THE 



PHILOSOPHICAL MAGAZINE 

 AND JOURNAL. 



3P' AUGUST 1825. 



XL On the Constitution of the Atmosphere. By J. Ivory, Esq. 

 M.A. F.R.S. 



1. TT is well known that, as we ascend in the atmosphere, 



-■• a continually increasing degree of cold is found to 

 prevail. There are no doubt irregularities and exceptions. 

 Particularly, in small heights near the earth's surface, the cold 

 is sometimes greater below than above. But in general, and 

 at great heights beyond the immediate influence of the earth, 

 the fact cannot be contested. 



This peculiar disposition of heat in the atmosphere has not 

 been much inquired into. The account of it proposed by 

 Dalton is the only one which seems deserving of notice. Ac- 

 cording to that philosopher, a given mass of air, whatever be 

 its place in the atmosphere, retains always the same absolute 

 quantity of heat. When it ascends and becomes rarer by di- 

 minished pressure, the cold produced, or the heat which dis- 

 appears from the thermometer, enters into combination with 

 the dilated air. On the other hand, when it descends, the 

 condensation produced by the greater pressure causes it to 

 give out part of the heat combined with it in a latent form, 

 which becomes sensible to the thermometer. If we conceive 

 a peipendicular column of air extending from the earth's sur- 

 face to the top of the atmosphere to be divided into equal 

 masses, the respective portions will successively occupy larger 

 spaces ; and, according to the principle of Dalton, we shall 

 have a gradation of heat decreasing upwards as observation 

 requires. 



In all our inquiries into the properties of the atmosphere, it 

 is supposed that the height of a mass of air, its pressure, its 

 density, and its temperature are all intimately connected. A 

 change in one of these four things is necessarily attended with 

 a variation of all the rest. When the height increases, the 

 pressure, the density, and the temperature decrease : and a 

 mass of air cannot remove to a lower place, without receiving 

 an augmentation of pressure, density, and temperature. As 



Vol. Gf). No. f528. y///ir- 1825. ' L there 



