AEROSTATICS. 249 



much the more convenient. LA PLACE has intro- 

 duced a correction, on account of the difference of 

 the intensity of gravity in different latitudes; it is 

 found by multiplying the approximate height into 

 .0028371 X cos 2 lat. ; and is additive, when the la- 

 titude is less than 45; subtractive, when greater. 

 The same correction may be applied, in the same 

 manner, whatever formula is used. 



The fact, that the mercury in the barometer sinks on 

 ascending into the atmosphere, was first suggested 

 by PASCAL, and ascertained by experiments under 

 his direction. The application of this to the mea- 

 surement of heights, was made in France by MA- 

 RIOTTE, and in England by HALLEY. It remain- 

 ed, however, very imperfect, till DE Luc applied 

 the corrections for heat, and directed simultaneous 

 observations to be made at the top and bottom of 

 the mountain. He fell into some errors, which were 

 pointed out by TREMBLEY, and afterwards correc- 

 ted by the observations and experiments of Sir 

 GEORGE SHUCKBURGH and General ROY. LA 

 PLACE has, more lately, made barometrical mea- 

 surement the subject of his researches, and has given 

 the formula mentioned above. 



See DE Luc, Recherches sur les Modifications de T At- 

 mosphere. HORSELY and MASKELYNE, Phil Trans. 

 vol. LXIV. p. 214, & 158. TREMBLEY, apud SAUS- 

 SURE, vol. ii. p. 616. DAMEN, Dissertatio Phys. # 

 Math, de Montium Altitudinc^ Barometro metienda, 

 Hague, 1783. General ROY, Phil Tram. vol. LXVII. 

 (1777,) p. 653, &c. Sir GEORGE SHUCKBURGH, ibid. 



513, 



