CATALOGUE. — METEOROLOGY, BAROMETRICAL MEASUREMENTS. 473 



Barometrical experiments give ^ and j^. The specific 

 gravity of mercury at fl8° is 13-61. The decrease of gravity 

 in ascending from the earth's surface produces no percepti- 

 ble effect. Logarithms give fathoms at 31.24°. 



*Shuckburgh's compaiisoti of his rules with 

 GenPi-al Roy's. Ph. tr. 1778. 681. 



Thinks, that either Roy's rules or his own are sufficiently 

 accurate. 

 *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 01°, and at the equator near 

 0° : the difference may perhaps depend on moisture : the 

 .same cause appears to require a correction for the mean 

 height above the sea, of which a table is given, the cor- 

 rection for temperature being diminished about ^j for each 

 inch that the mean height of the barometer is below 30°. 

 After all possible corrections, the height of Moel Eilio came 

 out near ^ij too great : if Dcluc's rules had been employed, 

 the error would have been greater. 



Chiminello on barometrica] measurements. 



Roz. XIII. 457. 

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



S. 

 Magellan's description of barometers. 

 Magellan's barometer. Roz. XIX. 108,194, 



257,341. 

 Achard on measuring heights by boiling 



water. A. Berl. 17«2. 54. Roz. XXV. 287. 

 Dawie?i demoniium altitudine. Hague, 1783. 

 Pasumot. Roz,. XXIX. 13. 

 Trembley in Saussure Voyages. III. 

 Tieinbiey's remarks on Deluc. Roz. XXXII. 



87. XLII. 181. 

 Maifcr iiber das hohenmessen 8. Frank f. 



1787. 

 Mayer iiber die warme in lucksicht auf dem 



barometer. 8. Frankf. 1796. 

 *Playfair. Ed. tr. I. 87. 



Accurate calculations. 

 Saussure on the density of the air at different 



heights. Roz. XXXVI. 98. 

 Morozzo on the constitution of the air. Soc. 



Ital. VI. 221. 

 vot. II. 



for 



Gerstner and Gruber on the density of the 



air. Roz. XLI. 110. 

 Robison. Enc. Br. Art. Pneumatics. 

 Hamilton. Ir. tr. V. 117. 

 Wild on the influence of the wind. Zach, 



Eph. IV. 385. 

 Laplace Exposition da systeme du monde. 



Follows Deluc. 



Laplace Mecanique celeste. IV. 



Rhode liber die berechnung der berghohen 

 nacli Laplace. Halle, 1803. 



Berger's mode of bringing down air in bot- 

 tles, Journ. Phys. LVI. 366. 



,. ■ ■ , s» i3.(iie—y) . 



. Lambert gives A =10 000 1. — — — ■-- for the 



y SI 583 — y 



height in toisej, y being the height of the mercury in inches 



Fr. 



Deluc s rule is ft — 10 000 1. - | l -^ I 



l^ \ 484 / 



toises, / being the degrees of Fahrenheit. 



Maskelyne's rule deduced from Deluc'i is ft =: (10 000 1. 



(-\'^.ii'igj ( 1+'^^ )» «■ being the difference of 



the temperatures. Or, if we use a thermometer on which 

 the freezing point is at 0° and the boiling point at 81.4°, 

 for measuring the temperature of the meicury, and another 

 with the freezing point at —9°, and the boiling point at 191' 

 for that of the air, we shall have A iz (10000 1. ( -qzi ). 



(*^ + '\ 

 1 -I ), i being the difTerence of the mercurial tem- 

 1000/ 



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



Shuckburgh says, that for common practice, when the 

 height is lessthana mile, it is sufficient to allow 91.72 feet 

 for every tenth of an inch of difference, adding .211 f. for 

 each degree above 55", and increasing the whole in the ra- 

 tio of 30 inches to the mean height of the barometers. One 

 ten thousandth may also be added for each degree ot dit- 

 fcrence in the temperature. 



Robison's formula is nearly similar, ft~ (87X.21/) 



30 



— d ±: 2.83 e; /being the mean temperature reckoned 



from the freezing point, \j the mean height of the mercury, 

 d the difference of the heights, in tenths, and e the differ- 

 ence ot the temperatures. Or we may take ft r= (2810±0/} 

 d:yit 2.8c.) 



It is said, that where the barometer rises or sinkt in the 

 course of the operation, the alteration is generally less at 



Sp 



