supplying a light exterior to the Calidarium when the bath is used in the evening. Following this description, it will be seen that the Calidarium or Sudatorium is simply a closed chamber, with an area of sixty-five superficial feet, and containing seven hundred and fifteen cubic feet of atmospheric air, the actual measurements being ten feet long by six feet and a half wide, and eleven feet high; this chamber being provided with sufficient means of ventilation through the agency of the imperfectly-fitting doors, and also the occasional opening of the doors on one side, and the four holes, already described as existing in the exterior wall, on the other; and also, supposing the doors to be more closely shut, between an ingoing current of cold air through the two lower holes, and an outgoing current of hot air through the upper holes. Ten persons can take the bath without discomfort, and without being overcrowded in Mr. Witt's thermæ; I have myself formed one of nine, but with six or seven the space is more than ample. Let me now turn to the means of heating the Calidarium. In the exterior wall, near its bottom, and opening on the lead flat, is a furnace of the commonest possible construction, and capable, from its free draught, of burning the commonest combustible material--such as inferior coal, coal screenings, coke, cinders, and sawdust. This furnace, encased in brickwork, is carried obliquely for a distance of four or five feet into the Calidarium; and its flue, following the angle of the floor, makes the circuit of the apartment. The flue next ascends perpendicularly for a few feet, crosses the wall above the brickwork which encloses the furnace, and then makes its way up the angle of the room to the ceiling, where it escapes by means of a chimney. The flue, in its course around the room, is raised from the level of the floor, and separated from the wall by the breadth of a brick, and consequently presents a free surface on all sides for the radiation of heat. Its radiating surface is about one foot square, and its length thirty-five feet. The common temperature maintained in Mr. Witt's Calidarium is 130° to 140° of Fahrenheit. Mr. Witt tells me that he has had it as high as 180°; and I have myself been in it, in company with my friend Mr. Chadwick, at 150° of Fahrenheit.