288 ATMOSPHERIC ELECTRICITY. 



Heat and Electricity, that " the formation of 

 vapour seems to be connected with electricity, 

 though in what way we have no conception, and 

 that the change of vapour into clouds is pro- 

 bably connected with electrical phenomena not 

 understood." (Page 275, and elsewhere.) He 

 adds, that " the formation of rain is still in- 

 volved in impenetrable obscurity." 



It is also observed by Professor Forbes, that 

 on the noble science of atmospheric electricity, 

 almost every thing has yet to be done. (Trans- 

 actions of the British Association, Vol. I. p. 252.) 



As the phenomena of lightning have been 

 universally known to be immediately implicated 

 with the production of rain, it becomes neces- 

 sary to present an outline of the leading facts 

 connected with evaporation, previous to entering 

 upon the history of atmospheric electricity. 



That caloric is the true and only cause of 

 evaporation, or the formation of steam, is one 

 of those self-evident propositions which would 

 seem to require no proof. But to remove all 

 doubts upon the subject, the fact has been ex- 

 perimentally demonstrated by Dr. Dalton, to 

 whom the science of chemistry and meteorology 

 is so largely indebted. 



He put a little water in a dry glass flask, with 

 a thermometer in it, when he found that a small 

 quantity of vapour was formed at 32 F. At 

 40 the amount was increased : at 50 it con- 



