OBSERVATIONS.
In sketching out a system of observation having especial reference to
atmospheric waves and rotatory storms, regard has been had--_first_, to
the instruments that should be used, the observations to be made with
them, the corrections to be applied to such observations, and the form
of registry most suitable for recording the results: _second_, to the
times of observation: _third_, to the more important localities that
should be submitted to additional observation: _fourth_, to peculiar
phænomena requiring extraordinary observations for their elucidation:
and _fifth_, to particular seasons, when the instruments should be
watched with more than ordinary care.
The more important objects of observation having especial reference to
atmospheric waves are those points which have been termed _crests_ and
_troughs_. These are simply the _highest_ and _lowest_ readings of the
barometer, usually designated _maxima_ and _minima_, and should for the
object in view receive particular attention. Whenever there is reason to
believe that the barometer is approaching either a _maximum_ or
_minimum_, additional observations should be resorted to, so as to
secure as nearly as possible _the precise time_ as reckoned at the ship,
with her position, of its occurrence, as well as the altitude of the
mercurial column at that time and place. By means of such observations
as these on board several ships scattered over the surfaces of our great
oceans, much valuable information may be accumulated of a character
capable of throwing considerable light on the _direction_ in which the
lines of barometric maxima and minima stretch, and also a tolerably
accurate notion may be formed of their progress, both as regards
direction and rate. In immediate connexion with such observations
particular attention should be paid to the direction of the wind
according to the season.
SECTION I.--INSTRUMENTS.
_Description and Position of Instruments._--The principal instrument
requisite in these observations is the barometer, which should be of the
marine construction, and as nearly alike as possible to those furnished
to the Antarctic expedition which sailed under the command of Sir James
Clark Ross. These instruments were similar to the ordinary portable
barometers, and differed from them only in the mode of their suspension
and the necessary contraction of the tubes to prevent oscillation from
the motion of the ship. The barometer on shipboard should be suspended
on a gimbal frame, which ought not to swing too freely, but rather so as
to deaden oscillations by some degree of friction. To the upper portion
of the tube in this construction of instrument light is alike accessible
either in front or behind, and the vernier is furnished with a back and
front edge, both being in precisely the same plane, nearly embracing the
tube, and sliding up and down it by the motion of rack-work; by the
graduation of the scale and vernier the altitude of the mercury can be
read off to ·002 inch.
When the barometer is placed in the ship, its position should be as near
midships as possible, out of the reach of sunshine, but in a good light
for reading, and in a situation in which it will be but little liable to
sudden gusts of wind and changes of temperature. Great care should be
taken to ascertain the exact height of its cistern above the water-line,
and in order to facilitate night observations every possible arrangement
should be made for placing behind it a light screened by white paper.
_Observations._--The first thing to be done is the reading off and
recording the temperature indicated by the thermometer that in this
construction of instrument dips into the mercury in the cistern. Sir
John Herschel has suggested that "the bulb of the thermometer should be
so situated as to afford the best chance of its indicating the exact
mean of the whole barometric column, that is to say, fifteen inches
above the cistern enclosed within the case of the barometer, nearly in
contact with its tube, and with a stem so long as to be read off at the
upper level."
Previous to making an observation with the barometer the instrument
should be slightly tapped to free the mercury from any adhesion to the
glass; any violent oscillation should, however, be carefully avoided.
The vernier should then be adjusted to the upper surface of the mercury
in the tube; for this purpose its back and front edges should be made to
coincide, that is, the eye should be placed in exactly the same plane
which passes through the edges; they should then be brought carefully
down until they form a tangent with the curve produced by the convex
surface of the mercury and the light is _just_ excluded from between
them and the point of contact. It is desirable in making this adjustment
that the eye should be assisted by a magnifying-glass. The reading of
the scale should then be taken and entered in the column appropriated to
it in the proper form. If the instrument have no tubular or double-edged
index, the eye should be placed carefully at the level of the upper
surface of the mercury and the index of the vernier brought gently down
to the same level so as apparently just to touch the surface, great care
being taken that the eye index and surface of the mercury are all in the
same plane.
Each observation of the barometer should be accompanied by an
observation of the direction of the wind, which should be noted in the
usual manner in which it is observed at sea. In connexion with the
_direction_ the _force_ of the wind should be recorded in accordance
with the following scale, contrived by Admiral Sir Francis Beaufort:--
0. Calm
1. Light air or just sufficient to give steerage way.
2. Light breeze { or that in which a well- } 1 to 2 knots.
3. Gentle breeze { conditioned man of war, } 3 to 4 knots.
4. Moderate breeze { with all sail set, and } 5 to 6 knots.
{ clean full, would go in }
{ smooth water, from }
5. Fresh breeze } { Royals, &c.
6. Strong breeze } { Single-reefed top-sails
} { and top-gallant
} or that in which such a { sails.
7. Moderate gale } ship could just carry in { Double-reefed
} chase full and by { topsails, jib, &c.
8. Fresh gale } { Triple-reefed
} { topsails, &c.
9. Strong gale } { Close-reefed top-sails
} { and courses.
10. Whole gale or that with which she could scarcely bear
close-reefed main topsail and reefed foresail.
11. Storm or that which reduces her to storm staysails.
12. Hurricane or that which no canvas could withstand.
_Corrections._--As soon after the observations have been made as
circumstances will permit, the reading of the barometer should be
_corrected_ for the relation existing between the capacities of the tube
and cistern (if its construction be such as to require that correction),
and for the capillary action of the tube; and then _reduced_ to the
standard temperature of 32° Fahr., and to the sea-level, if on
shipboard. For the first correction the _neutral point_ should be marked
upon each instrument. It is that particular height which, in its
construction, has been actually measured from the surface of the mercury
in the cistern, and indicated by the scale. In general the mercury will
stand either above or below the neutral point; if _above_, a portion of
the mercury must have left the cistern, and consequently must have
_lowered_ the surface in the cistern: in this case the altitude as
measured by the scale will be _too short--vice versâ_, if below. The
relation of the capacities of the tube and cistern should be
experimentally ascertained, and marked upon the instrument by the maker.
Suppose the capacity to be 1/50, marked thus on the instrument,
"_Capacity 1/50:_" this indicates that for every inch of variation of
the mercury in the tube, that in the cistern will vary contrariwise
1/50th of an inch. When the mercury in the tube is _above_ the neutral
point, the difference between it and the neutral point is to be reduced
in the proportion expressed by the "capacity" (in the case supposed,
divided by 50), and the quotient _added_ to the observed height; if
_below, subtracted_ from it. In barometers furnished with a fiducial
point for adjusting the lower level, this correction is superfluous, and
must not be applied.
The second correction required is for the capillary action of the tube,
the effect of which is always to depress the mercury in the tube by a
certain quantity inversely proportioned to the diameter of the tube.
This quantity should be experimentally determined during the
construction of the instrument, and its amount marked upon it by the
maker, and is always to be _added_ to the height of the mercurial
column, previously corrected as before. For the convenience of those who
may have barometers, the capillary action of which has not been
determined, a table of corrections for tubes of different diameters is
placed in the Appendix, Table I.
The next correction, and in some respects the most important of all, is
that due to the temperature of the mercury in the barometer tube at the
time of observation, and to the expansion of the scale. Table II. of the
Appendix gives for every degree of the thermometer and every half-inch
of the barometer, the proper quantity to be added or subtracted for the
reduction of the observed height to the standard temperature of the
mercury at 32° Fahr.
After these the index correction should be applied. This is the amount
of difference between the particular instrument and the readings of the
Royal Society's flint-glass barometer when properly corrected, and is
generally known as the _zero_. It is impossible to pay too much
attention to the determination of this point. For this purpose, when
practicable, the instrument should be immediately compared with the
Royal Society's standard, and the difference of the readings of both
instruments, when corrected as above, carefully noted and preserved.
Where, however, this is impracticable, the comparison should be effected
by means either of some other standard previously so compared, or of an
intermediate portable barometer, the zero point of which has been _well
determined_. Suspend the portable barometer as near as convenient to the
ship's barometer, and after at least an hour's quiet exposure, take as
many readings of both instruments as may be necessary to reduce the
probable error of the mean of the differences below 0.001 inch. Under
these circumstances the mean difference of all the readings will be the
_relative_ zero or index error, whence, if that of the intermediate
barometer be known, that of the other may be found. As such comparisons
will always be made when the vessel is in port, sufficient time can be
allowed for making the requisite number of observations: hourly readings
would perhaps be best, and they would have the advantage of forming part
of the system when in operation, and might be accordingly used as such.
It is not only desirable that the zero point of the barometer should be
well determined in the first instance; it should also be carefully
verified on every opportunity which presents itself; and in every
instance, previous to sailing, it should be re-compared with the
standard on shore by the intervention of a portable barometer, and no
opportunity should be lost of comparing it on the voyage by means of
such an intermediate instrument with the standard barometers at St.
Helena, the Cape of Good Hope, Bombay, Madras, Paramatta, Van Diemen's
Island, and with any other instruments likely to be referred to as
standards, or employed in research elsewhere. Any vessel having a
portable barometer on board, the zero of which has been well determined,
would do well, on touching at any of the ports above named, to take
comparative readings with the standards at those ports, and record the
differences between the standard, the portable, and the ship barometers.
By such means the zero of one standard may be transported over the whole
world, and those of others compared with it ascertained. To do so,
however, with perfect effect, will require that the utmost care should
be taken of the portable barometer; it should be guarded as much as
possible from all accident, and should be kept safely in the "portable"
state when not immediately used for comparison. To transport a
well-authenticated zero from place to place is by no means a point of
trifling importance. Neither should it be executed hurriedly nor
negligently. Some of the greatest questions in meteorology depend on its
due execution, and the objects for which these instructions have been
prepared will be greatly advanced by the zero points of all barometers
being referred to one common standard. Upon the arrival of the vessel in
England, at the termination of the voyage, the ship's barometer should
be again compared with the same standard with which it was compared
previous to sailing; and should any difference be found, it should be
most carefully recorded.
