed over the surface of a
globe. The method devised by Mercator, and which, as everyone knows, is
now universally adopted, consists in drawing the meridians as parallel
lines, giving therefore a most distorted presentation of the globe, in
which the distance between the meridians at the poles--where in reality
there is no distance at all--is precisely as great as at the equator.
To make amends for this distortion, the parallels of latitude are not
drawn equidistant, as in reality they practically are on the globe, but
are spaced farther and farther apart, as we advance from the equator
toward either pole. The net result is that an island in the arctic
region would be represented on the map several times as large as an
island actually the same size but located near the equator. Doubtless
most of us habitually conceive Alaska and Greenland to be vastly more
extensive regions than they really are, because of our familiarity with
maps showing this so-called "Mercator's projection."
Of course maps are also made that hold to the true proportions,
representing the lines of latitude as equidistant and the meridians of
longitude as lines converging to a point at the poles. But while such
a map as this has certain advantages--giving, for example, a correct
notion of the relative sizes of polar and other land masses--it is
otherwise confusing inasmuch as places that really lie directly in
the north and south line cannot be so represented except just at the
middle of the map, and it is very difficult for the ordinary user of
the map to gain a clear notion as to the actual points of the compass.
A satisfactory compromise may be effected, however, by using Mercator's
projection for maps showing wide areas, while the other method is
employed for local maps.
THE LURE OF THE UNKNOWN
While the average man, even with well developed traveling instincts,
would perhaps prefer always to feel that he is sailing in well charted
waters and along carefully surveyed coasts, there have been in every
generation men who delighted in taking risks, and for whom half the
charm of a voyage must always lie in its dangers. Such men have been
the pioneers in exploring the new regions of the globe. That there was
no dearth of such restless spirits in classical times and even in the
dark ages, records that have come down to us sufficiently attest. For
the most part, however, their names have not been preserved to us. But
since the ushering in of the period which we to-day think of as the
beginning of modern times, records have been kept of all important
voyages of discovery, and at least the main outlines of the story of
the conquest of the zones are familiar to everyone.
Some of the earliest explorers, most notable among whom was the
Italian Marco Polo, traveled eastward from the Mediterranean and
hence journeyed largely by land. But soon afterward, thanks to
the introduction of the compass,--which instrument Marco Polo has
sometimes been mistakenly accredited with bringing from the East,--the
adventurers began to cast longing eyes out toward the western
horizons. Among the first conspicuous and inspiriting results were the
discoveries of the groups of islands known as the Cape Verdes and the
Azores. The Canary Islands were visited by Spaniards even earlier, and
became the subject of controversy with the other chief maritime nation
of the period, the Portuguese.
When the controversy was adjusted the Spaniards were left in possession
of the Canaries, but the Portuguese were given by treaty the exclusive
right to explore the coast of Africa. Following up sundry tentative
efforts, the daring Portuguese navigator, Bartholomeo Dias, in the
year 1487, passed to the southern-most extremity of Africa, which he
christened the Cape of Good Hope. At last, then, it had been shown
that Africa did not offer an interminable barrier to the passage to
the fabled land of treasures in the East. Before anyone had ventured
to follow out the clues which the discovery of the Cape had presented,
however, Columbus had seemingly solved the problem in another way by
sailing out boldly into the West and supposedly coming to the East
Indies in 1492.
The western route was barred to the Portuguese but the eastern one
remained open to them, and before the close of the century Vasco da
Gama had set out on the voyage that ultimately led him to India by way
of the Cape (1497-1500 A.D.). Twenty years later another Portuguese
navigator, Magellan by name, started on what must ever remain the most
memorable of voyages, save only that of Columbus. Magellan rounded the
southern point of South America and in 1521 reached the Philippines,
where he died. His companions continued the voyage and accomplished
ultimately the circumnavigation of the globe; and in so doing afforded
the first unequivocal practical demonstration, of a character
calculated to appeal to the generality of uncultured men of the time,
that the world is actually round.
