of water often burst out, sometimes flooding a Whole mine. The ventilation, too, is most im portant, as the lives of all in tho pit depend npoa its perfection. The system of Bending fresh pure air through all tho labyrinth of passages is too complicated to be explained here, it is sufficient to say that a strong cur rent is created by a largo Can revolving with great rapidity, which expels the foul gases and brings the wholesome air down from the open world.