The correction for the height of the cistern _above_ or _below_ the
water-line is _additive_ in the former case, _subtractive_ in the
latter. Its amount may be taken, nearly enough, by allowing 0·001 in. of
the barometer for each foot of difference of level.
An example of the application of these several corrections is
subjoined:--
| _Attached Therm_. 54°·3. |_Data for the correction of |
| | the Instrument_. |
+---------------------------------------+-------------------------------+
|Barometer reading. 29·409 |Neutral point 30·123 |
|Corr. for capacity - ·017 |Capacity 1/42 |
| |Capillary action + ·032 |
+---------------------------------------| |
| 29·392 |Zero to Royal Society + ·036 |
|Corr. for capillarity + ·032 |Corr. for altitude above |
| | water-line + ·004 |
+---------------------------------------| |
| 29·424 | |
|Corr. for temperature - ·068 | |
+---------------------------------------| |
| 29·356 | |
|Corr. for zero and water-line + ·040 | |
+---------------------------------------| |
|Aggregate = pressure at | |
| sea-level 29·396 | |
+---------------------------------------+-------------------------------+
It would greatly facilitate the comparison of the barometric
observations by projecting them in curves when all the proper
corrections have been applied. This may be accomplished by a much
smaller expenditure of time than may at first be supposed. A paper of
engraved squares on which the observations of twelve days may be laid
down on double the natural scale, would be very suitable for the
purpose.[4] The projection of each day's observations would occupy but a
short time; and should circumstances on any occasion prevent the
execution of it, when the ship was becalmed or leisure otherwise
afforded, it would form an interesting and useful occupation, and serve
to beguile some of the tedium often experienced at such intervals.
_Registers._--For the particular object in view the register need not be
very extensive. One kept in the annexed form will be amply sufficient.
It should, however, be borne in mind that none but _uncorrected_
observations should find admission; in point of fact it should be
strictly a register of phænomena as _observed_, and on no account
whatever should any entry be made from recollection, or any attempt made
to fill up a blank by the apparent course of the numbers before and
after. The headings of the columns will, it is hoped, be sufficiently
explicit. It is desirable in practice that the column for remarks should
embrace an entire page opposite the other entries, in order that
occasional observations, as well as several other circumstances
continually coming under review in the course of keeping a journal, may
find entry.
METEOROLOGICAL REGISTER kept on board ______ during her voyage from
______ to ______ by ______.
+---------+----+------+-------+------+------------------+--------+----------+
| | | | | | Wind. | | |
| | | | | Att. |-----------+------| | |
| Date. |Lat.| Long.| Barom.| Ther.| Direction.|Force.| Remarks| Observer.|
|---------|----|------|-------|------|-----------|------|--------|----------|
| |h. m.| | | | | | | | |
| | | | | | | | | | |
| | | | | | | | | | |
| | | | | | | | | | |
| | | | | | | | | | |
| | | | | | | | | | |
+---+-----+----+------+-------+------+-----------+------+--------+----------+
The only difference between the above form and one for the reception of
_corrected_ readings will be the dispensing with the column for the
attached thermometer, and placing under the word Barom. "corrected."
II.--TIMES OF OBSERVATION.
There can be no question that the greatest amount of information, the
accuracy of the data supplied, and in fact every meteorological element
necessary to increase our knowledge of atmospheric waves, may be best
obtained by an uninterrupted series of _hourly_ observations made on
board vessels from their leaving England until their safe arrival again
at the close of their respective voyages; but from a variety of
circumstances--the nature of the service in which the vessels may be
employed, particular states of the weather, &c.--such a course of
unremitting labour cannot be expected; it is therefore necessary to fix
on some stated hours at which the instruments before particularized
should be regularly observed throughout the voyage, and their
indications faithfully recorded. The hours of 3 A.M., 9 A.M., 3 P.M.,
and 9 P.M., are now so generally known as _meteorological hours_, that
nothing should justify a departure from them; and it is the more
essential that these hours should be adopted in the present inquiry,
because the series of observations made at intervals terminated by these
hours can the more readily be used in connexion with those made
contemporaneously on land, and will also serve to carry on
investigations previously instituted, and which have received
considerable illustration by means of observations at the regular
meteorological hours; we therefore recommend their general adoption in
all observations conducted at sea.
It is intended in the sequel to call attention to particular parts of
the earth's surface where it is desirable that additional observations
should be made, in order to furnish data of a more accurate character,
and to mark more distinctly barometric changes than the four daily
readings are capable of effecting. The best means of accomplishing this
for the object in view appears to be the division of the interval of six
hours into two equal portions, and to make the necessary observations
eight times in the course of twenty-four hours. In the particular
localities to which allusion has been made we recommend the following as
the hours of observation:--
A.M. 3, 6, 9, noon. P.M. 3, 6, 9, midnight.
In other localities besides those hereafter to be mentioned, when
opportunities serve, readings at these hours would greatly enhance the
value of the four daily readings.
There are, however, portions of the surface of our planet, and probably
also phænomena that occur in its atmosphere, which require still closer
attention than the eight daily readings. One such portion would appear
to exist off the western coast of Africa, and we recommend the adoption
of _hourly_ readings while sailing to the westward of this junction of
aqueous and terrestrial surface; more attention will be directed to this
point as we proceed. There are also phænomena the localities of which
may be undetermined, and the times of their occurrence unknown, but so
important a relation do they bear to the subject of our inquiries, that
they demand the closest attention. They will be more particularly
described under the head of accumulations of pressure preceding and
succeeding storms, and minute directions given for the hourly
observations of the necessary instruments. In the mean time we may here
remark that hourly observations under the circumstances above alluded to
are the more important when we consider that the barometer, the
instrument employed in observing these moving atmospheric masses, is
itself in motion. The ship may meet the accumulation of pressure and
sail through it transversely; or she may sail along it, the course of
the vessel being parallel to the line marking the highest pressure, the
ridge or crest of the wave; or the ship may make any angle with this
line: but whatever the circumstances may be under which she passes
through or along with such an accumulation of pressure, it should ever
be borne in mind that her position on the earth's surface is scarcely
ever the same at any one observation as it was at the preceding, the
barometer in the interval has changed _its_ position as well as the line
of maximum pressure, the rate of progress of which it is desirable to
observe. It will, therefore, be at once apparent that in order to obtain
the most accurate data on this head hourly observations are
indispensable. To these readings should of course be appended the places
of the ship from hour to hour, especially if she alter her course much.
There is another point to which we wish to call attention in immediate
connexion with hourly readings--it is the observation of the instruments
on the days fixed for that purpose: they were originally suggested by
Sir John Herschel, whose directions should be strictly attended to: they
are as follows:--
The days fixed upon for these observations are the 21st of March, the
21st of June, the 21st of September, and the 21st of December, being
those, or immediately adjoining to those of the equinoxes and
solstices, in which the _solar influence_ is either stationary or in a
state of most rapid variation. _But should any one of those 21st days
fall on a Sunday, then it will be understood that the observations are
to be deferred till the next day, the 22nd._ The series of observations
on board each vessel should commence at 6 o'clock A.M. of the appointed
days, and terminate at 6 A.M. of the days following, according to the
usual reckoning of time adopted in the daily observations.
In addition to the twenty-five hourly readings at the solstices and
equinoxes as above recommended, it would be desirable to continue the
observations until a complete elevation and depression of the barometer
had been observed at these seasons. This plan is adopted at the Royal
Observatory, Greenwich, and would be attended with this advantage were
it generally so--the progress of the elevation and depression would be
more readily traced and their velocities more accurately determined than
from the four or eight daily readings.
III.--LOCALITIES FOR ADDITIONAL OBSERVATIONS.
In sketching out a system of barometric observation having especial
reference to the acquisition of data from which the _barometric
character_ of certain large areas of the surface of the globe may be
determined--inasmuch as such areas are distinguished from each other, on
the one hand by consisting of extensive spaces of the oceanic surface
unbroken, or scarcely broken, by land; on the other by the proximity of
such oceanic surface to large masses of land, and these masses
presenting two essentially different features, the one consisting of
land particularly characterized as continental, the other as insular,
regard has been accordingly had to such distribution of land and water.
As these instructions have especial reference to observations at sea,
observations on land have not been alluded to; but in order that the
data accumulated may possess that value which is essential for carrying
on the inquiry in reference to atmospheric waves with success, provision
is made to mark out more distinctly the barometric effects of the
junction of large masses of land and water. It is well known that the
oceanic surface, and even the smaller surfaces of inland seas, produce
decided inflexions of the isothermal lines. They exercise an important
influence on temperature. It has also been shown that the neighbourhood
of water has a very considerable influence in increasing the
oscillations of the mercurial column in the barometer, and in the great
systems of European undulations it is well known that these oscillations
increase especially towards the north-west. The converse of this,
however, has not yet been subjected to observation; there has been no
systematic co-operation of observers for the purpose of determining the
barometric affections of large masses of water, such as the central
portion of the basin of the northern Atlantic, the portion of oceanic
surface between the Cape of Good Hope and Cape Horn, the Indian and
Southern oceans, and the vast basin of the Pacific. Nor are we yet
acquainted with the character of the oscillations, whether increasing or
decreasing, as we recede from the central portions of the oceanic
surfaces we have mentioned towards the land which forms their eastern,
western, or northern boundaries. This influence of the junction line of
land and water, so far as it is yet known, has been kept in view in
framing these instructions, and, as it appears so prominently in Europe,
it is hoped the additional observations between the four daily readings
to which probably many observers may habitually restrict themselves,
making on certain occasions and in particular localities a series of
observations at intervals of three hours, will not be considered too
frequent when the great importance of the problem to be solved is fully
apprehended. It need scarcely be said that the value of these
observations at three-hourly intervals will be greatly increased by the
number of observers co-operating in them. Upon such an extensive system
of co-operation a large space on the earth's surface, possessing
peculiarities which distinguish it from others extremely unlike it in
their general character, or assimilate it to such as possess with it
many features in common, is marked out below for particular observation,
occupying more than two-thirds of a zone in the northern hemisphere,
having a breadth of 40°, and including every possible variety of
terrestrial and aqueous surface, from the burning sands of the great
African desert, situated about the centre, to the narrow strip of land
connecting the two Americas on the one side, and the chain of islands
connecting China and Hindostan with Australia on the other. On each side
of the African continent we have spaces of open sea between 30° and 40°
west longitude north of the equator, and between 60° and 80° east
longitude, in or to the south of the equator, admirably suited for
contrasting the barometric affections, as manifested in these spaces of
open water, with those occurring in situations where the influence of
the terrestrial surface comes into more active operation.
