These stoves can be obtained at any ironmonger’s or stove maker’s. A good form is that made by the London Warming and Ventilating Co., 14 Great Winchester Street, London, and is called the “Gurney” stove (Fig. 42). This is circular or cylindrical in form, with a dome top, and the gills, which are perpendicular, extend around the stove. A novel feature with this stove is that it is provided with a water-pan or trough carried round the base of the gills; when this pan is charged, the lower ends of the gills are immersed, and the heat that is conducted there causes the water to slowly evaporate. The advantage of a vaporising pan is this: before being warmed by an ordinary stove, fresh air holds a certain and proper amount of moisture, but as it becomes heated by such a stove the temperature is raised without proportionately increasing the moisture, and this is apt to make it unpleasantly dry, particularly to those suffering from asthma or any bronchial affection. The reverse is the case when the air becomes heated naturally (except when the wind is in the east); the proper proportion of moisture increases as the temperature rises; for instance, the atmosphere at 80° F. would contain about four times as much moisture as when at 32° F. The principle of the Gurney stove is such that the _natural_ degree of moisture is always maintained in the heated air. The greater proportion of modern close fire-stoves and furnaces have gills applied in some form or other. It might be mentioned that 13 Gurney stoves have effectually coped with the problem “How to heat St. Paul’s.” [Illustration: 42. Gurney Stove. 43. Convoluted Stove.] Another good form is “Constantine’s Convoluted Stove” (J. Constantine and Son, 23 Oxford Street, Manchester), Fig. 43. Instead of solid gills, there are a series of perpendicular convolutions which double the heating surface, and the makers’ claim to greater efficiency is no doubt correct. This stove, however, should be classed with hot-air furnaces, as it is not made in small sizes for direct heating; but for warming large buildings, churches, &c., for heating laundry drying-rooms, Turkish baths, &c., it is to be highly recommended.