The plan proposed by Drs. Drysdale and Hayward of Liverpool is similar in principle:—Fresh air is warmed by a coil of hot-water pipes in the basement, and is admitted into the staircase and landings, when it is supplied to the different rooms by openings provided with valves. From the rooms, special outlets converge to a foul-air chamber under the roof. This is connected with a shaft leading from the kitchen-fire, the latter, therefore, acting as an extraction furnace. =Lighted Gas= may be employed to produce a current for ventilating purposes, as well as fire or hot-water. =Sunlight and Benham’s Ventilating Gas-burners=, have already been mentioned in this connection (page 149). They are extremely valuable means of ventilation, producing powerful currents of air from all quarters of the room unless they are specially enclosed. In theatres and similar buildings the =Chandeliers= may be made to extract vitiated air. Where a number of chandeliers exist, they may be connected by tubes with a main shaft, and all made to contribute to the same object. According to the experiments of General Morin, the discharge of 1,000 cubic feet of air is produced by the combustion of one cubic foot of gas. Various forms of gas-stoves are now sold, which act as ventilators as well as sources of heat. Among these is =George’s Calorigen Stove= (Fig. 17). It can be obtained in various forms suitable for burning coal-gas, or coal, or oil. Within its outer case is contained a special iron tube, which communicates at its lower end with the outer air, and opens at its upper end into the room. The heat generated in the stove warms the air in the spiral tube, which accordingly ascends into the room. The ascent of warm air causes a draught from below, and the consequence is, that so long as the combustion is going on, a current of warm air continues to ascend into the room. The products of combustion are carried out of the room by the pipe =F=. This stove is free from most of the objections appertaining to gas-stoves; it can be fixed into an ordinary fire-place, and made to keep the temperature of a room uniform. [Illustration: FIG 17. GEORGE’S CALORIGEN STOVE. =A=—The interior of the room. =B=—Exterior of building. =C=—Wall. =D=—The Calorigen. =E=—A cylinder. =FF=—Pipes communicating with stove and cylinder to supply air for combustion, and to carry off the products of combustion. =G=—Pipe for passage of fresh cold air to Calorigen. Can be carried above the floor between the joists, as may be more convenient. =H=—Outlet for air into the apartment after being made warm.] =Bond’s Euthermic Stove= is similarly constructed to the above, but is open below so that the air needed for the gas combustion is drawn from the interior of the room, and the continuous change of air is thus favoured.