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

hould 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.


_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


_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



Corr. for temperature - ·068



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 ______.



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."