course, be a constant current downwards through the same or other shafts. The extent of ventilation in mines will depend on many circumstances, more especially on their depth, the number of shafts, the degree of communication between the different galleries, and also on the state of the wind at the surface. The cooling effect of high winds is very perceptible even at the bottom of shallow mines, and it appears that the currents of air in the very deepest mines are considerably influenced by their force and direction.
Though these currents in the shafts and more open galleries are considerable, it is still true, that in the great majority of the galleries no current, or one that is very slight, is perceptible; and that in all such galleries as communicate only by one extremity with a shaft, or with other levels by a wins at some distance from their inner extremity, (both of which kinds constitute the greater number of the working galleries,) there is no current whatever, and, in fact, no possibility of there being one. Many of these galleries are several hundred feet in length, with no other outlet but their extremity at the shaft. A sufficient proof of the general stillness of the air in mines, is afforded by the fact of lanterns being unknown in them; and during all my visits to these gloomy regions, I never saw the candle extinguished by a current of air, more than once or twice.
State of the air in mines.─The preceding details sufficiently point out the high temperature and great humidity of the air in mines. Many causes combine to render it also very impure, but particularly the following:─1st, the mechanical admixture of particles
