AND EXTERNAL RESISTANCE. 287 



gressive diminution in the density of the atmos- 

 phere, from the bottom to the top ; I shall now 

 proceed to prove, that the increased power of 

 expanding which the atmosphere possesses, 

 from the top to the bottom, does not proceed 

 from the weight of the superincumbent column. 

 In order to make the case as clear as possible, 

 I shall trace back my steps, and proceed in an 

 inverse order to that which I have hither pursued. 

 1. If a cubic foot of rarified air, at the highest 

 points of elevation, were received and inclosed 

 in a bladder of the same dimension, and carried 

 to the bottom ; it will be found to undergo a 

 change the very opposite, to that which a blad- 

 der half full of air, taken near the surface, was 

 found to do, when it was carried to high points 



placed in the receiver and the air which the receiver con- 

 tained exhausted out of it. Although the depression of the 

 mercury at different points of elevation, is not a test of the 

 different degrees of weight which the atmosphere possesses, it 

 certainly is of the progressive diminution of the expansible 

 power; and as it takes place in a manner which appears 

 (under the same state of the atmosphere) to be very regular 

 and progressive we may, from thence, employ the fall of the 

 mercury, as a measure of different degrees of elevation. The 

 conclusions which were made respecting the weight, will be 

 the same, as if they had been made to prove the difference of 

 expansible power ; the only difference will be, that the con- 

 clusion in the one case will be from a true, instead of pro- 

 ceeding from false principles. 



