The thorough ventilation of our coal and other deep mines is a question of much importance, and is becoming more so every day, as our mining operations are extending very rapidly In older countries, especially England, where deep mining has been carried on for a great number of years, on a very extensive scale, it would naturally be inferred that the utmost perfection in ventilating agencies would have been readied long before this period, but such has not been the case It is only within the past two or three years that the greatest improvement yet suggested in ventilating mines has been carried out in that country This consists in the employment of positive machinery for the purpose, which has been erected at the Abercarn collieries It consists of a rotary fan driven by a small noncondensing steam engine ; and it has been constantly at work, day and night, for more than two years, without once being stopped for repairs The common method of ventilating fiery mines heretofore practiad, has been by a large fire kept burning at the bottom of an upshaft, at such a distance from the main shaft that the air rushing down the latter to feed the fire, passed through all the workings, and then escaped in a rarified column through the upshaft This method is rude and inefficient, affording no remedy for an increase of air, except by enlarging the fire, and it is rendered useless by being extinguished when an explosion takes place—just at the very time when a greater quantity of fresh air is most urgently required The rotary fan at the Abercarn colliery was put up by the ingenious James Nasmyth, the inventor of the steam hammer ; it is 13 feet in diameter, has eight vanes, made of plate iron, each 3 feet 6 inches wide, and 3 feet long, fitted on a horizontal shaft It is enclosed in a plate iron case, with large openings at the center, and trunks for discharging, something like our blowers for furnaces ; but it exhausts from the mine, thus causing the fresh air to rush down the main shaft, and pass through the workings to the upshaft The mine is 300 yards deep, has seven miles of railroad in it, and fourteen miles of working courses About 3,000 tuns of materials—coal, iron ore, and fir clay—are raised from it weekly The fan is driven at the rate of 60 revolutions per minute, and draws 45,000 ciic feet of air through the mine in that period This quantity supplies an abundance of air for the miners; their health has been greatly improved, and they can now labor during a greater number of hours daily When an explosion takes place in a coal mine, the greatest danger of immediate suffocation to the workmen, arises, not so much by inhaling carbonic acid gas, as some have supposed, as by the lungs becoming clogged by inhaling fine flaky soot, which generally saturates the atmosphere To avoid this danger, the miners who are'not burned, generally cover their mouths and noses with their handkerchiefs, and lie down, but unless they receive a supply of fresh air very soon, thsy must perish An explosion of some extent took place at the Abercarn colliery, since the above ventilating machinery was erected, but the flaky soot and foul air were abstracted, and the fresh air rushed in so rapidly that none of the miners lost their lives It is believed that but for the rapid and effective action of the ventilating fan on the occasion, every person in the mine would have perished The velocity of the fan can be augmented or diminished at pleasure ; and as the mine is very dangerous, this is necessary, in order to supply an increased quantity of fresh air on a sudden emergency Our mining companies would do well to pay munh attention to this subject