Page:Whymper - Scrambles amongst the Alps.djvu/96

 clouds of smoke, the light of an ordinary miner's lamp could not be perceived at the distance of five or six yards, and respiration was difficult, for the atmosphere was vile. This was the end of the finished work: it is from hence that the air is drawn by the pumping-engines at the mouth, and it is hereabouts that all the foul vapours naturally accumulate and hang. The great vault was no longer overhead, but the way was reduced to a drift eight or nine feet wide and scarcely as much high, encumbered with waggons filled with débris, between which and the walls one could barely pass. In a hundred feet or so, we emerged—comparatively speaking—into a blaze of light. Two hundred greasy, smoky, but still light-giving lamps, hung from the walls. Drops of water flashed past them like gems. Two hundred men toiled at the enlargement of the gallery—bearded, grimy men, some on their backs, some on their sides, some working overhead, some half naked, some quite naked—all tapping laboriously at their mining-rods, and all perspiring profusely. The temperature had risen to 81½°. The multitude of the lights, the crowd of men, and the obscurity of the smoke, help to make the tunnel look an immense size—in fact, at this part, it is sometimes but little less than 30 feet high and 35 feet wide; for not merely has the rock to be removed at the top and sides, which is afterwards replaced by masonry, but it is occasionally excavated for an inverted arch, which is placed wherever it is necessary.

The temperature is, as nearly as possible, the same at the roof of the gallery as it is on the floor; for jets of compressed air are let off above. The work of the masons would otherwise be unendurable.

There was a difference then of 18° between the temperature at the mouth and at the end of the finished work. In winter this amount would be trebled or quadrupled. How much of the increase is due to the lights, men, and horses, and how much to the natural temperature of the rock? If the heat increased in the tunnel,