494 ANNUAL REGISTER, 1814. 



under the tropics. I have verified 

 this observation at Cumana, at Li- 

 ma, and ut Riobamba ; and it is so 

 much the more worthj- of fixing 

 the attention of natural philoso- 

 phers, as at St. Domingo, at the 

 town of Cape Francois, it is asserted 

 that a water barometer was observ- 

 ed to sink two inches and a half 

 immediately before the earthquake 

 of 1770. In the same manner it 

 is related, that, at the time of the 

 destruction of Oran,a druggist fled 

 with his family, because, observing 

 accidentally, a few minutes before 

 the earthquake, the height of the 

 mercury in his barometer, he per- 

 ceived that the column sunk in an 

 extraordinary manner. I know not 

 whether we cangivecredittothisas- 

 sertion: butasitisnearlyimpossible 

 to examine the variations of the 

 weight of the atmosphereduringthe 

 shocks, we must be satisfied in ob- 

 serving the barometer before or af- 

 ter these phaenomena have taken 

 place. In the temperate zone, the 

 aurora borealis does not always mo- 

 dify the variation of the needle, 

 and the intensity of the magnetic 

 forces. Perhapsalsoearthquakesdo 

 not act constantly in the same man- 

 ner on the air that surrounds ns. 



We can scarcely doubt, that the 

 earth, when opened and agitated by 

 shocks, spreads occasionally gase- 

 ous emanations through the at- 

 mosphere, in places remote from 

 the mouths of volcanoes not extinct. 

 At Cumana, as we have already ob- 

 served, flames and vapours mixed 

 with sulphurous acid spring up 

 from the most arid soil. In other 

 parts of the same province, the 

 earth ejects water and petroleum. 

 At Riobamba a muddy and inflam- 

 mable mass, which is called mot/a, 

 issues from crevices that close 



again, and accumulates into ele- 

 vated hills. At seven leagues from 

 Lisbon, near Colares, during the 

 terrible earthquake of the first of 

 November, 1755, flames and a co- 

 lumn of thick smoke were seen to 

 i.>.sne from the flanks of the rocks 

 of Alvidras, and, according to some 

 witnesses, from the bosom of the 

 sea. This smoke lasted several days, 

 and it was the more abundant in 

 proportion as the subterraneous 

 noise, which accompanied the 

 shocks, was louder. 



Elastic fluids thrown into the at- 

 mosphere may act locally on the 

 barometer, not by their mass, 

 which is very small, compared to 

 the mass of the atmosphere ; but 

 because, at the moment of the 

 great explosions, an ascending cur- 

 rent is probably formed, which di- 

 minishes the pressure of the air. — 

 I am inclined to think, that in the 

 greater part of earthquakes nothing 

 escapes from the agitated earth ; 

 and that, where gaseous emana- 

 tions and vapours take place, they 

 oftener accompany, or follow, than 

 precede the shocks. This last cir- 

 cumstance explains a fact, which 

 seems indubitable. I mean that 

 mysterious influence, in equinoctial 

 America, of earthquakes on the 

 climate, and on the order of the 

 dry and rainy seasons. If the earth 

 generally act on the air only at the 

 moment of the shocks, we can con- 

 ceive why it is so rare, that a sen- 

 sible meteorological change be- 

 comes the presage of these great 

 revolutions of nature. 



The hypothesis according to 

 which, in the earthquakes of Cu- 

 mana, elastic fluids tend to escape 

 from the surface of the soil, seems 

 confirmed by the observation of 

 the drieadful noise, which is heard 



