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so that the air descends vertically, the velocity of the current entering through them should not exceed 1'6 feet per second; but when the air enters at the sides of the room at a consider able height the velocity niay be as high as 3’3 feet per second without causing inconvenience. The plan of ventilation by suc tion has been objected to as causing objectionable draughts of ail - when the doors are opened communicating with the exterior; but this sensation of draughts is got rid of when suitable pro portions are adopted, and when care is taken that the passages communicating with the exterior arc suitably warmed. The Ordinary chimneys of houses produce in many cases a sufficient abstraction of air even without a fire, from the ordinary differ ence of temperature between the internal and external air; and this ventilating power can easily be increased by intro ducing into the chimney a vertical pipe containing a few gas burners. An example of the application to a large building of the principles of ventilation described in the present paper is shown in Figs. 1 to 3, Plate 2, which represent the Public School in the Rue des Petits Hotels in Paris. This building contains an elementary school A A for 400 children, and a drawing school B for 270 pupils. The ventilation is at the rate of 350 cubic feet per hour per person, and the warming is effected by two heating stoves C C with vertical tubes. The warmed air is supplied to each story by three vertical channels D, which dis charge into a long wide passage E extending the whole length of the rooms, and into this passage external cold air can be admitted to regulate the temperature. The supply of air flows into the rooms horizontally near the ceilings, as shown by the arrows. The rooms of the drawing school B are open at night, and offer special difficulties in ventilation, from the large number of gas burners in use. The plan of abstracting the vitiated air close to the floor cannot be exclusively applied in this case, as it would cause the discomfort of pouring down air of 85° to 95° temperature upon the heads of the occupants. It is necessary therefore to allow the heated gases from the combustion of the lights to escape through the openings F in the ceiling, but at the same time fresh air is made to enter at the sides near the ceiling. In such cases, when the room has not attics above it through which the outlet openings in the ceilings can discharge, special flues are required to be made for this purpose, and these should be situated as far as possible from the points where the admission of fresh air takes place. By means of this plan of ventilation the temperature of the above rooms has been maintained until 10 o’clock at night at 71° at a height of 5 feet above the floor, and at an average of 75° near the ceiling ; but before this plan was adopted these temperatures were 80° and 91° respectively. The discharge openings should be made along both of the longer sides of the room, as shown at G G in Fig. 1, and should be as numerous as possible; and their total effective area should be such as to limit the velocity of the air passing through them to 2’3 feet per second. They communicate with descend ing passages H, converging below into a main discharge passage K leading to the bottom of the discharging shaft J. The chimney pipes I from the hot-air stoves C are made to pass up this shaft for assisting the draught, but a small fire L at the bottom of the shaft is also requisite. An example of the ventilation of a large meeting room is shown in Figs. 4 to 7, Plate 3, representing the Lecture Theatre of the Conservatoire des Arts et Metiers (in which the present meeting is held) and in which the ventilation arrangements have been carried out by the writer, and have been satisfactorily ■working for the last four years. The vitiated air is taken off through a large number of orifices made in the risers of the steps A A, Fig. 4, opening into the space B below the seats, which communicates by an outlet passage C, Fig. 5, with the discharging shaft D ; the requisite draught is maintained in the shaft D by means of a fire at the bottom, dampers being placed in the passage C to moderate the current of the air. The supply of fresh air is introduced from a mixing chamber E in the roof, and enters the lecture theatre through openings F F distributed over the surface of the ceiling. In such buildings the ventilation should provide an amount of 1000 cubic feet of air per hour for each person, and the area of openings for the abstraction of the vitiated air should be sufficient to prevent its velocity through the openings exceeding 2’3 to 2’6 feet per second, the openings being distributed as uniformly as possible over the whole of the steps A A. The velocity of the air in the outlet passage C should not exceed 3’9 feet per second ; and the velocity in the discharging shaft D should amount to 6’6 feet per second, in order to ensure the stability of the current. The inlet openings F F for supply of fresh air, when situated- in the ceiling, should have such an area as to allow the velocity not to exceed 1’6 feet per second; in this lecture theatre, where the total quantity of air admitted reaches 170 cubic feet per second, the area of openings slightly exceeds the above propor tion. When it is requisite in such places for the inJet openings to be at the sides, they should be situated on two opposite sides, and as high from the floor as practicable. As the ventilation of buildings like this lecture theatre is required to be in action only when they are occupied, whilst the ■warming is needed to be in operation previously to their occupation, it is necessary to have the means of warming them by special orifices, in addition to those -which supply the ventilation. For the purpose of warming, the large hot-air stove G is employed, Fig. 4, situated under the lower end of the- room; and the air necessary for combustion is supplied to it from the basement through the passage H. The fresh air to be heated is admitted through a separate passage I from the open court yard adjoining, and after being heated by the stove is delivered into the room through the four openings J J in the floor ; these are only opened during the preparatory warming of the lecture theatre while it is empty, and as soon as it is occupied they are closed. A constant supply of hot air is maintained to the two lobbies K K by the openings L L, and also by the openings M M to the laboratory N at the back of the lecture theatre; this prevents any objectionable draughts of cold air occurring when ever the intervening doors are open during the occupation of the theatre; and the doors being all made to open outwards, the tendency of the entering air is to close them. At the upper end of the lecture theatre a similar heating stove is provided, but of smaller size, for warming the main entrance staircase and vestibule at that end of the room. A portion of the hot air from the stove G is conveyed by the ascending pipe P to the mixing air chamber E in the roof; and in order to ensure its equal diffusion over all parts of the lecture theatre, the moutli of the hot-air passage Q is widened out to the full width of the air chamber E, as shown in the plan, Fig. 6 ; while a hood R is placed over the central inlet opening F, and screens S S are interposed at the two side open ings, in order to prevent an undue proportion of the fresh warm air from entering the lecture theatre through these three nearest openings. A branch from the hot-air passage Q to the two side openings T T, Fig. 7, ensures a proper supply of hot-air to each of these openings. A similar supply of hot-air is introduced at the other end of the roof by the passage V from the smalle heating stove at that end of the lecture theatre. The fresh cold air is admitted into the roof chamber E through the entrances U U, Figs. 4 and 7 ; and by the arrangement shown in the drawings of the hoods R and screens S at the ceiling apertures, the thorough mixing is ensured of the cold and the heated air previous to entering the lecture theatre, the orifices of the hot-air passages Q and V being situated in all cases close underneath those admitting the cold air. By means of the valves U IT the entrance of the cold air to the mixing chamber E is regulated according to the temperature desired in the mixed air introduced for ventilation; in winter this temperature should be about 3|° below that maintained in the lecture theatre, which should be about 68°. The ventilation of a large theatre is illustarted by Figs. 8 and 9, Plate 3, representing the Theatre Lyrique in Paris, in which the principle of the writer's plan of ventilation was adopted; but this was unfortunately only partially carried out in the details, so that the full advantage is not realised in the results. The number of seats in this theatre is 1470. For the ven tilation of the stage and its dependencies, special means have to be applied by an auxiliary discharge flue above the stage, intended for use when required to remove any large quantities of smoke from extensive illuminations. In the body of the house, where the maintenance of a constant ample ventilation is required, there should be a supply of fresh air of 1400 cubic feet per hour for esch person, with the means of increasing this in summer to 2000 cubic feet per hour. It is important for the supply of fresh air to be obtained from open spaces or gardens, if possible, or else by special shafts bringing the air from a point above the buildings, and far removed from the outlets of'