Two routes from Europe to the Indies had thus been established, but
both of them were open to the objection that they necessitated long
detours to the South. To the geographers of the time it seemed more
than probable that a shorter route could be established by sailing
northward and coasting along the shores either of Europe to the East
or--what seemed more probable--of America to the West. Toward the
close of the sixteenth century the ships of the Dutch navigators had
penetrated to Nova Zembla, and a few years later Henry Hudson visited
Spitzbergen, thus inaugurating the long series of arctic expeditions.
Then Hudson, still sailing under the Dutch flag, made heroic efforts to
find the fabled northwest passage, only to meet his doom in the region
of the Bay that has since borne his name.
THE QUEST OF THE POLE
This was in the year 1610. For long generations thereafter successors
of Hudson were to keep up the futile quest; and when finally it
had been clearly established that no northwest passage to the
Pacific could be made available, owing to the climate, the zest for
arctic exploration did not abate, but its goal was changed from the
hypothetical northwest passage to the geographical pole.
Henry Hudson had in his day established a farthest North record of
about the eighty-second parallel of latitude--leaving only about five
hundred miles to be traversed. But three centuries were required in
which to compass this relatively small gap. Expedition after expedition
penetrated as far as human endurance under given conditions could carry
it. Some of the explorers returned with vivid tales of the rigors of
the arctic climate; others fell victim to conditions that they could
not overcome. But the seventeenth, eighteenth, and nineteenth centuries
passed and left the "Boreal Center" undiscovered.
Toward the close of the nineteenth century the efforts of explorers
seemed to be redoubled and one famous expedition after another
established new records of "farthest North." The names of Nansen, the
Duke of the Abruzzi, and Peary, became familiar to a generation whose
imagination seemed curiously in sympathy with that lure of the North
which determined the life activities of so many would-be discoverers.
So when in the early Autumn of 1909 it was suddenly announced that two
explorers in succession had at last, in the picturesque phrasing of one
of them, "penetrated the Boreal Center and plucked the polar prize,"
the popular mind was stirred as it has seldom been by any other event
not having either a directly personal or an international political
significance.
The two men whose claims to have discovered the pole were thus
announced in such spectacular fashion, were Dr. Frederick A. Cook,
of Brooklyn, and Lieutenant Commander Robert E. Peary, of the United
States Navy. Dr. Cook claimed to have reached the pole, accompanied
only by two Eskimo companions, on the twenty-first day of April, 1908.
Commander Peary reported that he had reached the pole, accompanied by
Mr. Matthew H. Henson and four Eskimos, on the seventh day of April,
1909.
The controversy that ensued regarding the authenticity of these
alleged discoveries is not likely to be forgotten by any reader of our
generation. Its merits and demerits have no particular concern for the
purely scientific inquirer. At best, as Professor Pickering of Harvard
is reported to have said, "the quest of the pole is a good sporting
event" rather than an enterprise of great scientific significance. It
suffices for our present purpose, therefore, to know that Dr. Cook's
records, as adjudged by the tribunal of the University of Copenhagen,
to which they were sent, were pronounced inadequate to demonstrate the
validity of his claim; whereas Peary and Henson were adjudged by the
American Geographical Society, after inspection of the records, to have
accomplished what was claimed for them. What has greater interest from
the present standpoint is the question, which the controversy brought
actively to the minds of the unscientific public, as to how tests are
made which determine, in the mind of the explorer himself, the fact of
his arrival at the pole.
The question has, indeed, been largely answered in the earlier pages
of this chapter, in our discussion of the sextant and the _Nautical
Almanac_; for these constitute the essential equipment of the arctic
explorer no less than of the navigators of the seas of more accessible
latitudes. There is one important matter of detail, however, that
remains to be noted. This relates to the manner of using the sextant.
On the ocean, as we have seen, the navigator levels the instrument at
the visible horizon; but it is obvious that on land or on the irregular
ice fields of the arctic seas no visible horizon can be depended upon
as a basis for measuring the altitude of sun or stars. So an artificial
horizon must be supplied.
