If adopted it may be either on the hot-air or radiating plan, as in heating by means of furnaces. In the first method the fresh air is introduced into a chamber containing a coil of steam-pipes, and passes thence into the laconicum by a shaft or conduit, as in the case of air heated by a stove. In the second method, steam radiators--compact batteries of pipes--must be placed in recesses in the hot rooms, fresh air being introduced over them. The steam-pipes employed should be of the "small bore" type, about 5/8 inch internal diameter, and of wrought iron or copper. In order to ensure as far as possible against the danger of explosion, the system of pipes should be tested, when fixed, by severe hydraulic pressure. It is certainly a great advantage, in point of ease and economy, to be able to warm a building, drive machinery, and heat Turkish and Russian baths from one boiler, which can readily be done, very ordinary pressures of steam giving sufficient heat to keep the radiators of the requisite temperature. But the nature of the heating accomplished by means of steam-pipes is very inferior to that from large radiating surfaces of firebrick. The average temperatures of a public bath should range from about 110° in the shampooing rooms to 250°-260° in the hottest part of the laconicum, taking the readings of the thermometer at a level of 6 ft. 6 in. above floor-line. Between the entrance of the heated air and its point of furthest travel in the shampooing rooms, the bather should be able to select any temperature that may be most agreeable to him, and as many find by experience that a certain degree of heat is best suited to themselves, it shows attention to the _habitués_ of the bath, if the hot rooms are carefully maintained at the same uniform temperatures throughout the year. This may be 110°-120° in the shampooing rooms, 140° in the tepidarium, 180° in the calidarium, and 250° in the laconicum. These must be the maxima of the average temperatures of each room at 6 ft. 6 in. above the floor. In a pure atmosphere the highest temperatures are comfortable, but in a foul one they become insupportable.