562 HISTORY OF THERMOTICS. 



therefore, the introduction of the notion of the 

 chemical solution of water in air was apparently 

 very successful. But its defects are of a very fatal 

 kind ; for it does not at all apply to the facts which 

 take place when air is excluded/ 



In Sweden, in the mean time 5 , the subject had 

 been pursued in a different, and in a more correct 

 manner. Wallerius Ericsen had, by various experi- 

 ments, established the important fact, that water 

 evaporates in a vacuum. His experiments are clear 

 and satisfactory; and he inferred from them the 

 falsity of the common explanation of evaporation 

 by the solution of water in air. His conclusions 

 are drawn in a very intelligent manner. He con- 

 siders the question whether water can be changed 

 into air, and whether the atmosphere is, in conse- 

 quence, a mere collection of vapours ; and on good 

 reasons, decides in the negative, and concludes the 

 existence of permanently-elastic air different from 

 vapour. He judges, also, that there are two causes 

 concerned, one acting to produce the first ascent 

 of vapours, the other to support them afterwards. 

 The first, which acts in a vacuum, he conceives to 

 be the mutual repulsion of the particles ; and since 

 this force is independent of the presence of other 

 substances, this seems to be a sound induction. 

 When the vapours have once ascended into the air, 

 it may readily be granted that they are carried 

 higher, and driven from side to side by the cur- 



5 Fischer, Gesch. Phys. vol. v. p. 63. 



