AND EXTERNAL RESISTANCE. 283 



iierves, are far stronger when they are directed 

 from the bottom to the top, than from the top to 

 the bottom; if it were not, therefore, for the 

 ascent of the atmosphere, the pulsations of the 

 air, would increase in force, in proportion as 

 they were conveyed downwards, through a 

 more expansible medium. Sound, from the 

 top to the bottom, is similar to what is expe- 

 rienced by those who speak against the wind. 

 The ascent of the atmosphere is an opinion 

 which is further strengthened by the observa- 

 tions made by MONS. CHARLES, in the car of 

 his balloon, at the time he was at the elevation 

 of 9,000 feet from the surface of the earth : he 

 observed, with great surprise, that the stream- 

 ers of his banners pointed upwards ; which, he 

 says, could not be the effect of the ascent, or 

 descent, of the balloon, as it was moving at the 

 time in an horizontal direction. 



That a regular and progressive diminution 

 takes place of the atmospheric column, from 

 bottom to top, is proved by facts the most deci- 

 sive and satisfactory that can be devised ; it is 

 proved by the change which is produced on a 

 small quantity of atmospherical air, taken near 

 the surface of the earth, and carried in a blad- 

 der to the highest point of elevation ; -the air 

 in the bladder is gradually found to dilate 

 and expand, as it does under an exhausted 

 receiver; insomuch, that the bladder which 



