THE EARTH. 69 



moisture of the air, or having been by any 

 means combined with water, they render the 

 mine considerably hot.* 



The want of fresh air, also, at these depths, is, 

 as we have said, another reason for their being 

 found much hotter. Indeed, without the assist- 

 ance of art, the bottom of most mines would, 

 from this cause, be insupportable. To remedy 

 this inconvenience, the miners are often obliged 

 to sink, at some convenient distance from the 

 mouth of the pit where they are at work, another 

 pit, which joins the former below, and which, in 

 Derbyshire, is called an air-shaft. Through 

 this the air circulates ; and thus the workmen are 

 enabled to breathe freely at the bottom of the 

 place ; which becomes, as Mr Boyle affirms, very 

 commodious for respiration, and also very tem- 

 perate as to heat and cold.t Mr Locke, how- 

 ever, who has left us an account of the Mendip 

 mines, seems to present a different picture -IT 

 " The descent into these is exceedingly difficult 

 and dangerous ; for they are not sunk like wells, 

 perpendicularly, but as the crannies of the rocks 

 happen to run. The constant method is to swing 

 down by a rope placed under the arms, and 

 clamber along by applying both feet and hands 

 to the sides of the narrow passage. The air is 

 conveyed into them through a little passage that 

 runs along the sides from the top, where they set 

 up some turfs, on the lee-side of the hole, to catch 

 and force it down. These .turfs being removed 



* Kircher, Mund. Subt. vol. ii. p. 216. f Boyle, vol. iii. p. 238. 



