BECCAR1A, FRANKLIN, AND VOLTA. 305 



Scarcely one of the older writers on meteo- 

 rology, clearly understood the simple process of 

 evaporation. Beccaria supposed that the earth 

 was full of electric matter, which rises to the 

 upper regions of the atmosphere, carrying with 

 it water in the form of vapour. (Priestley's Hist. 

 of Electr. p. 340.) 



Franklin also supposed, that vapour was ele- 

 vated from the sea, by the united agency of heat 

 and electricity. But it is now well established, 

 that caloric is the vaporizing agent all over the 

 world that wherever there is heat and water in 

 sufficient quantity, vapour is produced, whether 

 from the ocean, fresh water lakes and rivers, or 

 from the surface of the dry land and that other 

 things being equal, its amount, like that of light- 

 ning, is determined by temperature. Had Frank- 

 lin clearly understood the process of evaporation, 

 and traced the connexion between discharges of 

 lightning and precipitation, he would probably 

 have added to his discovery of the identity of 

 lightning and common electricity, the still more 

 important fact, that caloric and electricity are 

 different manifestations of the same potent ele- 

 ment. 



The celebrated Volta adopted the opinion of 

 Franklin, with some slight variation. He sup- 

 posed that all bodies contained electricity, a 

 portion of which was evolved whenever they un- 

 derwent a change of state ; that when water was 



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