THE EARTH. 



25 



reach the surface, and there put on various 

 appearances. In (act, much of' the salubrity, 

 and much of the unwholesomeness, of climates 

 and soils, is to be ascribed to these vapours, 

 which make their way from the bowels of the 

 earth upwards, and refresh or taint the air 

 with their exhalations. Salt mines, being na- 

 turally cold," send forth a degree of coldness 

 to the external air, to comfort and refresh it : 

 on the contrary, metallic mines are known, 

 not only to warm it with their exhalations, 

 but often to destroy all kinds of vegetation by 

 their volatile corrosive fumes. In some mines, 

 dense vapours are plainly perceived issuing 

 from their mouths, and sensibly warm to the 

 touch. In some places, neither snow nor ice 

 will continue on the ground that covers a 

 mine ; and over others the fields are found 

 destitute of verdure. b The inhabitants, also, 

 are rendered dreadfully sensible of these sub- 

 terraneous exhalations, being affected with 

 such a variety of evils proceeding entirely 

 from this cause, that books have been pro- 

 fessedly written upon this class of disorders. 



Nor are these vapours, which thus escape 

 to the surface of the earth, entirely uncon- 

 fined ; for they are frequently, in a manner, 

 circumscribed to a spot. The grotto Del 

 Cane, near Naples, is an instance of this; 

 the noxious effects of which have made that 

 cavern so very famous. This grotto, which 

 has so much employed the attention of tra- 

 vellers, lies within four miles of Naples, and 

 is situated near a large lake of clear whole- 

 some water. c Nothing can exceed the beauty 

 of the landscape which this lake affords; being 

 surrounded with hills covered with forests of 

 the most beautiful verdure, and the whole 

 bearing a kind of amphitheatrical appearance. 

 However, this region, beautiful as it appears, 

 is almost entirely uninhabited ; the few pea- 

 sants that necessity compels to reside there, 

 looking quite consumptive and ghastly, from 

 the poisonous exhalations that rise from the 

 earth. The famous grotto lies on the side of 

 a hill, near which place a peasant resides, 

 who keeps a number of dogs for the purpose 

 of showing the experiment to the curious. 

 These poor animals always seem perfectly sen- 

 sible of the approach of a stranger, and endea- 

 vour to get out of the way. However, their at- 



Phil. Trans. voL ii. p. 523. b Boyle, vol. iii. p. 238. 



tempts being perceived, they are taken and 

 brought to the grotto ; the noxious effects of 

 which they have so frequently experienced. 

 Upon entering this place, which is a little 

 cave, or hole rather, dug into the hill, about 

 eight feet high, and twelve feet long, the ob- 

 server can see no visible mark of its pestilen- 

 tial vapour; only to about a foot from the 

 bottom, the wall seems to be tinged with a 

 colour resembling that which is given by 

 stagnant waters. When the dog, this poor 

 philosophical martyr, as some have called 

 him, is held above this mark, he does not 

 seem to feel the smallest inconvenience ; but 

 when his head is thrust down lower, he strug- 

 gles to get free for a little ; but in the space 

 of four or five minutes he seems to lose all 

 sensation, and is taken out seemingly without 

 life. Being plunged in the neighbouring lake, 

 he quickly recovers, and is permitted to 

 run home, seemingly without the smallest in- 

 jury. 



This vapour, which thus for a time suffo- 

 cates, is of the humid kind, as it extinguishes 

 a torch, and sullies a looking-glass ; but there 

 are other vapours perfectly inflammable, and 

 that only require the approach of a candle to 

 set them blazing. Of this kind was the burn- 

 ing well at Brosely, which is now stopped up ; 

 the vapour of which, when a candle was 

 brought within about a foot of the surface of 

 the water, caught flame like spirits of wine, 

 and continued blazing for several hours after. 

 Of this kind, also, are the perpetual fires in 

 the kingdom of Persia. In that province, 

 where the worshippers of fire hold their chief 

 mysteries, the whole surface of the earth, 

 for some extent, seems impregnated with in- 

 flammable vapours. A reed stuck into the 

 ground continues to burn like a flambeau; a 

 hole made beneath the surface of the earth, 

 instantly becomes a furnace, answering all 

 the purposes of a culinary fire. There they 

 make lime by merely burying the stones in 

 the earth; and watch with veneration the 

 appearances of a flame that has not been ex- 

 tinguished for times immemorial. How dif- 

 ferent are men in various climates ! This de- 

 luded people worship these vapours as a 

 deity, which in other parts of the world are 

 considered as one of the greatest evils. 



c Kircher, Mund. Subt. vol. i. p. 191. 



