The acoustic and sanitary problems are here identical--to find a method of preventing an accumulation of foul and inelastic vapors around the breathing and listening congregation, and to give, instead, wholesome air to their lungs, while enabling their ears to hear. And since these poisonous and inelastic gases are specifically heavier than atmospheric air, and must fall to the floor by their own weight, the problem is reduced to providing a practicable way for their escape, and guarding it against counter-currents which might obstruct the passage. The introduction of warm air through openings in or near the floor will not readily produce uniformity of temperature within a room. The simplest experiment in proof of this is constantly made by multitudes of people, who, in crowded assemblies, find their heads surrounded by warm and moist vapors, reeking with offensive odors, while their feet are chilled, though near the “hot-air register.” A library, whose walls were 12 feet high, and whose floor--18 by 15--contained 270 square feet, was constantly warmed by a “Latrobe heater,” placed in the chimney at one end of the room. The pot holding the coal was raised one foot above the level of the floor, which was covered by a woollen carpet. Immediately under the library was a kitchen, whose temperature was kept at about 72° F. Three thermometers were placed thus: No. 1, standing on the carpet near the centre of the library floor; No. 2, three feet, and No. 3, six feet, above it. At the expiration of half an hour, No. 1 indicated 62°; No. 2, 66°; and No. 3, 72°. Numbers 1 and 3 were then placed side by side with No. 2, three feet above the floor. At the expiration of fifteen minutes, all three indicated the same temperature of 66°. The low temperature of the inferior stratum of air was certainly not due to that of the room beneath it, for that was above 70°. It was only the heavier, colder air of the room itself, and of adjacent apartments warmed in the same way, slightly affected by contact with the stratum of warmer air above it. Such slight differences of temperature in small apartments could not greatly affect the transmission of “the _pulse of sound_.” But in larger and loftier rooms, like churches and public halls, corresponding differences of temperature would, and do, produce air _strata_ widely different in density and elasticity, and occasion serious acoustic defects. But the acoustic requirement is not satisfied by uniformly elastic _air_ alone; for its _pulses_ are reflected, and unity--distinctness--of sound, is lost in echoes or reverberations, from windows, columns, floors, and ceilings.