EVAPORATION AND CONDENSATION. 289 



tained still more vapour ; while at 60 the quan- 

 tity was yet farther augmented. He also found 

 that when the temperature of the flask was 

 suddenly reduced from 60 to 40, a portion of 

 vapour was converted into water, and that the 

 quantity retaining the elastic form was precisely 

 the same as when the temperature^ 

 nally at 40. 



The above is a simple and be^5IiUiIlfepp&SI ' Y^ 

 sentation of what is perpetually goinj 

 out the atmosphere, and in the steam 



By another series of admirable experiments, 

 he ascertained that the quantity and elastic force 

 of vapour, whether formed in vacuo, or under the 

 pressure of the atmosphere, are the same, and 

 determined by temperature alone the differ- 

 ence being this, that in the latter case the pro- 

 cess goes on much more slowly, because the 

 atmosphere presents a mechanical impediment 

 to its diffusion somewhat analogous to the ob- 

 struction of water by porous sand. From which 

 he inferred that vapour is not chemically united 

 with the air, as had been formerly supposed, 

 but mechanically diffused through it, forming 

 a distinct atmosphere of its own, the elastic 

 force of which is always in proportion to tem- 

 perature. 



At he found the quantity and elastic force 

 of vapour equal to the pressure -064 inch of 

 mercury that is, about -^ of an inch. At 32 



u 