The localities where three-hourly readings are chiefly desirable may be
specified under the heads of _Northern Atlantic, Southern Atlantic,
Indian_ and _Southern Oceans,_ and _Pacific Ocean_.
_Northern Atlantic. Homeward-bound Voyages._--The discussion of
observations made in the United Kingdom and the western border of
central Europe, has indicated that off the north-west of Scotland a
centre of great barometric disturbance exists. This centre of
disturbance appears to be considerably removed from the usual tracks of
vessels crossing the Atlantic; nevertheless some light may be thrown on
the barometric phænomena resulting from this disturbance by observations
during homeward-bound voyages, especially after the vessels have passed
the meridian of 50° west longitude. Voyagers to or from Baffin and
Hudson bays would do well during the whole of the voyage to read off the
barometer every three hours, as their tracks would approach nearest the
centre of disturbance in question. Before crossing the 50th meridian,
the undulations arising from the distribution of land and water in the
neighbourhood of these vast inland seas would receive considerable
elucidation from the shorter intervals of observation, and after passing
the 50th meridian the extent of undulation, as compared with that
observed by the more southerly vessels, would be more distinctly marked
by the three-hourly series. Surveying vessels stationed on the
north-western coasts of Ireland and Scotland may contribute most
important information on this head by a regular and, as far as
circumstances will allow, an uninterrupted series either of six-hourly
or three-hourly observations. The intervals of observation on board
vessels stationed at the Western Isles, the Orkneys, and the Shetland
Isles, ought not to be longer than _three_ hours, principally on account
of the great extent of oscillation observed in those localities. Vessels
arriving from all parts of the world as they approach the United Kingdom
should observe at shorter intervals than six hours. As a general
instruction on this head the series of three-hourly observations may be
commenced on board vessels from America and the Pacific by the way of
Cape Horn on their passing the 20th meridian, such three-hourly
observations to be continued until the arrival of the vessels in port.
Ships by the way of the Cape of Good Hope should commence the
three-hourly series either on leaving or passing the colony, in order
that the phænomena of the tropical depression hereafter to be noticed
may be well observed.
_Northern Atlantic. Outward-bound Voyages_.--Vessels sailing to the
United States, Mexico, and the West Indies, should observe at three
hours' interval upon passing the 60th meridian. Observations at this
interval, on board vessels navigating the Gulf of Mexico and the
Caribbean Sea, will be particularly valuable in determining the extent
of oscillation as influenced by the masses of land and water in this
portion of the torrid zone, as compared with the oscillation noticed off
the western coast of Africa, hereafter to be referred to.
_Southern Atlantic. Outward and homeward bound_.--Without doubt the most
interesting phænomenon, and one that lies at the root of the great
atmospheric movements, especially those proceeding northwards in the
northern hemisphere and southwards in the southern, is the equatorial
depression first noticed by Von Humboldt and confirmed by many observers
since. We shall find the general expression of this most important
meteorological fact in the Report of the Committee of Physics and
Meteorology, appointed by the Royal Society in 1840, as follows: "The
barometer, at the level of the sea, does not indicate a mean atmospheric
pressure of equal amount in all parts of the earth; but, on the
contrary, the equatorial pressure is uniformly less in its mean amount
than at and beyond the tropics." Vessels that are outward bound should,
upon passing 40° north latitude, commence the series of three-hourly
observations, with an especial reference to the equatorial depression.
These three-hourly observations should be continued until the latitude
of 40° south has been passed: the whole series will then include the
minimum of the depression and the two maxima or apices forming its
boundaries. (See Daniell's 'Meteorological Essays,' 3rd edition.) In
passages across the equator, should the ships be delayed by calms,
opportunities should be embraced for observing this depression with
greater precision by means of _hourly_ readings; and these readings will
not only be valuable as respects the depression here spoken of, but will
go far to indicate the character of any disturbance that may arise, and
point out, as nearly as such observations will allow, the precise time
when such disturbance produced its effects in the neighbourhood of the
ships. In point of fact they will clearly illustrate the diversion of
the tendency to rise, spoken of in the Report before alluded to, as
resulting in ascending columns and sheets, between which wind flaws,
capricious in their direction and intensity, and often amounting to
sharp squalls, mark out the course of their feeders and the indraft of
cooler air from a distance to supply their void. Hourly observations,
with especial reference to this and the following head of inquiry,
should also be made off the western coast of Africa during the
homeward-bound voyage.
Immediately connected with this part of the outward-bound voyage, hourly
observations, as often as circumstances will permit, while the ships are
sailing from the Madeiras to the equator, will be extremely valuable in
elucidating the origin of the great system of south-westerly atmospheric
waves that traverse Europe, and in furnishing data for comparison with
the amount of oscillation and other barometric phænomena in the Gulf of
Mexico and the Caribbean Sea, a portion of the torrid zone essentially
different in its configuration and in the relations of its area to land
and water, as contra-distinguished to the northern portion of the
African continent; and these hourly observations are the more desirable
as the vessels may approach the land. They may be discontinued on
passing the equator, and the three-hourly series resumed.
There are two points in the southern hemisphere, between 80° west
longitude and 30° east longitude, that claim particular attention in a
barometric point of view, viz., Cape Horn and the Cape of Good Hope; the
latter is within the area marked out for the three-hourly observations,
and too much attention cannot be paid to the indications of the
barometer as vessels are approaching or leaving the Cape. The northern
part of the South Atlantic Ocean has been termed the _true Pacific Ocean
of the world_; and at St. Helena a gale was scarcely ever known; it is
also said to be entirely free from actual storms (Col. Reid's 'Law of
Storms,' 1st edition, p. 415). It may therefore be expected that the
barometer will present in this locality but a small oscillation, and
ships in sailing from St. Helena to the Cape will do well to ascertain,
by means of the three-hourly observations, the increase of oscillation
as they approach the Cape. The same thing will hold good with regard to
Cape Horn: it appears from previous observation that a permanent
barometric depression exists in this locality, most probably in some way
connected with the immense depression noticed by Captain Sir James Clark
Ross, towards the Antarctic Circle. The general character of the
atmosphere off Cape Horn is also extremely different from its character
at St. Helena. It would therefore be well for vessels sailing into the
Pacific by Cape Horn, to continue the three-hourly observations until
the 90th meridian is passed.
Before quitting the Atlantic Ocean it may be well to notice the marine
stations mentioned in my Third Report on Atmospheric Waves,[5] as being
particularly suitable for testing the views advanced in that report and
for tracing a wave of the south-westerly system from the most western
point of Africa to the extreme north of Europe. A series of hourly
observations off the western coast of Africa has already been suggested.
Vessels staying at Cape Verd Islands should not omit to make
observations at three hours' interval _during the whole of their stay_,
and when circumstances will allow, hourly readings. At the Canaries,
Madeiras, and the Azores, similar observations should be made. Vessels
touching at Cape Cantin, Tangier, Gibraltar, Cadiz, Lisbon, Oporto,
Corunna, and Brest, should also make these observations while they are
in the localities of these ports. At the Scilly Isles we have six-hourly
observations, made under the superintendence of the Honourable the
Corporation of the Trinity House. Ships in nearing these islands and
making the observations already pointed out, will greatly assist in
determining the increase of oscillation proceeding westward from the
nodal point of the two great European systems. We have already mentioned
the service surveying vessels employed on the coasts of Ireland and
Scotland may render, and the remaining portion of the area marked out in
the report may be occupied by vessels navigating the North Sea and the
coast of Norway, as far as Hammerfest.
In connexion with these observations, having especial reference to the
European system of south-westerly atmospheric waves, the Mediterranean
presents a surface of considerable interest, both as regards these
particular waves, and the influence its waters exert in modifying the
two great systems of central Europe. The late Professor Daniell has
shown from the Manheim observations, that small undulations, having
their origin on the northern borders of the Mediterranean, have
propagated themselves northward, and in this manner, but in a smaller
degree, the waters of the Mediterranean have contributed to increase the
oscillation as well as the larger surface of the northern Atlantic. In
most of the localities of this great inland sea six-hourly observations
may suffice for this immediate purpose; but in sailing from Lisbon
through the Straits of Gibraltar, in the neighbourhood of Sicily and
Italy, and in the Grecian Archipelago, we should recommend the
three-hourly series, as marking more distinctly the effects resulting
from the proximity of land; this remark has especial reference to the
passage through the Straits of Gibraltar, where, if possible, hourly
observations should be made.
