OPINIONS OF LUCRETIUS. 317 



extremely vague and imperfect, and that its re- 

 lations to the caloric of evaporation have scarcely 

 been inquired into. On the other hand, it is 

 equally evident, that if we analyse the pheno- 

 mena of evaporation and condensation, as they 

 are constantly going on before all eyes, we obtain 

 a simple and satisfactory solution of the problem. 

 The fact which was announced by Dalton, that 

 caloric is the only cause of evaporation, taken in 

 connexion with another fact, that aqueous vapour 

 is condensed into rain or hail, ivith a rapidity pro- 

 portional to the amount of lightning, are decisive 

 in regard to the convertibility of caloric into 

 electricity, which, as will be seen hereafter, com- 

 pletely explains the phenomena of hurricanes, 

 tornados, &c. 



The ideas of the ancient Greek philosophers, 

 which were derived from observation without ex- 

 periments, were more in accordance with nature 

 and reason than the hypotheses of modern times. 

 It was maintained by Lucretius, who gives the 

 doctrines of Epicurus, that lightning consisted of 

 fire alone, and that it was derived from the sun. 

 He represents the igneous particles of fluid as 

 rushing to a focus, by which concentration they 

 acquire the power of instantaneously fusing me- 

 tals.* (De Natura Rerum, Lib. vi. 108.) That 



* He further states, that it is by the meeting of warm and cold 

 air that they are elicited. It is not very obvious how this subtile 

 matter becomes concentrated into a ball of fire on quitting a mass 

 of vapour ; but such is the fact. It is equally difficult to explain 



