344 O'^ t^^ Caufe of Earthquakes. 



in the Cordilleras, which extend along the South fca fi^bm 

 Chili to Panama. 



48. There are reckoned to be 30 or 35 volcanoes on the 

 coaft of New Spain which looks to\vards the fouth-weft on 

 the iide of the Pacific ocean. 



49.' The volcanoes (itiialed on lakes or deep giilphs, and 

 which have a narrow mouth, manifeft themfelves fometimes 

 differently. That of the lake of Nicaragua is fituated on an 

 ifland to the eaft of the ifl.hmus v\hich fqnarates that lake 

 from the South fea, or to the north-welt of the other parts 

 of the continent. 



50. Volcanoes are more violent after long and heavy rattis, 

 than after and during the time of drought. 



51. When rain falls in an equal quantity on all the parts 

 of a mountain, that which falls on the fummit muft naturally 

 run down and penetrate very little into the earth; while the 

 fides receive not only that of the heavens, but that alfo which 

 comes from the fummit. 



52. The fides of a mountain become plane in proportion 

 as they become lower, and to their difiance from the fummit. 



53. The lowed parts of the fides of a mountain mu^tie- 

 ceflfarily imbibe more water than the higher parts. The 

 quantity imbibed mufl be greater as the inclination of the 

 fides decreafes in approaching the bafe. 



54. In the interior part of fteep mountains there mufi be 

 places to which the water cannot penetrate. Thefe places, 

 in all probability, are thofe which approach nearell to the 

 vertical line, proceeding from the fummit and terminating 

 perpendicularly towards the middle of the bafe. 



55. If the filtration of rain water through the earth on the 

 fides of mountains flops up the pores, and if the fuhterranean 

 vapours do not find room to efcape through thefe fides, they 

 muft proceed towards thofe parts which approach the ver- 

 tical line drawn from the fummit, which is the place where 

 they can find a paflfage by foaklng through the pores of the 

 dry earth which muft be there found. 



56. If gas and fuhterranean fires are thrown towards the 

 axis of the mountain bv the intermiflion of waters which 

 flop up their otiiir paflTaces, the elafticity of thefe fluids ac- 

 cumulated at the centre muft neceffarilv increafe. It appears 

 that, from this obfervation, we may deduce the reafon why 

 volcanoes often break out after long continued rains. 



57. Whether it be the decompoiition of water, or any other 

 caufe, that makes the fire of volcanoes be difengaged, this 

 fire muft neceflarily, as already faid, purfue that route where 



it 