The problem is solved by the use of a reflecting surface, which may
consist of an ordinary mirror or a dish of mercury. The glass reflector
must be adjusted in the horizontal plane with the aid of spirit levels;
mercury, on the other hand, being liquid, presents a horizontal surface
under the action of gravitation. Unfortunately mercury freezes at
about 39 degrees below zero; it is therefore often necessary for the
arctic explorer to melt it with a spirit lamp before he can make use
of it. These, however, are details aside from which the principles of
use of glass and mercury horizon are identical. The method consists
simply in viewing the reflected image of the celestial body--which in
practice in the arctic regions is usually the sun--and so adjusting the
sextant that the direct image coincides with the reflected one. The
angle thus measured will represent twice the angular elevation of the
body in question above the horizon,--this being, as we have seen, the
information which the user of the sextant desires.
Of course the explorer makes his "dash for the pole" in a season when
the sun is perpetually above the horizon. As he approaches the pole the
course of the sun becomes apparently more and more nearly circular,
departing less and less from the same altitude. Hence it becomes
increasingly difficult to determine by observation the exact time when
the sun is at its highest point. But it becomes less and less important
to do so as the actual proximity of the pole is approached; and as
viewed from the pole itself the sun, circling a practically uniform
course, varies its height in the course of twenty-four hours only
by the trifling amount which represents its climb toward the summer
solstice. Such being the case, an altitude observation of the sun may
be made by an observer at the pole at any hour of the day with equal
facility, and it is only necessary for him to know from his chronometer
the day of the month in order that he may determine from the _Nautical
Almanac_ whether the observation really places him at ninety degrees of
latitude. Nor indeed is it necessary that he should know the exact day
provided he can make a series of observations at intervals of an hour
or two. For if these successive observations reveal the sun at the same
altitude, it requires no _Almanac_ and absolutely no calculation of any
kind to tell him that his location is that of the pole.
The observation might indeed be made with a fair degree of accuracy
without the use of the sextant or of any astronomical equivalent
more elaborate than, let us say, an ordinary lead pencil. It is only
necessary to push the point of the pencil into a level surface of ice
or snow and leave it standing there in a vertical position. If, then,
the shadow cast by the pencil is noted from time to time, it will be
observed that its length is always the same; that, in other words,
the end of the shadow as it moves slowly about with the sun describes
a circle in the course of twenty-four hours. If the atmospheric
conditions had remained uniform, so that there was no variation in the
amount of refraction to which the sun's rays were subjected, the circle
thus described would be almost perfect, and would in itself afford a
demonstration that would appeal to the least scientific of observers.
An even more simple demonstration might be made by having an Eskimo
stand in a particular spot and marking the length of his shadow as cast
on a level stretch of ice or snow. Just twelve hours later let the
Eskimo stand at the point where a mark had been made to indicate the
end of the shadow, and it would be found that his present shadow--cast
now, of course, in the opposite direction--would reach exactly to the
point where he had previously stood. The only difficulty about this
simple experiment would result from the fact that the sun is never
very high as viewed from the pole and therefore the shadow would
necessarily be long. It might therefore be difficult to find a level
area of sufficient extent on the rough polar sea. In that case another
measurement similar in principle could be made by placing a pole
upright in the snow or ice and marking on the pole the point indicated
by the shadow of an Eskimo standing at any convenient distance away.
At any interval thereafter, say six or twelve hours, repeat the
experiment, letting the man stand at the same distance from the pole as
before, and his shadow will be seen to reach to the same mark.
Various other simple experiments of similar character may be devised,
any of which would appeal to the most untutored intelligence as
exhibiting phenomena of an unusual character. Absolutely simple as
these experiments are, they are also, within the limits of their
accuracy, absolutely demonstrative. There are only two places on the
globe where the shadow of the upright pencil would describe a circle,
or where the man's shadow would be of the same length at intervals of
twelve hours, or would reach to the same height on a pole in successive
hours. These two regions are of course the poles of the earth. It may
reasonably be expected that explorers who reach the poles will make
some such experiments as these for the satisfaction of their untrained
associates, to whom the records of the sextant would be enigmatical.
But for that matter even an Eskimo could make for himself a measurement
by using only a bit of a stick held at arm's length--as an artist
measures the length of an object with his pencil--that would enable
him to make reasonably sure that the sun was at the same elevation
throughout the day--subject, however, to the qualification that the
polar ice was sufficiently level to provide a reasonably uniform
horizon.