_The Indian and Southern Oceans. Outward and homeward bound._--On
sailing from the Cape of Good Hope to the East Indies, China, or
Australia, observations at intervals of three hours should be made until
the 40th meridian east is passed (homeward-bound vessels should commence
the three-hourly readings on arriving at this meridian). Upon leaving
the 40th meridian the six-hourly observations may be resumed on board
vessels bound for the Indies and China until they arrive at the equator,
when the readings should again be made at intervals of three hours, and
continued until the arrival of the vessels in port. With regard to
vessels bound for Australia and New Zealand, the six-hourly readings may
be continued from the 40th to the 100th meridian, and upon the vessels
passing the latter, the three-hourly readings should be commenced and
continued until the vessels arrive in port. Vessels navigating the
Archipelago between China and New Zealand, should make observations
every three hours, in order that the undulations arising from the
configuration of the terrestrial and oceanic surfaces may be more
distinctly marked and more advantageously compared with the Gulf of
Mexico, the Caribbean Sea, and the northern portion of the African
continent.
_The Pacific Ocean._--As this ocean presents so vast an aqueous surface,
generally speaking observations at intervals of six hours will be amply
sufficient to ascertain its leading barometric phænomena. Vessels,
however, on approaching the continents of North and South America, or
sailing across the equator, should resort to the three-hourly readings,
in order to ascertain more distinctly the effect of the neighbourhood of
land on the oscillations of the barometer, as generally observed, over
so immense a surface of water in the one case, and the phænomena of the
equatorial depression in the other: the same remarks relative to the
latter subject, which we offered under the head of South Atlantic, will
equally apply in the present instance. The configuration of the western
shores of North America renders it difficult to determine the precise
boundary where the three-hourly series should commence; the 90th
meridian is recommended for the boundary as regards South America, and
from this a judgment may be formed as to where the three-hourly
observations should commence in reference to North America.
In the previous sketch of the localities for the more important
observations, it will be seen that within the tropics there are three
which demand the greatest regard.
I. The Archipelago between the two Americas, more particularly comprised
within the 40th and 120th meridians west longitude, and the equator and
the 40th degree of north latitude. As a general principle we should say
that vessels within this area should observe the barometer every three
hours. Its eastern portion includes the lower branches of the storm
paths, and on this account is peculiarly interesting, especially in a
barometric point of view.
II. _The Northern portion of the African Continent, including the Sahara
or Great Desert._--This vast radiating surface must exert considerable
influence on the waters on each side northern Africa. Vessels sailing
within the area comprised between 40° west and 70° east, and the equator
and the 40th parallel, should also make observations at intervals of
three hours.
III. _The great Eastern Archipelago._--This presents a somewhat similar
character to the western; like that, it is the region of terrific
hurricanes, and it becomes a most interesting object to determine its
barometric phænomena; the three-hourly system of observation may
therefore be resorted to within an area comprised between the 70th and
140th meridians, and the equator and the 40th degree of north latitude.
The southern hemisphere also presents three important localities, the
prolongations of the three tropical areas. It is unnecessary to enlarge
upon these, as ample instructions have been already given. We may,
however, remark, with regard to Australia, that three-hourly
observations should be made within the area comprised between the 100th
and 190th meridians east, and the equator and the 50th parallel south,
and hourly ones in the immediate neighbourhood of all its coasts.
IV.--STORMS, HURRICANES, AND TYPHOONS.
The solution of the question--How far and in what manner are storms
connected with atmospheric waves?--must be extremely interesting to
every one engaged in either the naval or merchant service. As we have in
the former chapters directed attention to their connexion, our great
object here will be to endeavour to mark out such a line of observation
as appears most capable of throwing light, not only on the most
important desiderata as connected with storms, but also their connexion
or non-connexion with atmospheric waves. We shall accordingly
arrange this portion of the instructions under the following
heads:--_Desiderata_; _Localities_; _Margins_; _Preceding and Succeeding
Accumulations of Pressure._
_Desiderata._--The most important desiderata appertaining to the subject
of storms, are certainly their origin and termination. Of these initial
and terminal points in the course of great storms we absolutely know
nothing, unless _the white appearance of a round form_ observed by Mr.
Seymour on board the Judith and Esther, in lat. 17° 19' north and long.
52° 10' west (see Col. Reid's 'Law of Storms,' 1st edit. p. 65), may be
regarded as the commencement of the Antigua hurricane of August 2, 1837.
This vessel was the most eastern of those from which observations had
been obtained; and it is the absence of contemporaneous observations to
the eastward of the 50th meridian that leaves the question as to the
origin of the West Indian revolving storms unsolved. Not one of Mr.
Redfield's storm routes extends eastward of the 50th meridian; this at
once marks out, so far as storms are concerned, the entire space
included between the 20th and 50th meridians, the equator and the 60th
parallel, as a most suitable area for observations, under particular
circumstances hereafter to be noticed, with especial reference either to
the commencement or termination of storms, or the prolongation of Mr.
Redfield's storm paths.
_Localities._--The three principal localities of storms are as
follows:--I. The western portion of the basin of the North Atlantic; II.
The China Sea and Bay of Bengal; and III. The Indian Ocean, more
particularly in the neighbourhood of Mauritius. The first two have
already been marked out as areas for the three-hourly observations; to
the latter, the remark as to extra observations under the head of
Desiderata will apply.
_Margins._--Mr. Redfield has shown that on some occasions storms have
been preceded by an unusual pressure of the atmosphere; the barometer
has stood remarkably _high_, and it has hence been inferred that there
has existed _around_ the gale an accumulation of air forming a margin;
barometers placed under this margin indicating a much greater pressure
than the mean of the respective localities. With regard to the West
Indian and American hurricanes--any considerable increase of pressure,
especially within the space marked out to the eastward of the 50th
meridian, will demand immediate attention. Upon the barometer ranging
_very high_ within this space, three-hourly observations should be
immediately resorted to; and if possible, _hourly_ readings taken, and
this is the more important the nearer the vessel may be to the 50th
meridian. Each observation of the barometer should be accompanied by an
observation of the wind--its direction should be most carefully noted,
and the force estimated according to the scale in page 21, or by the
anemometer. It would be as well _at the time_ to project the barometric
readings in a curve even of a rough character, that the extent of fall
after the mercury had passed its maximum might be readily discernible by
the eye. A paper ruled in squares, the vertical lines representing the
commencement of hours, and the horizontal tenths of an inch, would be
quite sufficient for this purpose. The _force_ of the wind should be
noted at, or as near to the time of the passage of the maximum as
possible. During the fall of the mercury particular attention should be
paid to the manner in which the wind changes, should any change be
observed; and should the wind continue blowing steadily in _one_
direction, but gradually _increasing_ in force, then such increments of
force should be most carefully noted. During the fall of the barometer,
should the changes of the wind and its increasing force indicate the
neighbourhood of a revolving storm, (independent of the obvious reasons
for avoiding the focus of the storm,) it would contribute as much to
increase our knowledge of these dangerous vortices to keep as near as
possible to their margins as to approach their centres. The recess from
the centre towards the margin of the storm, will probably be rendered
apparent by the _rising_ of the mercury; and so far as the observations
may be considered valuable for elucidating the connexion of atmospheric
waves with rotatory storms (other motives being balanced), it might be
desirable to keep the ship near the margin--provided she is not carried
beyond the influence of the winds which characterize the latter half of
the storm--until the barometer has nearly attained its usual elevation.
By this means some notion might be formed of the general direction of
the line of barometric pressure preceding or succeeding a storm.
Should a gale be observed commencing without its having been preceded by
an unusual elevation of the mercurial column, and consequently no
additional observation have been made; when the force of the wind is
noted in the usual observations at or above 5, then the three-hourly
series should be resorted to, and the same care taken in noting the
direction, changes, and force of the wind as pointed out in the
preceding paragraph.
The foregoing remarks relate especially to the central and western
portions of the North Atlantic; they will however equally apply to the
remaining localities of storms. Under any circumstances, and in any
locality, a _high_ barometer not less than a low one should demand
particular attention, and if possible, _hourly_ readings taken some time
before and after the passage of the maximum: this will be referred to
more particularly under the next head.
_Preceding and Succeeding Accumulations of Pressure._--Mr. Redfield has
shown in his Memoir of the Cuba Hurricane of October, 1844, that two
associated storms were immediately preceded by a barometric wave, or
accumulation of pressure, the barometer rising above the usual or annual
mean. We have just referred to the importance of _hourly_ observations
on occasions of the readings being _high_ as capable of illustrating the
marginal phænomena of storms, and in connexion with these accumulations
of pressure in advance of storms we would reiterate the suggestion.
These strips of accumulated pressure are doubtless crests of atmospheric
waves rolling forwards. In some cases a ship in its progress may cut
them transversely in a direction at right angles to their _length_, in
others very obliquely; but in all cases, whatever section may be given
by the curve representing the observations, too much attention cannot be
bestowed on the barometer, the wet and dry bulb thermometer, the
direction and force of the wind, the state of the sky, and the
appearance of the ocean during the ship's passage _through_ such an
accumulation of pressure. When the barometer attains its mean altitude,
and is rapidly rising above it in any locality, then _hourly_
observations of the instruments and phænomena above noticed should be
commenced and continued until after the mercury had attained its highest
point and had sunk again to its mean state. In such observations
particular attention should be paid to the direction and force of the
wind preceding the barometric maximum--and the same phænomena succeeding
it, and particular notice should be taken of the time when, and amount
of any change either in the direction or force of the wind. It is by
such observations as these, carried on with great care and made at every
accessible portion of the oceanic surface, that we may be able to
ascertain the continuity of these atmospheric waves, to determine
somewhat respecting their length, to show the character of their
connexion with the rotatory storm, and to deduce the direction and rate
of their progress.
V.--SEASONS FOR EXTRA OBSERVATIONS.
