labourers below at any one time. Very seldom are the miners within the sound of each other's operations, except occasionally when they hear the dull report of the explosions. In the vicinity of the main shaft, indeed, the incessant action of the huge chain of pumps, produces a constant, but not very loud noise, while the occasional rattling of the metallic buckets against the walls of the shaft, as they ascend and descend, relieves the monotony both of the silence and the sound. Still every thing is dreary, dull, and cheerless; and you can be with difficulty persuaded, even when in the richest and most populous mines, that you are in the centre of such extensive and important operations." For keeping the workings from being inundated, each mine is furnished with a chain of pumps, extending from the bottom to the _adit-level_, worked by a single pump-rod; each pump receiving the water brought up by the one immediately below it. All the water of the deepest level finds its way into the bottom of the mine, technically called the _Sump_, whence it is finally elevated to the adit, through which it flows by a gentle descent to the surface.[103] We have yet to notice a fact connected with the natural history of these subterranean recesses, which has lately excited a very considerable share of interest in the members of the Cornish Geological Society,--that _the natural temperature of the earth in these mines is considerably above that of the mean of the climate, and increases with the depth, at the rate of about one degree for every 50 or 60 feet_.[104] Does there exist then a permanent source of heat in the interior of the earth? The business of a mine is managed by a foreman, called the _Captain_, who keeps the accounts, and pays and regulates the miners; there are also _Under-ground Captains_, who have the immediate inspection of the works below. There exists a popular belief that the Cornish miner frequently lives under ground for many days, or weeks, without ever visiting the surface. This is never the case at any time, or under any circumstances. He does not even eat, much less sleep, in the mine, but returns _to grass_, and to his home, often many miles distant, at whatever depth he may have been working, when relieved from his labours.