While, therefore, it appears that the one place of all others at which
it would be exceedingly easy to determine one's position from the
observation of the sun is the region of the pole, it must be borne in
mind that the low elevation of the sun, and the extreme cold may make
accurate instrumental observations difficult; and it is conceivable
that the explorer who had the misfortune to encounter cloudy weather,
and who therefore gained only a brief view of the sun, might be left
in doubt as to whether he had really reached the goal of his ambition.
Fortunately, however, the explorers who thus far claim to have reached
the pole record uninterruptedly fair weather, enabling observations to
be taken hour after hour. Under these circumstances, there could be no
possibility of mistake as to the general location, although perhaps no
observation, under the existing conditions, could make sure of locating
the precise position of the pole within a few miles.
A curious anomaly incident to the unique geographical location of
the pole is that to the observer stationed there all directions are
directly south. Yet of course all directions are not one, and the query
may arise as to how an explorer who has reached the pole may know in
what direction to start on his return voyage. The answer is supplied
by the compass, which--perforce pointing straight south--indicates the
position of the magnetic pole and so makes clear in which direction
lies the coast of Labrador. Moreover if the explorer is provided with
reliable chronometers, which of course record the time at a given
meridian--say that of Greenwich--these will enable him to determine by
the simplest calculation what particular region lies directly beneath
the sun at any given time. If, for example, his chronometer shows five
o'clock Greenwich time, he knows that the sun's position, as observed
at the moment, marks the meridian five hours (_i.e._, 75° of longitude)
west of Greenwich.
While the arctic region appears thus to have given up its last secret,
this is not as yet true of the antarctic. The expedition of Lieutenant
(now Sir Ernest) Shackleton, in 1908, approached within about one
hundred and eleven miles of the South Pole. The intervening space--less
than two degrees in extent--represents, therefore, the only stretch of
latitude on the earth's surface that has not been trodden by man's foot
or crossed by his ships. More than one expedition is being planned to
explore this last remaining stronghold, and in all probability not many
years--perhaps not many months--will elapse before the little stretch
of ice that separated Lieutenant Shackleton from the South Pole will be
crossed, and man's conquest of the zones will be complete.
II
THE HIGHWAY OF THE WATERS
There is no doubt that the use of sails for propelling boats is as old
as civilization itself. We know that the Egyptians used sails at least
4,000 years before the Christian era. They did not depend entirely upon
the sails, however, but used oars in combination with them. Steering
was done with single or double oars lashed to the stern and controlled
by ropes or levers. This method of steering remained in use until late
in the Middle Ages, the invention of the rudder being one of the few
nautical inventions made during the centuries immediately following
that unproductive period of history known as the Dark Age.
Following the Egyptians, the Phœnicians were the greatest maritime
nation of ancient times, but unfortunately they have left no very
satisfactory and authentic records describing their boats. In all
probability, however, their ships were galleys having one or two banks
of oars, fitted with sails similar to those of the Egyptians.
If our knowledge of Phœnician boats is meager, our knowledge of Greek
boats, particularly the fighting craft, is correspondingly full. From
the nature of its geographical location Greece was necessarily a
maritime nation, and it was here that boat-building reached a very
high state of development during the period of Greek predominance.
Large ships fitted with sails and having several banks of rowers were
used habitually in commerce and war, and it was here also that the
management of sails became so well understood that oars were often
dispensed with except as auxiliaries.
It was in Greece that the custom of having several banks of oars
superimposed reached its highest development, but the fabulous number
of such banks credited by some authors seems to be entirely without
foundation. It is possible that as many as seven banks were used,
although the evidence in favor of more than five is very slight.
The writings of Callixenos describe a ship said to have been used by
Ptolemy Philopater, which was a forty-banker. This ship is described as
450 feet long, 57 feet broad, carrying a crew of about 7,000 men, of
whom 4,000 were rowers. This description need not be taken seriously,
as there is no proof that boats of such proportions were ever attempted
in ancient times. But it is certain that the Greeks did build large
vessels, some of them at least one hundred and fifty feet long--perhaps
even larger than this. The tendency of shipbuilders during the later
Greek period was to build large, unwieldy boats, which used sails
under favorable circumstances, but depended entirely upon oars for
manœuvering in battle.
