Correction for Temperature.—The barometer is always registered as if the temperature of the mercury were 32° Fahr. If the temperature of the mercury be above this, the metal expands, and reads higher than it would do at 32°. The amount of expansion of mercury is 0001001 of its bulk for each degree; but the linear expansion of the brass scale must also be considered. Schumacher's formula is used for the correction, viz.—

A observed height of barometer in inches. t-temperature of attached thermometer (Fahr.) m=expansion of mercury per degree, viz, 0001001. 1-linear expansion of scale, viz., 000104344; normal temperature being 62°.

Sir H. James' work, which is distributed to army medical officers, contains tables which greatly facilitate the correction for temperature. The one which we give here will doubtless be found of use.

Correction for Sea-Level.-As the mercury falls about Too (001 inch) for every foot of ascent, this amount multiplied by the number of feet must be added to the height, if the place be above sea-level. The temperature of the air has also to be taken into account if great accuracy is required.

TABLE I.-FOR REDUCTION OF BAROMETER TO FREEZING-POINT.

The number opposite the temperature of attached thermometer is to be deducted.

ascended to cause the observed fall, and then making a correction for temperature by multiplying the number obtained from the table, which may be called A, by the formula-t is the temperature of the lower and t' of the upper station)—

Measurement of Heights.-When heights | the number of feet which must have been are ascended a certain amount of air is left below, so the barometer falls. The diminution is not uniform, for the higher the ascent the less weighty the air; and a greater and greater height must be ascended to depress the barometer one inch. This is illustrated by the following table (the height can be readily taken from this table by calculating

1+

t+t' - 64
$900

+ A

The measurements of heights in this way is of great use to medical officers; the aneroid barometer can be used as high as 5000 feet, and a delicate instrument will measure as little as 4 feet. A great many plans are in use for calculating heights; it can easily be done by logarithms, but it is not always that it is convenient to obtain a table of logarithms. The simplest rule of all is one derived from Laplace's formula. In the Proceedings of the Royal Society, 1865, No. 75, p. 283, Mr. Ellis has lately stated this formula as follows: Multiply the difference of the barometric readings by 52,400, and divide by the sum of the barometric readings. If the result be 1000, 2000, 3000, 4000, or 5000, add 0, 0, 2, 6, | 14 respectively. Subtract 2 times the difference of the temperature of the mercury. Multiply the remainder by a number obtained by adding 836 to the sum of the temperatures of the air, and dividing by 900. A correction must also be given for latitude, which can be done by Table IV., p. 80.

If the height is less than 300 feet, Tables III.,
IV., V., need not be used.

=

TABLE II. is calculated from the formula, height in feet 60,200 (log. 29 922 log. B)+ 952; where 29-922 is the mean atmospheric pressure at 32° Fahr. and the mean sea-level in latitude 45°, and B is any other barometric pressure, the 952 being added to avoid minus signs in the table.

TABLE III. contains the correction necessary for the mean temperature of the stratum of air between the stations of observation, and is computed from Regnault's coefficient for the expansion of air, which is '002036 of its volume at 32° for each degree above that temperature.

TABLE IV. is the correction due to the difference of gravitation in any other latitude, and is found from the formula x = 1 + 00265 cos. 2 lat.

==

TABLE V. is to correct for the diminution of gravity in ascending from the sea-level.

Negretti and Zambra say: "To use these tables, the barometer readings at the upper and lower stations having been corrected and reduced to temperature 32° Fahr., take out from Table I. the numbers opposite the corrected readings of the two barometers, and subtract the lower from the upper. Multiply this difference successively by the factors found in Tables III. and IV. The factor from Table IV. may be neglected unless precision is desired. Finally, add the correction taken from Table V."

In the table the barometer is only read to 10ths, but it should be read to 100ths ('01) and 1000ths (001), and the number of feet corresponding to these amounts calculated from the tables.*

Messrs. Negretti and Zambra, in their "Treatise on Meteorological Instruments" (1864), give tables for estimating the approximate height due to barometric pressure, and these are the easiest formula we know of. We give them here. (Tables II., III., IV., and V.) A good mercurial barometer with an attached thermometer, or an aneroid compensated for temperature, and a thermometer to ascertain the temperature of the air, are required. Two barometers and two thermometers, which can be observed at the same moment at the upper and lower stations, are desirable. Supposing, however, there is but one barometer, take the height at the lower station and correct for temperature to 32°, according to the table for reduction of barometer to freezing-point, p. 77. Take the temperature of the air. Ascend as rapidly as possible to the upper Latitude, 51°-Factor from Table IV. station, and take the height of the barometer (correcting it to 32°) and the temperature of the air; then use Tables II., III., IV., and V.

* Example.-On the 21st October 1852, when Mr. Welsh ascended in a balloon at 3h. 30m. P. M., the

barometer, corrected and reduced, was 18 85, the air temperature 27; while at Greenwich, 159 feet above the sea, the barometer at the same time was 29 97 inches, air temperature 49°, the balloon not being more than five miles S. W. from over Greenwich; required its elevation.

* There is, however, a convenient little book by Sang of logarithms to five places, which will go in the waistcoat-pocket.

"

Fect.

Barometer in balloon, 18-85, Table II. 18,007 at Greenwich, 29.97, 883 12,124

Mean temperature, 38-Table III. Factor.

Correction from Table V.

.

Elevation of Greenwich

1,012

12.269

99,941

12,262

38

12,300

159

TABLE II.-APPROXIMATE HEIGHT DUE TO BAROMETRIC PRESSURE.

TABLE III.-CORRECTION DUE TO MEAN TEMPERATURE OF AIR:

The temperature of the upper and lower station being added and divided by 2.

TABLE IV.-CORRECTION DUE TO DIFFERENCE OF GRAVITATION IN DIFFERENT LATITUDES.

TABLE VI.-SHOWING THE WEIGHT IN GRAINS OF A CUBIC FOOT OF DRY AIR under pressure of 30 inches of Mercury for every degree from 0 to 100.

Barracks-The parts of a barrack consist of-1. The barrack-room, and non-commissioned officers' (sergeants, &c.) room screened off; 2. quarters of the married privates; 3. quarters of the staff-sergeant and sergeants' mess; 4. quarters of the officers; 5. kitchens;

Then the height of the higher station above 6. ablution rooms; 7. latrines and urinals; the lower in feet

8. orderly room and guard-room; 9. cells; 10. tailors' shop and armoury commissariat stores, canteen; 11. reading-room (in many barracks), schools, magazine.

The hygiène of barracks is evidently sub

For rapid calculation, the following, though ject to the same principles as habitations (see less exact, is convenient :-

Height in feet 56300 (log. H

t

(1+) nearly.

900

HABITATIONS), yet there are some special log. h). points which require notice.

About fifteen years ago the barracks of this country were so ill-constructed, so confined

In the absence of logarithms, the following as to cubic space, and therefore so impure as

F