In reference to certain desiderata that have presented themselves in the
course of my researches on this subject (see Report of the British
Association for the Advancement of Science, 1846, p. 163), the _phases_
of the larger barometric undulations, and the _types_ of the various
seasons of the year, demand particular attention and call for extra
observations at certain seasons: of these, three only have yet been
ascertained--the type for the middle of November--the annual depression
on or about the 28th of November--and the annual elevation on or about
the 25th of December. The enunciation of the first is as under: "That
during fourteen days in November, more or less equally disposed about
the middle of the month, the oscillations of the barometer exhibit a
remarkably symmetrical character, that is to say, the fall succeeding
the transit of the maximum or the highest reading is to a great extent
similar to the preceding rise. This rise and fall is not continuous or
unbroken; in some cases it consists of _five_, in others of _three_
distinct elevations. The complete rise and fall has been termed the
great symmetrical barometric wave of November. At its setting in the
barometer is generally low, sometimes below twenty-nine inches. This
depression is generally succeeded by _two_ well-marked undulations,
varying from one to two days in duration. The central undulation, which
also forms the apex of the great wave, is of larger extent, occupying
from three to five days; when this has passed, two smaller undulations
corresponding to those at the commencement of the wave make their
appearance, and at the close of the last the wave terminates." With but
slight exceptions, the observations of eight successive years have
confirmed the general correctness of this type. On two occasions the
central apex has not been the highest, and these deviations, with some
of a minor character, form the exceptions alluded to. This type only has
reference to London and the south-eastern parts of England; proceeding
westward, north-westward, and northward, the symmetrical character of
this type is considerably departed from; each locality possessing its
own type of the barometric movements during November. The desiderata in
immediate connexion with the November movements, as observed in the
southern and south-eastern parts of England, that present themselves,
are--the determination of the types for November, especially its middle
portion, as exhibited on the oceanic surface within an area comprised
between the 30th and 60th parallels, and the 1st and 40th meridians
west. Vessels sailing within this area may contribute greatly to the
determination of these types by making observations at intervals of
three hours from the 1st of November to the 7th or 8th of December. The
entire period of the great symmetrical wave of November will most
probably be embraced by such a series of observations, as well as the
annual depression of the 28th. For the elevation of the 25th of December
the three-hourly observations should be commenced on the 21st, and
continued until the 3rd or 4th of the succeeding January.
With respect to the great wave of November, our knowledge of it would be
much increased by such a series of observations as mentioned above,
being made on board surveying and other vessels employed off Scotland
and Ireland; vessels navigating the North Sea; vessels stationed off the
coasts of France, Spain, Portugal, and the northern parts of Africa, and
at all our stations in the Mediterranean. In this way the area of
examination would be greatly enlarged, and the _differences_ of the
curves more fully elucidated; and this extended area of observation is
the more desirable, as there is some reason to believe that the line of
greatest symmetry _revolves_ around a fixed point, most probably the
nodal point of the great European systems.
It is highly probable that movements of a somewhat similar character,
although presenting very different curves, exist in the southern
hemisphere. The November wave is more or less associated with storms. It
has been generally preceded by a high barometer and succeeded by a low
one, and this low state of the barometer has been accompanied by stormy
weather. We are therefore prepared to seek for similar phænomena in the
southern hemisphere, in those localities which present similar states of
weather, and at seasons when such weather predominates. We have already
marked out the two capes in the Southern hemisphere for three-hourly
observations: they must doubtless possess very peculiar barometric
characters, stretching as they do into the vast area of the Southern
Ocean. It is highly probable that the oscillations, especially at some
seasons, are very considerable, and vessels visiting them at such
seasons would do well to record with especial care the indications of
the instruments already alluded to. At present we know but little of the
barometric movements in the Southern hemisphere, and every addition to
our knowledge in this respect will open the way to more important
conclusions.
It has been observed in the south-east of England that the barometer has
generally passed a maximum on or about the 3rd of every month, and this
has been so frequently the case as to form the rule rather than the
exception. The same fact during a more limited period has been observed
at Toronto. With especial reference to this subject the three-hourly
series of observations may be resorted to in all localities, but
especially north of the 40th parallel in the northern hemisphere. They
should be commenced at midnight immediately preceding the 1st and
continued to midnight succeeding the 5th.
CHAPTER IV.
PRACTICAL DIRECTIONS FOR AVOIDING THE CENTRES OF ROTATING
STORMS.
Figures 1 and 2, enlarged and printed on narrow rings of stiff
cardboard, are employed for this purpose. The letters outside the thick
circle are intended to distinguish the points of the compass, and in use
should always coincide with those points on the chart. The letters
within the thick circle indicate the direction of the wind in a
hurricane, the whirl being shown by the arrows between the letters. In
the northern hemisphere the direction of the whirl is always contrary to
that in which the hands of a watch move, and in the southern coincident
thereto. The graduation is intended to assist the mariner in
ascertaining the bearing of the centre of a storm from his ship.
_Use._
At any time when a severe gale or hurricane is expected, the seaman
should at once find the position of his ship on the chart, and place
upon it the graduated point which answers to the direction of the wind
at the time, taking care that the needle is directed to the north, so
that the exterior letters may point on the chart to the respective
points of the compass: this is very essential. This simple process will
at once acquaint the seaman with two important facts relative to the
coming hurricane--his position in the storm, and the direction in
which it is moving.
_Examples._
A captain of a ship in latitude 35° 24' N., longitude 64° 12' W., bound
to the United States, observes the barometer to stand unusually high,
say 30·55 inches: shortly after the mercury begins to fall, at first
slowly and steadily; as the glass falls the wind freshens, and is
noticed to blow with increasing force from the S. so as to threaten a
gale. The position of the ship on the chart is now to be found, and the
graduated point under the letters E. S. is to be placed thereon,
taking care to direct the needle to the north. From these two
circumstances, the falling barometer and the wind blowing from the south
with increasing force, the mariner is aware of this simple fact, that he
is situated in the advancing portion of a body of air which is
proceeding towards the N.E.; and if he turn his face to the N.E. he will
find he is on the right of the axis line, or line cutting the advancing
body transversely. The hurricane circle as it lies on the chart reveals
to him another important fact, which is, that if he pursue his course he
will sail _towards_ the axis line of the hurricane, and may stand a
chance of foundering in its centre. To avoid this he has one of two
courses to adopt; either to lay-to on the _starboard tack_, according to
Col. Reid's rules (see his 'Law of Storms,' 1st edit., pp. 425 to 428),
the ship being in the right-hand semicircle of the hurricane, or so to
alter his course as to keep without the influence of the storm. In the
present case the adoption of the latter alternative would involve a
reversal of his former course; nevertheless it is clear the more he
bears to the S.E. the less he will experience the violence of the
hurricane: should he heave his ship to, upon moving the hurricane circle
from the ship's place on the chart towards the N.E., he will be able to
judge of the changes of the wind he is likely to experience: thus it
will first veer to S.S.W., the barometer still falling; then to S.W.,
the barometer at a minimum--this marks the position of the most violent
portion of the storm he may be in, and by keeping the barometer as high
as he can by bearing towards the S.E., the farther he will be from the
centre--the barometer now begins to rise, the wind veering to W.S.W.,
and the hurricane finally passes off with the wind at W. It is to be
particularly remarked that in this example the ship is in the _most
dangerous quadrant_, as by scudding she would be driven in advance of
the track of the storm's centre, which of course would be approaching
her.
Assuming that the hurricane sets in at the ship's place with the wind at
S.E., the proceeding will be altogether different. At first the wind is
fair for the prosecution of the voyage, and it is desirable to take
advantage of this fair wind to avoid as much as possible the track of
the centre, which passes over the ship's place in this instance, and is
always the most dangerous part of the storm. As the ship is able to make
good distance from this track by bearing towards the N.W., provided she
has plenty of sea-room, she will experience less of the violence of the
hurricane; but as most of the Atlantic storms sweep over the shore, it
will be desirable to lay-to at some point on the _larboard tack_, the
ship being now in the left-hand semicircle. By moving the circle as
before directed it will be seen that the veering of the wind is now
E.S.E., E., E.N.E., N.E., the lowest barometer N.N.E., N., and N.N.W.,
the ship experiencing more or less of these changes as it is nearer to
or farther from the axis line.
In latitudes lower than 20° N. the Atlantic hurricanes usually move
towards the N.W. Taking the same positions of our ship with regard to
the storms as in the two former examples, if the storm set in with the
wind E. the proper proceeding is to bear away for the N.E., the most
dangerous quadrant of the hurricane having overtaken the ship, the
veering of the wind if she is lying-to will be E., E.S.E., S.E., with
the lowest barometer S.S.E. and S. Should the storm set in at N.E., her
position at the time will be some indication of the distance of the
centre's track from the nearest land, and will greatly assist in
determining the point at which the captain ought to lay-to after taking
advantage of the N.E. wind, should he be able so to do, to bear away
from the centre line, so as to avoid as much as possible the violence of
the storm. From the proximity of the West Indian Islands to this
locality of the storm-paths, the danger is proportionally increased.
The above examples have reference only to the lower and upper branches
of the storm paths of the Northern Atlantic in the neighbourhood of the
West Indies and the United States. In latitudes from about 25° to 32°
these paths usually _re-curve_, and at some point will move towards the
north. The veering of the wind will consequently be more or less
complicated according as the ship may be nearer to or farther from the
centre. The tables on page 11, combined with the first of those
immediately following the next paragraph, will, it is hoped, prove
advantageous in assisting the mariner as to the course to be adopted. As
a general principle we should say it would be best to bear to the
eastward, so as not only to avoid the greater fury of the storm, but to
get into the S. and S.W. winds, which give the principal chances of
making a westerly course.