The Romans used similar vessels of large size until the time of the
battle of Actium, where the clumsy, many-banked ships of Antony and
Cleopatra were destroyed by the lighter single- or double-banked
vessels of Augustus. Augustus had adopted the low, swift, handy vessels
of a piratical people, the Liburni, who had learned in their sea fights
against all kinds of vessels that the lighter type of boat could be
used most effectively. Structurally the hulls of these boats were not
unlike modern wooden vessels.
While the various types of vessels were being developed in the
Mediterranean region, a race of mariners far to the north were
perfecting boats in which they were destined to overrun the Western
seas from the tropics to the arctic circle. These people, the Norsemen,
left few written descriptions that give a good idea of the construction
of their boats, which were sufficiently seaworthy to enable the Danes
to cross the Atlantic and colonize America. But thanks to one of their
peculiar burial customs some of their smaller boats have been preserved
and brought to light in recent years. It was their custom when a great
chief died, to bury him in a ship, heaping earth over it to form a
great mound. In most instances the wood of such boats, buried for a
thousand years, has entirely disappeared; but in some mounds the boats
have been preserved almost intact.
From the specimens so preserved it is known that the Norsemen knew
how to shape the hulls of their boats almost as well as the modern
boat-builder. This fact is interesting because the immediate successors
of the Norsemen, either through ignorance or choice, reverted to most
primitive types in building their boats. Thus it required centuries for
them to develop a knowledge of hull-construction that was familiar in
ancient times to the northern rovers. Scandinavia itself never entirely
forgot the art, and there are boats built in Norway to-day closely
similar in all essentials to some of the boats constructed by the
Norsemen.
MEDIÆVAL SHIPS
The contrast in shape and construction between the trim ships of the
Norsemen and the short, top-heavy vessels which were the approved
European type during the early Middle Ages, is most striking. The
Mediæval shipbuilders in striving to improve their craft, making them
as seaworthy and as spacious as possible, first added decks, and then
built towering superstructures at bow and stern. The result was a
vessel which would have been so top-heavy that it would be likely to
capsize had it not been so broad that "turning turtle" was out of the
question.
It was in such ships that Columbus made his voyage of discovery in
1492, although the superstructures fore and aft on his boat were
less exaggerated than in some later vessels. Nevertheless they were
veritable "tubs"; and we know from the experience of the crew that
sailed the replica of the _Santa Maria_ across the ocean in 1893, that
they were anything but comfortable craft for ocean traveling.
This replica of the _Santa Maria_ was reproduced with great fidelity
by the Spanish shipbuilders, and, manned by a Spanish crew, crossed
the ocean on a course exactly following that taken by Columbus on his
first voyage. Sir George Holmes' terse description of this voyage is
sufficiently illuminating without elaboration. "The time occupied was
thirty-six days," he says; "and the maximum speed attained was about 6½
knots. The vessel pitched horribly!"
Two full centuries before the discovery of America the rudder had
been invented. There is no record to show who was responsible for
this innovation, although its superiority over the older steering
appliances must have been appreciated fully. But after the beginning of
the fourteenth century the rudder seems to have come into general use,
entirely supplanting the older side-rudder, or clavus.
MODERN SAILING SHIPS
For a full century after the voyage of Columbus little progress was
made in ship construction; short, stocky boats, with many decks high
above the water-line at bow and stem continuing to be the most popular
type. In the opening years of the seventeenth century, however,
the English naval architect, Phineas Pett, departed from many of
the accepted standards of his time, and produced ships not unlike
modern full-rigged sailing vessels, except that the stern was still
considerably elevated, and the bow of peculiar construction. One of
Pett's ships, _The Sovereign of the Seas_, was a vessel 167 feet long,
with 48 foot beam, and of 1,683 tons burthen. The introduction of this
type of vessel was a distinct step forward toward modern shipbuilding.
[Illustration: THE OLD AND THE NEW--A CONTRAST
The replica of Henry Hudson's famous _Half Moon_, a typical fighting
ship of the 16th century, and a modern submarine. The photograph
was taken in New York Harbor during the Hudson-Fulton celebration,
September, 1909.]