[ 487 ] 



The only objedion to this theory, which may at firft view 

 appear plaufible, is, that the quantity of fmoke elevated to the 

 greateft height during volcanic eruptions does not produce a haze 

 of a firi.ilar nature and extent ; yet on confideration it appears to 

 me of no weight ; for, i ^ T he eledlricity of this fmoke is de- 

 ftroyed during the eruption by the frequent flaflies of lightning 

 that take place in the body of the fmoke during its afccnt, and 

 confume the hydrogen and bituminous particles ; and, 2do. This 

 fmoke then confifts chiefly of heated air, impregnated with in- 

 cinerated carbonic particles, and not of metallic particles of which, 

 it is not a folvent; and as the colder ambient air prefles towards 

 the volcano and the heated fmoke, its diffufion is prevented, 

 and never, unlefs by a florm. are its particles carried farther than 

 20 or 30 miles. See Hiftoire de Vefuve par Padre della Torre, 

 p. 127, &c. 



Section, IV. 



Of Rain. 



DtMiNUTioN of the temperature of air, repjcte with moif- 

 ture, below the degree at which its faturation takes place, 

 whether this refrigeration were caufed by rarefadtion, or by 

 the nterrnixture with colder air, has been generally fuppofed 

 the caufe of rain ; but this hypothefis in both its branches 



3 P 2 has 



