THE EARTH. 



23 



ceived below, without the necessity of recur- 

 ring to the central heat for an explanation. 



Hence, therefore, there are two principal 

 causes of the warmth at the bottom of mines : 

 the heat of the substances of which the sides 

 are composed ; and the want of renovation in 

 the air below. Any sulphureous substance, 

 mixed with iron, produces a very great heat, 

 by the admission of water. If, for instance, a 

 quantity of sulphur be mixed Avith a propor- 

 tionable share of iron filings, and both kneaded 

 together into a soft paste, with water, they 

 will soon grow hot, and at last produce a 

 flame. This experiment, produced by art, 

 is very commonly effected within the bowels 

 of the earth by nature. Sulphurs and irons 

 are intimately blended together, and want 

 only the mixture of water or air to excite 

 their heat ; and this, when once raised, is 

 communicated to all bodies that lie within 

 the sphere of their operation. Those beau- 

 tiful minerals called marcasites and pyrites, are 

 often of this composition ; and wherever they 

 are found, either by imbibing the moisture of 

 the air, or having been by any means com- 

 bined with water, they render the mine con- 

 siderably hot. a 



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 assistance 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 dis- 

 tance from the mouth of the pit where they 

 are at work, another pit, which joins the for- 

 mer 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 be- 

 comes, as Mr. Boyle affirms, very commodious 

 for respiration, and also very temperate as to 

 heat and cold. b Mr. Locke, however, who has 

 left us an account of the Mendip mines, seems 

 to present a different picture. " The descent 

 into theseisexceedinglydifficult and dangerous; 

 for they are not sunk like wells, perpendicu- 

 larly, but as the crannies of the rocks happen 

 to run. The constant method is to swing down 



Kircher Mund. Subt. vol. ii. p. 216. 

 k Boyle, vol. iii. p. 238. 



by a rope placed under the arms, and clam- 

 ber 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 to the windy side, or laid over 

 the mouth of the hole, the miners below pre- 

 sently want breath, and faint; and if sweet- 

 smelling flowers chance to be placed there, 

 they immediately lose their fragrancy, and 

 stink like carrion." An air so putrefying can 

 never be very commodious for respiration. 



Indeed, if we examine the complexion of 

 most miners, we shall be very well able to 

 form a judgment of the unwholesomeness of 

 the place where they are confined. Their 

 pale and sallow looks show how much the 

 air is damaged by passing through those deep 

 and winding ways, that are rendered humid 

 by damps, or warmed with noxious exhala- 

 tions. But although every mine is unwhole- 

 some, all are not equally so. Coal-mines are 

 generally less noxious than those of tin ; tin 

 than those of copper ; but none are so dread- 

 fully destructive as those of quicksilver. At 

 the mines near the village of Idra, nothing 

 can adequately describe the deplorable in- 

 firmities of such as fill the hospital there; 

 emaciated and crippled ; every limb con- 

 tracted or convulsed, and some in a manner 

 transpiring quicksilver at every pore. There 

 was one man, says Dr. Pope, c who was not in 

 the mines above half a year, and yet whose 

 body was so impregnated with this mineral, 

 that putting a piece of brass money in his 

 mouth, or rubbing it between his fingers, it 

 immediately became as white as if it had 

 been washed over with quicksilver. In this 

 manner all the workmen are killed sooner or 

 later; first becoming paralytic, and (hen 

 dying consumptive : and all this they sustain 

 for the trifling reward of seven pence a day. 



But these metallic mines are not so noxious 

 from their own vapours, as from those of the 

 substances with which the ores are usually 

 united, such as arsenic, cinnabar, bitumen, or 

 vitriol. From the fumes of these, variously 



c Phil. Trans, vol. ii. p. 578. 

 H 



