When a fire is burning in the grate, all other openings in the room, except openings into the chimney, serve as inlets. If the room is insufficiently supplied with openings, a double current may be established in the chimney, with the result that occasional down-puffs of smoke occur. As a rule the chimney serves only as an outlet for impure air. It may by appropriate means be made to serve as an _inlet for pure and warmed air_, the heat which would otherwise escape up the chimney being utilised for this purpose. =Galton’s stove= is one of the best for this purpose. At the back of this stove is an air-chamber, communicating with the external air, and in which the fresh air is heated before it enters the room. On the back of the stove broad iron flanges are cast, in order to present as large a heating surface as possible. They project backwards into the air chamber; and their heating surface is aided by the iron smoke-flue, which passes through the air-chamber. The warmed fresh air enters the room by a louvred opening above the mantel-piece, or by an opening in each side of the chimney breast. By this stove one-third of the total heat of the fire is utilised, as against one-eighth in an ordinary fire-place. [Illustration: FIG. 16. Vertical Section through Two Rooms, showing—A. Currents of cold air with an ordinary fire; B. Direction of currents of warmed fresh air with a Galton’s Ventilating Stove.] Shorland’s Manchester and other stoves are constructed on the same principle as Galton’s. =The Ventilation of Mines= is effected by lighting a fire at the bottom of a shaft. The air for the combustion comes down another shaft (the intake shaft), or down another half of the same shaft separated by a partition. The consequence is that constant up and down currents of air are produced. The air from the intake shaft is made to traverse the galleries of the mines, its course being directed by partitions, before it is allowed to reach the fire and s be carried up out of the mine. In addition to, or instead of, an ordinary coal-fire, the power for extracting impure air may be obtained from =Hot Water or Steam Pipes=. There are various plans founded on this principle. When hot-water pipes are used for baths, etc., they may also be utilised for ventilation, in two ways:—1st. The hot-water pipe may be made to coil round the tube by which fresh air is admitted into a room, thus warming the air as it enters. 2nd. The hot-water pipe in its course upwards may be enclosed in a shaft, which opens into the external air above. The air in this shaft being heated, the impure air may be collected and removed from the different rooms by tubes connected with it. Thus, a hot-water apparatus, when well arranged and complete, may furnish pure warm air, and carry away impure air. The ventilation by this plan is found in practice to be somewhat irregular.