In a good bath, where there is a rapid and continuous flow of air, there will be comparatively little difference between the temperature at say 4 ft., 6 ft., and 8 ft. above the floor. In badly-ventilated rooms, where the air stagnates, there will be a considerable difference. And here we may note a serious objection to the heating of a bath by convection; for while the head may be in a high degree of heat the feet are in comparatively cool air, whereas, if possible, it should be just the reverse. In convected heat, this of course applies in its entirety, as where so-called radiant heat is employed the evil is not quite so marked. And here, too, we may note the admirable nature of the Roman system of heating, where the floors radiated the majority of the heat, and the walls a slightly less amount. The fresh air under the ancient system must have entered through the cooler rooms, and being drawn towards the _calidarium_ found its exit through the ceilings, at times by way of the regulating device mentioned by Vitruvius. Thus the ancient bather would not suffer the inconvenience that accrues to the bather in the modern hot-air bath, whose head, when he is standing upright, is in a considerably higher temperature than any other portion of his body. The temperature of a bath should not be regulated by the firing of the furnace. This should be regularly stoked, and kept at one uniform heat-giving condition. Bad firing and forced firing may crack the stove should it be of iron, and the air may be overheated. The temperature should be regulated by means of the hit-and-miss ventilators at the floor level. Fanlights between the various hot rooms, with screw-rod adjustment, serve as a means for regulating their relative temperatures. The heating power of furnaces must be studied. Having calculated the cubical contents of the rooms to be heated, and given the heating power of the stove or apparatus to be employed per cwt. of metal or superficial foot of radiating surface, we arrive at the necessary size. Messrs. Constantine give the following tables to show the heating power of the "Convoluted" stove. The figures give the requisite size of stove to raise the air to about the relative temperatures I have mentioned before, and with ordinary firing. Weight of Sq. ft. of Area capable metal. heating surface. of heating. --- --- --- cwt. sq. ft. cub. ft. 14 35 500 20 55 1,200 22 69 2,000 34 119 3,500 36 139 5,000 45 180 8,000 50 231 12,000 56 296 16,000