DE LUC AND MURPHY. 301 



It is stated by Humboldt and others, that within 

 the tropics during the rainy season, the first in- 

 dication of an approaching storm is generally a 

 light wind, with a few scudding clouds, but that 

 when it begins to lighten, the whole sky is sud- 

 denly obscured by dense clouds that immedi- 

 ately descend in torrents of rain. 



That atmospheric electricity is a constituent 

 of aqueous vapour, will appear from the descrip- 

 tion of a thunder storm among the Alps, as re- 

 corded by the celebrated De Luc. He states 

 that it commenced with abundant discharges of 

 electricity from dry transparent air, which con- 

 tained neither vapours nor the electric fluid, but 

 the constituents of both, and that clouds were 

 suddenly formed around the summit of the Buet, 

 during each explosion. In other words, that si- 

 multaneous with the discharges of lightning from 

 dry transparent air, was the sudden formation of 

 clouds, and precipitation of rain. 



From another portion of De Luc's work, en- 

 titled, Idces sur la Meteor ologie, it is obvious that 

 he mistook transparent aqueous vapour for " dry 

 air." He supposed that clouds were formed by 

 the union of oxygen and hydrogen gases by the 

 agency of electricity, as water is generated by 

 passing an electric spark through them.* 



* This hypothesis has been revived by Mr. Murphy of Cam- 

 bridge, in a recent work on Electricity, the professed object of 

 which is to reduce the science to mathematical laws. Had this 

 ingenious author traced the history of rain from the first process 