We have in page 44 called attention to the fact that the storm paths
traced by Mr. Redfield do not extend eastward of the 50th meridian. This
by no means precludes the existence of severe storms and those of a
rotatory character in the great basin of the Northern Atlantic,
especially between the 40th and 50th parallels. A remarkable instance
has come under the author's attention of the wind hauling _apparently_
contrary to the usual theory: it may be that the storm route was in a
direction not generally observed. We are at the present moment destitute
of any information that at all indicates a _reversion_ of the rotation
in either hemisphere. The following tables constructed for the northern
hemisphere, and for storm routes _not yet ascertained_, may probably be
consulted with advantage on anomalous occasions.
HURRICANE MOVING FROM SOUTH TO NORTH.
Axis line, wind E., barometer falling, first half of storm.
Axis line, wind W., barometer rising, last half of storm.
RIGHT-HAND SEMICIRCLE.
Wind E.S.E., S.E., S.S.E., S., barometer falling, first half of storm.
Wind W.S.W., S.W., S.S.W., S., barometer rising, last half of storm.
LEFT-HAND SEMICIRCLE.
Wind E.N.E., N.E., N.N.E., N., barometer falling, first half of storm.
Wind W.N.W., N.W., N.N.W., N., barometer rising, last half of storm.
HURRICANE MOVING FROM NORTH TO SOUTH.
Axis line, wind W., barometer falling, first half of storm.
Axis line, wind E., barometer rising, last half of storm.
RIGHT-HAND SEMICIRCLE.
Wind W.N.W., N.W., N.N.W., N., barometer falling, first half of storm.
Wind E.N.E., N.E., N.N.E., N., barometer rising, last half of storm.
LEFT-HAND SEMICIRCLE.
Wind W.S.W., S.W., S.S.W., S., barometer falling, first half of storm.
Wind E.S.E., S.E., S.S.E., S,, barometer rising, last half of storm.
HURRICANE MOVING PROM WEST TO EAST.
Axis line, wind S., barometer falling, first half of storm.
Axis line, wind N., barometer rising, last half of storm.
RIGHT-HAND SEMICIRCLE.
Wind S.S.W., S.W., W.S.W., W., barometer falling, first half of storm.
Wind N.N.W., N.W., W.N.W., W., barometer rising, last half of storm.
LEFT-HAND SEMICIRCLE.
Wind S.S.E., S.E., E.S.E., E., barometer falling, first half of storm.
Wind N.N.E., N.E., E.N.E., E., barometer rising, last half of storm.
HURRICANE MOVING FROM NORTH-WEST TO SOUTH-EAST.
Axis line, wind S.W., barometer falling, first half of storm.
Axis line, wind N.E., barometer rising, last half of storm.
RIGHT-HAND SEMICIRCLE.
Wind W.S.W., W., W.N.W., N.W., barometer falling, first half of storm.
Wind N.N.E., N., N.N.W., N.W., barometer rising, last half of storm.
LEFT-HAND SEMICIRCLE.
Wind S.S.W., S., S.S.E., S.E., barometer falling, first half of storm.
Wind E.N.E., E., E.S.E., S.E., barometer rising, last half of storm.
APPENDIX.
TABLE I.--Correction to be added to Barometers for Capillary Action.
+--------------------+---------------------------------+
| | Correction for |
| Diameter of Tube. |-----------------+---------------|
| | Unboiled Tubes. | Boiled Tubes. |
|--------------------|-----------------|---------------|
| Inch. | Inch. | Inch. |
| 0·60 | 0·004 | 0·002 |
| 0·50 | 0·007 | 0·003 |
| 0·45 | 0·010 | 0·005 |
| 0·40 | 0·014 | 0·007 |
| 0·35 | 0·020 | 0·010 |
| 0·30 | 0·028 | 0·014 |
| 0·25 | 0·040 | 0·020 |
| 0·20 | 0·060 | 0·029 |
| 0·15 | 0·088 | 0·044 |
| 0·10 | 0·142 | 0·070 |
+--------------------+-----------------+---------------+
+---------------------------------------------------------------------+
|Transcibers note: The following 100 line table has been split into |
|two, both vertically and horizontally, so that it can be accommodated|
|on these pages. |
+---------------------------------------------------------------------+
TABLE II.--Correction to be applied to Barometers with _Brass Scales_,
extending from the Cistern to the top of the Mercurial Column, to reduce
the observation to 32° Fahrenheit.
---+------------------------------------------------------------+----
| I N C H E S. |
T | -----+-------+------+-------+------+-------+------+--------| T
e | | | | | | | | | e
m | 24 | 24·5 | 25 | 25·5 | 26 | 26·5 | 27 | 27·5 | m
p | | | | | | | | | p
---+------+-------+------+-------+------+-------+------+--------+----
° | + | + | + | + | + | + | + | + | °
0 | ·061 | ·063 | ·064 | ·065 | ·067 | ·068 | ·069 | ·071 | 0
1 | ·059 | ·061 | ·062 | ·063 | ·064 | ·065 | ·067 | ·068 | 1
2 | ·057 | ·058 | ·060 | ·061 | ·062 | ·063 | ·064 | ·066 | 2
3 | ·055 | ·056 | ·057 | ·059 | ·060 | ·061 | ·062 | ·063 | 3
4 | ·053 | ·054 | ·055 | ·056 | ·057 | ·058 | ·059 | ·061 | 4
5 | ·051 | ·052 | ·053 | ·054 | ·055 | ·056 | ·057 | ·058 | 5
6 | ·049 | ·050 | ·051 | ·052 | ·053 | ·054 | ·055 | ·056 | 6
7 | ·046 | ·047 | ·048 | ·049 | ·050 | ·051 | ·052 | ·053 | 7
8 | ·044 | ·045 | ·046 | ·047 | ·048 | ·049 | ·050 | ·051 | 8
9 | ·042 | ·043 | ·044 | ·045 | ·046 | ·046 | ·047 | ·048 | 9
10 | ·040 | ·041 | ·042 | ·042 | ·043 | ·044 | ·045 | ·046 | 10
| | | | | | | | |
11 | ·038 | ·039 | ·039 | ·040 | ·041 | ·042 | ·042 | ·043 | 11
12 | ·036 | ·036 | ·037 | ·038 | ·039 | ·039 | ·040 | ·041 | 12
13 | ·033 | ·034 | ·035 | ·036 | ·036 | ·037 | ·038 | ·038 | 13
14 | ·031 | ·032 | ·033 | ·033 | ·034 | ·035 | ·035 | ·036 | 14
15 | ·029 | ·030 | ·030 | ·031 | ·032 | ·032 | ·033 | ·033 | 15
16 | ·027 | ·028 | ·028 | ·029 | ·029 | ·030 | ·030 | ·031 | 16
17 | ·025 | ·025 | ·026 | ·026 | ·027 | ·027 | ·028 | ·028 | 17
18 | ·023 | ·023 | ·024 | ·024 | ·025 | ·025 | ·025 | ·026 | 18
19 | ·021 | ·021 | ·021 | ·022 | ·022 | ·023 | ·023 | ·024 | 19
20 | ·018 | ·019 | ·019 | ·020 | ·020 | ·020 | ·021 | ·021 | 20
| | | | | | | | |
21 | ·016 | ·017 | ·017 | ·017 | ·018 | ·018 | ·018 | ·019 | 21
22 | ·014 | ·014 | ·015 | ·015 | ·015 | ·016 | ·016 | ·016 | 22
23 | ·012 | ·012 | ·012 | ·013 | ·013 | ·013 | ·013 | ·014 | 23
24 | ·010 | ·010 | ·010 | ·010 | ·011 | ·011 | ·011 | ·011 | 24
25 | ·008 | ·008 | ·008 | ·008 | ·008 | ·008 | ·009 | ·009 | 25
26 | ·005 | ·006 | ·006 | ·006 | ·006 | ·006 | ·006 | ·006 | 26
27 | ·003 | ·003 | ·003 | ·003 | ·004 | ·004 | ·004 | ·004 | 27
28 | ·001 | ·001 | ·001 | ·001 | ·001 | ·001 | ·001 | ·001 | 28
| -- | -- | -- | -- | -- | -- | -- | -- |
29 | ·001 | ·001 | ·001 | ·001 | ·001 | ·001 | ·001 | ·001 | 29
30 | ·003 | ·003 | ·003 | ·004 | ·004 | ·004 | ·004 | ·004 | 30
| | | | | | | | |
31 | ·005 | ·006 | ·006 | ·006 | ·006 | ·006 | ·006 | ·006 | 31
32 | ·008 | ·008 | ·008 | ·008 | ·008 | ·008 | ·008 | ·009 | 32
