BOOK in. CHAP. VII. 617 



of the air by dny and night, their terror excited by the calamity, their 

 anxiety for the lofs of goods, relations, or friends, dcflroytd, con- 

 ftant dejedlion of fpirits, and want of neceliary conveniences for health, 

 it is no wonder that, under the concurrence of thefe circumftances, they 

 fliould contra6l ficknefs, that the fymptoms (hould be aggravated to a 

 degree of contagion, and thus fpread almoft univerfally through a 

 country. 



S E C T. V. ' 



EARTHQUAKES. 



A ferles of dry weather for five, fix, or feven months, in this ifland, 

 generally terminates, either in an earthquake, or a gult of wind and 

 rain, attended with or without thunder. 



Earthquakes ufually happen immediately after the firft fall of heavy 

 rain, fucceeding a drought. 



The weather is always extremely fultry, clofe, and ftill, juft before 

 an earthquake, or before ftrong breezes, violent Norths, or heavy rains. 



Earthquakes feldom, if ever, happen in windy weather. 



They are fucceeded here with fqualls of wind and rain, fometimes 

 accompanied with thunder (but more ufually without) and fometimes 

 with a brutum fulinen. When frequent fmall fliocks happen, there is 

 lefs of thunder and lightning than at any other times ; and it has been 

 remarked, that when thunder and lightning happen after earthquakes, 

 the fhocks from that time either difcontinue, or become fainter and 

 fainter. 



All fhocks are horizontal ; none have ever been known to a6l in a 

 perpendicular direftion. 



Hence it has been fuppofed, on very probable grounds, that the air 

 is more often the vehicle of the fhock than has generally been imagined : 

 and that the eleclric fluid, which pervades all nature ; and, when 

 put in motion, is equal to the moft violent efFefts ever knovi^n to hap- 

 pen from earthquakes, is a principal agent in caufing them. But other 

 principles may alfo lend their aid. In its fubterrapeous progrefs it may 

 enkindle inflammable matter, and generate a rarefied vapour of immenfe 

 power [«]. The vapour feems to endeavour by every means to get 

 vent ; and, pafling by fubftances of folidlty fufficient to divert it, fecks 

 an eafier courfe through fandy and other X\'^\X.Jiratd, which make lefs 

 refiftance ; and at length burfts forth into the atmofphere. 



Hence buildings, erecSted on a rocky foundation, are fubje£l to be 

 lefs Injured by them than thofe which are built on other foils ; and 

 more particularly thofe which Hand on a loofe fandy texture, contigu- 

 ous to the fea. 



[»] Water turned into vapour is faid to occ.tpy 14,000 tiincs its former fpace. 



Vol. II. 4 K No 



