Messrs. Korting bros., of London, induced by the interest that has been directed to the separate ventilation of mines in which fire-damp is apt to form, have adopted for this purpose their jet ventilator. The instrument, which we illustrate in Fig. 1, has been, we understand, considerable simplified, and adapted for the special object in view. The ventilators are worked by compressed air, and are so arranged that, without stopping their action, the quantity of air they deliver can be rapidly increased or diminished. This ample power of control has been arranged for by the special wish of the mining authorities, who wish to regulate the ventilation according to the development of fire-damp or the greater or less number of men at work. Under circumstances of this kind the quantity of air taken into the mine can be changed instantly. The illustrations, Figs. 2, 3, and 4, show different modes of fixing the jet ventilator. In Fig. 2, it is arranged to blow the air forward; in Fig. 3, it is shown exhausting the air; and in Fig. 4, it is represented as exhausting and blowing simultaneously, the efficiency in each case being always the same. Any bends in the conduit affect the result to a very slight degree, and the ventilator may be used with advantage when the conduit is divided as in Fig. 4, in order to get the fresh air to different points. The ventilators are easily fixed to the air conduits. If they are to be connected to zinc air pipes, the pipe is simply slipped over the point, L. in Fig. 1, and if to wooden conduits the apparatus is simply put into them, and if no other support is required. Furthermore, they are so light that it suffices for one man to fix them or change their position. Messrs. Korting Bros. advance the following claims for this mode of ventilating mines: Certainty of action, no moving parts whatever, and, consequently, no need of lubrication; no need of attention. --_Mech. World_. * * * * * ON REMELTING OF CAST IRON.