CATALOGUE. — METEOROLOGY, BAROMETRICAL MEASUREMENTS. 4?S

Barometrical experiments give and T! ' r The specificgravity of mercury at 68° is 13.61. The decrease of gravityin ascending from the earth's surface produces no percepti-ble effect. Logarithms give fathoms at 31 . 24 “.*Shuckburgb’s comparison of his rules withGeneral Roy’s. Ph. tr. 1778. 681.

Thinks, that either Roy’s rules or his own are sufficientlyaccurate.

•Roy on the measurement of heights. Ph.tr. 1777. 653.

Finds, that logarithms give fathoms about 31.7° in Eng-land, but at Spitzbergen about 61°, and at the equator near0° : the difference may perhaps depend on moisture : thesame cause appears to require a correction for the meanheight above the sea, of which a table is given, the cor-rection for temperature being diminished about for eachinch that the mean height of the barometer is below 30°.After all possible corrections, the height of Moel Eilio camenut near r > 5 too great: if Dcluc’s rules had been employed,the error would have been greater.

Cliiminello on barometrical measurements.Iloz. XI [I. 457.

pouchy on the weight of the air. A. P. 1780.

3.

Magellan ’s description of barometers.Magellan ’s barometer. Roz. XIX. 108,194,257,341.

Acluird on measuring heights by boilingwater. A. Bed. 1782. 54. Roz. XXV. 287.Damen de moniium altitudine. Hague, 1783.Pasuinot. Roz. XXIX. 13.

Trembley in Saussurc Voyages. III.Trembley’s remarks on Deluc. Roz. XXXII.87. XLII. 181.

Mayer liber das bdbenmessen 8. Frankf.1787-

Mayer iiberdie war me in iiicksicht auf dembarometer. 8. Frankf. 1796.

* Playfair. Ed. tr. I. 87.

Accurate calculations.

Saussure on the density of the air at differentheights. Roz. XXXVI. 98.

Morozzo on die constitution of the air. Soc.

Ital. VI. 221.

VOL. II.

Gerstner and Gruber on the density of the.

air. Roz. Xld. 110.

Robison. Enc. Br. Art. Pneumatics.Hamilton. Ir. tr. V. 117.

Wild on the influence of the wind. Zach.Eph. IV. 385.

Laplace Exposition du systeme du inonde.

follows Deluc.

Laplace Meeanique cdleste. IV.

Rhode liber die berechnung der bcrgliohennaeh Laplace. Halle, 1803.

Berger’s mode of bringing down air in hot-ties. Journ. Phys. LVI. 366.

Lambert gives It =10 oool. —— --- J ' for the

y 31-583—y

height in toisei, y being the height of the mercury in inchesFr.

Deluc's rule is h — 10 000 1.

y \ 484 /

484

toiscs, /being the degrees of Fahrenheit.

Maskclync’s ruh: deduced from Deluc’s is h iz (10 000 1.

(?) + . 452 g ^ g being the difference of

the temperatures. Or, if we use a thermometer on whichthe freezing point is at o° and the boiling point at 81 . 4 °,for measuring the temperature of the mercury, and anotherwith the freezing point at — 0 °,and the boiling point at tai*

for that of the air, we shall have h — (10000 1. <?*>

( i 4- f-iiV f being the difference of the mercurial tem-1000 /

peratures, and k and / the temperatures of the air.

Shuckburgh says, that for common practice, when theheight is less than a mile, it is sufficient to allow 01-72 feetfor every tenth of an inch of difference, adding .211 f. foreach degree above 55°, and increasing the whole in tile ra-tio of 30 inches to the mean height of the barometers. Oneten thousandth may also be added for each degree ot du-forence in the temperature.

Robison’s formula is nearly similar, h — ( 87 X -21 f)30

— d ±; 2.63 e;/being the mean temperature reckoned-V

fiorn the freezing point, y the mean height of the mercury,d the difference of the heights, in tenths, ami e the differ-ence ot the temperatures. Or we may take h — (2610 + 0/J(It r/cfc 2.8 e.)

It is said, that where the barometer rises or sinks in thecourse of the operation, the alteration is generally less at

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