Ch. vil south AMEHICA. 89 



and fire exist only at the instant ^vl^cn the matter bc- 

 coines incaaied, 2ind the air spreading: itself thro ug^h 

 all the veinSj the liglit is cytin:;-uished by its diiata- 

 tion, and becomes afterwards impciceptible. It is 

 netessarv to snppos<^ ihatth,'^re ¡r.iist be ^ome, th 'iigh 

 a short inierval^ between the infLmimatinn and cííect. 

 Neither is the fla* le permanente the substance ig- 

 liit^d not containing- those solid and oleagi.ioiis par- 

 t;c'es whi'.h supply the volcanoes. Besides, they arc 

 not in suñxi?nt quantity id ascend from ihe subter- 

 raneous caverns \\here they tooiv ñ:e ¡o t'le supcr- 

 iicies of the earth. Farther, tiiis not betugthf^ place 

 where the matter was orig'iiially contained, bat that 

 where it has forced a passage forthe quantity of air 

 which its rarefactic-n augmented, the first light is lost 

 among the meanders of its course, and therefore not 

 Í!> be seen when the wind violently forces a passage. 

 Tiierc have, however, been instances when the light 

 has been seen, tbouiih much oi'tener the smoke ; but 

 this is £;enerallv loi,t in the clouds of uust ascenuiiiir 

 at the time of the concussion. 



The shocks are repeated at intervals, of a few 

 days, sometimes of a few hours ; proceeding from 

 the matter being dispersed in difterent places, and 

 each in a diiferent degree of aptitude for inilam- 

 maiion, one part kindling after another sucessivc- 

 ly, as each is more fir less prepared. Hence proceed 

 also the düferejit violence of the shocks and the 

 different intervals of time For the quantity first in- 

 flamed increases, by its heat, otlier infíammable 

 portions of matter ; whence a part which would not 

 have been ignited till after some days, by nicaas of this 

 adventitious fire, becomes so within a few hours. The 

 second shocks are more violent, and cause a greater 

 • estruction than the first ; for tiie fire of the poriion 

 of matter wdiich is first infiamed, though in itself 

 sniall, is suiiicient to 'accelerate tiie fermentation of 



a much 