33 | ·010 | ·010 | ·010 | ·010 | ·011 | ·011 | ·011 | ·011 | 33
34 | ·012 | ·012 | ·012 | ·013 | ·013 | ·013 | ·013 | ·014 | 34
35 | ·014 | ·014 | ·015 | ·015 | ·015 | ·015 | ·016 | ·016 | 35
36 | ·016 | ·017 | ·017 | ·017 | ·017 | ·018 | ·018 | ·019 | 36
37 | ·018 | ·019 | ·019 | ·019 | ·020 | ·020 | ·021 | ·021 | 37
38 | ·020 | ·021 | ·021 | ·022 | ·022 | ·023 | ·023 | ·023 | 38
39 | ·023 | ·023 | ·024 | ·024 | ·024 | ·025 | ·025 | ·026 | 39
40 | ·025 | ·025 | ·026 | ·026 | ·027 | ·027 | ·028 | ·028 | 40
| | | | | | | | |
41 | ·027 | ·027 | ·028 | ·029 | ·029 | ·030 | ·030 | ·031 | 41
42 | ·029 | ·030 | ·030 | ·031 | ·031 | ·032 | ·033 | ·033 | 42
43 | ·031 | ·032 | ·032 | ·033 | ·034 | ·034 | ·035 | ·036 | 43
44 | ·033 | ·034 | ·035 | ·035 | ·036 | ·037 | ·037 | ·038 | 44
45 | ·035 | ·036 | ·037 | ·038 | ·038 | ·039 | ·040 | ·041 | 45
46 | ·038 | ·038 | ·039 | ·040 | ·041 | ·042 | ·042 | ·043 | 46
47 | ·040 | ·041 | ·041 | ·042 | ·043 | ·044 | ·045 | ·046 | 47
48 | ·042 | ·043 | ·044 | ·045 | ·045 | ·046 | ·047 | ·048 | 48
49 | ·044 | ·045 | ·046 | ·047 | ·043 | ·049 | ·050 | ·050 | 49
50 | ·046 | ·047 | ·043 | ·049 | ·050 | ·051 | ·052 | ·053 | 50
---+------+-------+------+-------+------+-------+------+--------+----
---+-----------------------------------------------------+----
| I N C H E S. |
T |-------+------+-------+------+-------+------+--------| T
e | | | | | | | | e
m | 28 | 28·5 | 29 | 29·5 | 30 | 30·5 | 31 | m
p | | | | | | | | p
---+-------+------+-------+------+-------+------+--------+----
° | + | + | + | + | + | + | + | °
0 | ·072 | ·073 | ·074 | ·076 | ·077 | ·078 | ·080 | 0
1 | ·069 | ·071 | ·072 | ·073 | ·074 | ·076 | ·077 | 1
2 | ·067 | ·068 | ·069 | ·070 | ·072 | ·073 | ·074 | 2
3 | ·064 | ·065 | ·067 | ·068 | ·069 | ·070 | ·071 | 3
4 | ·062 | ·063 | ·064 | ·065 | ·066 | ·067 | ·068 | 4
5 | ·039 | ·060 | ·061 | ·062 | ·063 | ·065 | ·066 | 5
6 | ·057 | ·058 | ·059 | ·060 | ·061 | ·062 | ·063 | 6
7 | ·054 | ·055 | ·056 | ·057 | ·058 | ·059 | ·060 | 7
8 | ·052 | ·053 | ·054 | ·054 | ·055 | ·056 | ·057 | 8
9 | ·049 | ·050 | ·051 | ·052 | ·053 | ·054 | ·054 | 9
10 | ·047 | ·047 | ·048 | ·049 | ·050 | ·051 | ·052 | 10
| | | | | | | |
11 | ·044 | ·045 | ·046 | ·046 | ·047 | ·048 | ·049 | 11
12 | ·042 | ·042 | ·043 | ·044 | ·045 | ·045 | ·046 | 12
13 | ·039 | ·040 | ·040 | ·041 | ·042 | ·043 | ·043 | 13
14 | ·037 | ·037 | ·038 | ·038 | ·039 | ·040 | ·040 | 14
15 | ·034 | ·035 | ·035 | ·036 | ·036 | ·037 | ·038 | 15
16 | ·032 | ·032 | ·033 | ·033 | ·034 | ·034 | ·035 | 16
17 | ·029 | ·030 | ·030 | ·031 | ·031 | ·032 | ·032 | 17
18 | ·026 | ·027 | ·027 | ·028 | ·028 | ·029 | ·029 | 18
19 | ·024 | ·024 | ·025 | ·025 | ·026 | ·026 | ·027 | 19
20 | ·021 | ·022 | ·022 | ·023 | ·023 | ·023 | ·024 | 20
| | | | | | | |
21 | ·019 | ·019 | ·020 | ·020 | ·020 | ·021 | ·021 | 21
22 | ·016 | ·017 | ·017 | ·017 | ·018 | ·018 | ·018 | 22
23 | ·014 | ·014 | ·014 | ·015 | ·015 | ·015 | ·015 | 23
24 | ·011 | ·012 | ·012 | ·012 | ·012 | ·012 | ·013 | 24
25 | ·009 | ·009 | ·009 | ·009 | ·009 | ·010 | ·010 | 25
26 | ·006 | ·006 | ·007 | ·007 | ·007 | ·007 | ·007 | 26
27 | ·004 | ·004 | ·004 | ·004 | ·004 | ·004 | ·004 | 27
28 | ·001 | ·001 | ·001 | ·001 | ·001 | ·001 | ·001 | 28
| -- | -- | -- | -- | -- | -- | -- |
29 | ·001 | ·001 | ·001 | ·001 | ·001 | ·001 | ·001 | 29
30 | ·004 | ·004 | ·004 | ·004 | ·004 | ·004 | ·004 | 30
| | | | | | | |
31 | ·006 | ·006 | ·007 | ·007 | ·007 | ·007 | ·007 | 31
32 | ·009 | ·009 | ·009 | ·009 | ·009 | ·010 | ·010 | 32
33 | ·011 | ·012 | ·012 | ·012 | ·012 | ·012 | ·012 | 33
34 | ·014 | ·014 | ·014 | ·015 | ·015 | ·015 | ·015 | 34
35 | ·016 | ·017 | ·017 | ·017 | ·018 | ·018 | ·018 | 35
36 | ·019 | ·019 | ·020 | ·020 | ·020 | ·021 | ·021 | 36
37 | ·021 | ·022 | ·022 | ·022 | ·023 | ·023 | ·024 | 37
38 | ·024 | ·024 | ·025 | ·025 | ·026 | ·026 | ·026 | 38
39 | ·026 | ·027 | ·027 | ·028 | ·028 | ·029 | ·029 | 39
40 | ·029 | ·029 | ·030 | ·030 | ·031 | ·031 | ·032 | 40
| | | | | | | |
41 | ·031 | ·032 | ·033 | ·033 | ·034 | ·034 | ·035 | 41
42 | ·034 | ·034 | ·035 | ·036 | ·036 | ·037 | ·037 | 42
43 | ·036 | ·037 | ·038 | ·038 | ·039 | ·010 | ·040 | 43
44 | ·039 | ·040 | ·040 | ·041 | ·042 | ·042 | ·043 | 44
45 | ·041 | ·042 | ·043 | ·044 | ·044 | ·045 | ·046 | 45
46 | ·044 | ·045 | ·045 | ·046 | ·047 | ·048 | ·049 | 46
47 | ·046 | ·047 | ·048 | ·049 | ·050 | ·051 | ·051 | 47
48 | ·049 | ·050 | ·051 | ·052 | ·052 | ·053 | ·054 | 48
49 | ·031 | ·052 | ·053 | ·054 | ·055 | ·056 | ·057 | 49
50 | ·054 | ·055 | ·056 | ·057 | ·058 | ·059 | ·060 | 50
---+-------+------+-------+------+-------+------+--------+----
TABLE II.--_Continued_
----+------------------------------------------------------------+-----
| I N C H E S. |
T |------+-------+------+-------+------+-------+------+--------| T
e | | | | | | | | | e
m | 24 | 24·5 | 25 | 25·5 | 26 | 26·5 | 27 | 27·5 | m
p | | | | | | | | | p
----+------+-------+------+-------+------+-------+------+--------+-----
° | + | + | + | + | + | + | + | + | °
51 | ·048 | ·049 | ·050 | ·051 | ·052 | ·053 | ·054 | ·055 | 51
52 | ·050 | ·052 | ·053 | ·054 | ·055 | ·056 | ·057 | ·058 | 52
53 | ·053 | ·054 | ·055 | ·056 | ·057 | ·058 | ·059 | ·060 | 53
54 | ·055 | ·056 | ·057 | ·053 | ·059 | ·060 | ·062 | ·063 | 54
55 | ·057 | ·058 | ·059 | ·060 | ·062 | ·063 | ·064 | ·065 | 55
56 | ·059 | ·060 | ·061 | ·063 | ·064 | ·065 | ·066 | ·063 | 56
57 | ·061 | ·062 | ·064 | ·065 | ·066 | ·068 | ·069 | ·070 | 57
58 | ·063 | ·065 | ·066 | ·067 | ·069 | ·070 | ·071 | ·073 | 58
59 | ·065 | ·067 | ·068 | ·070 | ·071 | ·072 | ·074 | ·075 | 59
60 | ·068 | ·069 | ·070 | ·072 | ·073 | ·075 | ·076 | ·077 | 60
| | | | | | | | |
61 | ·070 | ·071 | ·073 | ·074 | ·075 | ·077 | ·078 | ·080 | 61
62 | ·072 | ·073 | ·075 | ·076 | ·078 | ·079 | ·081 | ·082 | 62
63 | ·074 | ·076 | ·077 | ·079 | ·080 | ·082 | ·083 | ·085 | 63
64 | ·076 | ·073 | ·079 | ·081 | ·082 | ·084 | ·086 | ·087 | 64
65 | ·078 | ·080 | ·082 | ·083 | ·085 | ·086 | ·088 | ·090 | 65
66 | ·080 | ·082 | ·084 | ·085 | ·087 | ·089 | ·090 | ·092 | 66
67 | ·083 | ·084 | ·086 | ·088 | ·089 | ·091 | ·093 | ·095 | 67
68 | ·085 | ·086 | ·088 | ·090 | ·092 | ·094 | ·095 | ·097 | 68
69 | ·087 | ·089 | ·090 | ·092 | ·094 | ·096 | ·098 | ·100 | 69
70 | ·089 | ·091 | ·093 | ·095 | ·096 | ·098 | ·100 | ·102 | 70
| | | | | | | | |
71 | ·091 | ·093 | ·095 | ·097 | ·099 | ·101 | ·102 | ·104 | 71
72 | ·093 | ·095 | ·097 | ·099 | ·101 | ·103 | ·105 | ·107 | 72
