40 A HISTORY OF 



mines, being naturally cold,* send forth a degree of coldness to the 

 external air, to comfort and refresh it: on the contrary, metallic mmes 

 are known, not only to warm it with their exhalations, but often ii 

 destroy all kinds of vegetation hy 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.t The inhabi 

 tants, also, are rendered dreadfully sensible of these subterraneous 

 exhalations, being affected with such a variety of evils proceeding en- 

 tirely from this cause, that books have been professedly written upon 

 this class of disorders. 



Nor are these vapours, which thus escape to the surface of the earth, 

 entirely unconfined; 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 travellers, 

 lies within four miles of Naples, and is situated near a large lake 

 of clear and wholesome water.J 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 peasants that 

 necessity compels to reside there, looking quite consumptive and ghast- 

 ly, 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 fhe purpose of showing the 

 experiment to the curious. These poor animals always seem perfect- 

 ly sensible of the approach of a stranger, and endeavour to get out 

 of the way. However, their attempts 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 observer can see no visible mark of its pestilential va- 

 pour ; onlv to about a foot from the bottom, the wall seems to be 

 tinged with a colour resembling that which is given by stagnant wa- 

 ters. When the dog, this poor philosophical martyr, as some have 

 called him, is held above this mark, he does not seem to feel the small- 

 est 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 injury 



This vapour, which thus for a time suffocates, 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 ap- 

 proach 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, 



Phil, Trans, vol. ii. p. 523. f Boyle, vol. Hi. \>. 238 



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



