302 SENECA AND THE STOICS. 



According to Seneca, the ancient stoics taught 

 a similar doctrine " that air was converted into 

 fire and water," during a thunder storm : (Na- 

 tural Questions, Book ii.) from which it would 

 appear, that they were ignorant of the process 

 of evaporation, by which water is expanded into 

 elastic vapour like air ; or that they confounded 

 the one with the other. 



In the 22nd chapter of the same book, in 

 which Seneca gives his own opinion, he main- 

 tains that^Ve and lightning are the same, because 

 the latter produces the same effects as fire, such 

 as the heating and melting of metals, the com- 

 bustion of forests, &c. ; but that in lightning, fire 

 was greatly condensed. 



But to return from this digression, if it be 

 true that caloric is the cause of evaporation, (as 

 proved by De Luc himself,) and if transparent 

 vapour be suddenly condensed into clouds and 

 rain, with a rapidity proportional to the amount of 

 lightning, the conclusion is inevitable, that solar 



of evaporation, he would probably not have maintained that 

 heavy showers of rain which accompany lightning, may be pro- 

 duced from the combination of oxygen and hydrogen by elec- 

 tricity, after it had been demonstrated by Dalton that vapour 

 or steam is composed of water and caloric, and that its con- 

 densation is owing to the evolution of caloric, whether attended 

 with lightning or not. The supposition of Dr. Darwin was more 

 consistent, who maintained that electricity was the cause of 

 evaporation, because discharges of lightning are attended with 

 rapid precipitations of rain. 