73 | ·095 | ·097 | ·099 | ·101 | ·103 | ·105 | ·107 | ·109 | 73
74 | ·097 | ·099 | ·102 | ·104 | ·106 | ·108 | ·110 | ·112 | 74
75 | ·100 | ·102 | ·104 | ·106 | ·108 | ·110 | ·112 | ·114 | 75
76 | ·102 | ·104 | ·106 | ·108 | ·110 | ·112 | ·114 | ·117 | 76
77 | ·104 | ·106 | ·108 | ·110 | ·112 | ·115 | ·117 | ·119 | 77
78 | ·106 | ·108 | ·110 | ·113 | ·115 | ·117 | ·119 | ·122 | 78
79 | ·108 | ·110 | ·113 | ·115 | ·117 | ·119 | ·122 | ·124 | 79
80 | ·110 | ·113 | ·115 | ·117 | ·119 | ·122 | ·124 | ·126 | 80
| | | | | | | | |
81 | ·112 | ·115 | ·117 | ·119 | ·122 | ·124 | ·126 | ·129 | 81
82 | ·114 | ·117 | ·119 | ·122 | ·124 | ·126 | ·129 | ·131 | 82
83 | ·117 | ·119 | ·121 | ·124 | ·126 | ·129 | ·131 | ·134 | 83
84 | ·119 | ·121 | ·124 | ·126 | ·129 | ·131 | ·134 | ·136 | 84
85 | ·121 | ·123 | ·136 | ·128 | ·131 | ·133 | ·136 | ·139 | 85
86 | ·123 | ·126 | ·128 | ·131 | ·133 | ·136 | ·138 | ·141 | 86
87 | ·125 | ·128 | ·130 | ·133 | ·136 | ·138 | ·141 | ·143 | 87
88 | ·127 | ·130 | ·133 | ·133 | ·138 | ·141 | ·143 | ·146 | 88
89 | ·129 | ·132 | ·135 | ·137 | ·140 | ·143 | ·146 | ·148 | 89
90 | ·131 | ·134 | ·137 | ·140 | ·142 | ·145 | ·148 | ·151 | 90
| | | | | | | | |
91 | ·134 | ·136 | ·139 | ·142 | ·145 | ·148 | ·150 | ·153 | 91
92 | ·136 | ·139 | ·141 | ·144 | ·147 | ·150 | ·153 | ·156 | 92
93 | ·138 | ·141 | ·144 | ·147 | ·149 | ·152 | ·155 | ·158 | 93
94 | ·140 | ·143 | ·146 | ·149 | ·152 | ·155 | ·157 | ·161 | 94
95 | ·142 | ·145 | ·148 | ·151 | ·154 | ·157 | ·160 | ·163 | 95
96 | ·144 | ·147 | ·150 | ·153 | ·156 | ·159 | ·162 | ·165 | 96
97 | ·146 | ·149 | ·152 | ·155 | ·159 | ·162 | ·165 | ·168 | 97
98 | ·148 | ·152 | ·155 | ·158 | ·161 | ·164 | ·167 | ·170 | 98
99 | ·151 | ·154 | ·157 | ·160 | ·163 | ·166 | ·169 | ·173 | 99
100 | ·153 | ·156 | ·159 | ·162 | ·165 | ·169 | ·172 | ·175 | 100
----+------+-------+------+-------+------+-------+------+--------+-----
----+-----------------------------------------------------+-----
| I N C H E S. |
T |-------+------+-------+------+-------+------+--------| T
e | | | | | | | | e
m | 28 | 28·5 | 29 | 29·5 | 30 | 30·5 | 31 | m
p | | | | | | | | p
----+-------+------+-------+------+-------+------+--------+-----
° | + | + | + | + | + | + | + | °
51 | ·056 | ·057 | ·058 | ·059 | ·060 | ·061 | ·062 | 51
52 | ·059 | ·060 | ·061 | ·062 | ·063 | ·064 | ·065 | 52
53 | ·061 | ·063 | ·064 | ·065 | ·066 | ·067 | ·068 | 53
54 | ·064 | ·065 | ·066 | ·067 | ·068 | ·070 | ·071 | 54
55 | ·066 | ·068 | ·069 | ·070 | ·071 | ·072 | ·073 | 55
56 | ·069 | ·070 | ·071 | ·073 | ·074 | ·075 | ·076 | 56
57 | ·071 | ·073 | ·074 | ·075 | ·076 | ·078 | ·079 | 57
58 | ·074 | ·075 | ·077 | ·078 | ·079 | ·081 | ·082 | 58
59 | ·076 | ·078 | ·079 | ·080 | ·082 | ·083 | ·085 | 59
60 | ·079 | ·080 | ·082 | ·083 | ·085 | ·086 | ·087 | 60
| | | | | | | |
61 | ·081 | ·083 | ·084 | ·086 | ·087 | ·089 | ·090 | 61
62 | ·084 | ·085 | ·087 | ·088 | ·090 | ·091 | ·093 | 62
63 | ·086 | ·088 | ·089 | ·091 | ·093 | ·094 | ·096 | 63
64 | ·089 | ·090 | ·092 | ·094 | ·095 | ·097 | ·098 | 64
65 | ·091 | ·093 | ·095 | ·096 | ·098 | ·100 | ·101 | 65
66 | ·094 | ·096 | ·097 | ·099 | ·101 | ·102 | ·104 | 66
67 | ·096 | ·098 | ·100 | ·102 | ·103 | ·105 | ·107 | 67
68 | ·099 | ·101 | ·102 | ·104 | ·106 | ·108 | ·109 | 68
69 | ·101 | ·103 | ·105 | ·107 | ·109 | ·110 | ·112 | 69
70 | ·104 | ·106 | ·108 | ·109 | ·111 | ·113 | ·115 | 70
| | | | | | | |
71 | ·106 | ·108 | ·110 | ·112 | ·114 | ·116 | ·118 | 71
72 | ·109 | ·111 | ·113 | ·115 | ·117 | ·119 | ·120 | 72
73 | ·111 | ·113 | ·115 | ·117 | ·119 | ·121 | ·123 | 73
74 | ·114 | ·116 | ·118 | ·120 | ·122 | ·124 | ·126 | 74
75 | ·116 | ·118 | ·120 | ·122 | ·125 | ·127 | ·129 | 75
76 | ·119 | ·121 | ·123 | ·125 | ·127 | ·129 | ·131 | 76
77 | ·121 | ·123 | ·126 | ·128 | ·130 | ·132 | ·134 | 77
78 | ·124 | ·126 | ·128 | ·130 | ·133 | ·135 | ·137 | 78
79 | ·126 | ·128 | ·131 | ·133 | ·135 | ·137 | ·140 | 79
80 | ·129 | ·131 | ·133 | ·136 | ·138 | ·140 | ·143 | 80
| | | | | | | |
81 | ·131 | ·134 | ·136 | ·138 | ·141 | ·143 | ·145 | 81
82 | ·134 | ·136 | ·138 | ·141 | ·143 | ·146 | ·148 | 82
83 | ·136 | ·139 | ·141 | ·143 | ·146 | ·148 | ·151 | 83
84 | ·139 | ·141 | ·144 | ·146 | ·149 | ·151 | ·154 | 84
85 | ·141 | ·144 | ·146 | ·149 | ·151 | ·154 | ·156 | 85
86 | ·144 | ·146 | ·149 | ·151 | ·154 | ·156 | ·159 | 86
87 | ·146 | ·149 | ·151 | ·154 | ·157 | ·159 | ·162 | 87
88 | ·149 | ·151 | ·154 | ·157 | ·159 | ·162 | ·165 | 88
89 | ·151 | ·154 | ·156 | ·159 | ·162 | ·165 | ·167 | 89
90 | ·153 | ·156 | ·159 | ·162 | ·164 | ·167 | ·170 | 90
| | | | | | | |
91 | ·156 | ·159 | ·162 | ·165 | ·167 | ·170 | ·173 | 91
92 | ·158 | ·161 | ·164 | ·167 | ·170 | ·172 | ·175 | 92
93 | ·161 | ·164 | ·167 | ·170 | ·172 | ·175 | ·178 | 93
94 | ·163 | ·166 | ·169 | ·172 | ·175 | ·177 | ·180 | 94
95 | ·166 | ·169 | ·172 | ·175 | ·178 | ·180 | ·183 | 95
96 | ·168 | ·171 | ·174 | ·178 | ·181 | ·183 | ·116 | 96
97 | ·171 | ·174 | ·177 | ·180 | ·183 | ·186 | ·189 | 97
98 | ·173 | ·176 | ·179 | ·183 | ·186 | ·188 | ·191 | 98
99 | ·176 | ·179 | ·182 | ·185 | ·188 | ·191 | ·194 | 99
100 | ·178 | ·181 | ·184 | ·188 | ·191 | ·194 | ·197 | 100
----+-------+------+-------+------+-------+------+--------+-----
PRINTED BY W. CLOWES AND SONS, STANFORD STREET. FOOTNOTES:
[1] The first half of the storm, _in the case before alluded to_, is
that N.E. of the line N.W.--S.E., fig. 1, comprising the easterly and
southerly winds; and the latter half, that S.W. of the same line,
comprising the northerly and westerly winds.
[2] This table is also applicable to the hurricanes in the neighbourhood
of Mauritius in the southern hemisphere, where all the phænomena are
reversed; the motion of the hurricanes being towards the S.W., and the
rotation in the direction of the hands of a watch, the same barometric
and anemonal phænomena are experienced as in a hurricane in the northern
hemisphere moving towards the N.E.
[3] By the officer of the watch being charged with this duty, and its
being executed under his immediate superintendence, it is apprehended
that a register may be kept with great regularity.
[4] These papers may be obtained from Messrs. W. H. Allen and Co.,
Booksellers to the Honourable East India Company, No. 7, Leadenhall
Street, London.
[5] Reports of the British Association for the Advancement of Science,
1846, p. 139.
End of Project Gutenberg's The Hurricane Guide, by William Radcliff Birt