windows, the layer of air between the two windows preventing, to a very considerable extent, the cooling of the air inside the room. It is not advisable to have double panes of glass in the same sash, as the moisture between them will render them more or less opaque in certain states of the weather. With double windows, air may be admitted by opening the outer one at the bottom and the inner one at the top. Where French casement windows are used, as they sometimes are unadvisedly in this climate, ventilation may be provided by having a louvred opening above the casements of the window, or by making a glass pane, or panes, capable of being swung forward on the lower edge. Lastly, Cooper's ventilator is largely used for windows, and also in the glass panes over street doors. It consists of a circular disc of glass, with five holes in it, placed in front of a pane of glass with five similar holes, and working on an ivory pivot at its centre. It can be moved so that the holes in it are opposite to those in the window pane, when air will, of course, come in; or, so that they are opposite to the places between the holes in the panes, when the air will be prevented from entering. It is obvious that the air is not admitted in an upward direction, but the disadvantage of this is partly counter-balanced by the fact that it is admitted in five small streams, and not in one large one, so that there is less probability of a draught.

The air may also be admitted through apertures made in the walls or doors. The simplest way to do this is to make a hole through the wall, and fasten a piece of board in front of it in a sloping manner, so as to

give the air an upward direction. It is better to put "cheeks," as they are called, on the sides, for they serve not only to attach the sloping board to the wall, but to prevent the air from falling out sideways into the room. This ventilator may be hidden by hanging a picture in front of it, and will cause no draught. I may state here that it is better, in a large room, to have two or more small ventilators of any kind whatever than one large one, and that no single inlet opening should be larger than a square foot. Openings of half that size are preferable. It is calculated that there should be 24 square inches of opening per head, so that a square foot would be sufficient for six persons. In such an opening as has been described, wooden or glass louvres may be placed. The same end may be attained by making one of the upper panels of a door to open forwards with hinges to a certain distance; or, even in some instances, by fixing it in this position. An obvious disadvantage, and one which always has to be considered in making openings through walls and doors, is that conversation which goes on in the room can be heard in the passage outside. Sherringham's valve is a modification of this plan, and can be fitted either into an outer wall or into one between the room and the passage or hall. It consists of a metal box to fit into the hole in the wall, with a heavy metal flap, which can swing forwards, and is exactly balanced by a weight at the end of a string passing over a pulley, weight acting as a handle, by means of which the ventilator can be opened or shut or kept at any desired position. What has been said before applies to these

the

ventilators. They should not be placed too near the ceiling, and this is the mistake that is generally made in fixing them. Stevens's drawer ventilator may also be mentioned here. The name almost describes it. It resembles a drawer, which is pulled out of the wall for a certain distance, and allows air to come into the room vertically in several streams between metal plates placed inside the drawer. Jennings's "Inlet," which is in use in the barracks, consists of an opening through an outer wall, into a chamber in which dust, &c., is deposited, and thence between louvres into the room. Here I may mention that it is sometimes advised to place perforated zinc or wire gauze outside the entrance of the ventilators, so as to prevent dust, &c., coming into the room. This is not advisable, as the apertures get clogged up, and the entrance of air is much impeded. It is better to have an iron grating which will prevent birds entering, and to employ other methods for preventing the entrance of dust, soot, &c. Where this is considered necessary, the plan of passing air through cotton wool, which must be frequently changed, may be adopted. Currall's ventilator for admitting air through the door is sometimes useful. It resembles his window ventilator almost exactly; a long slit is cut through the door, a perforated metal plate placed outside, and a flat plate fixed parallel to the door inside and in front of the slit, thus giving the air as it comes into the room an upward direction. An admirable plan for the admission of air into rooms is by means of vertical tubes-an old system, but one which has been brought into prominence of late years by Mr. Tobin.

A horizontal aperture is made in the wall into the outer air just above the floor, and then a vertical pipe carried against the wall to a height of from five to six feet. The cold air is thus made to ascend like a fountain into the room. It does so in a compact column, which only perceptibly spreads after it has got some height above the mouth of the tube. It then mixes with the warm air at the top of the room, producing no draught at all. In spite of the vertical height through which the air has to pass before it emerges into the room, a considerable amount of soot and dust of various kinds is brought in by it. This may be obviated by placing a little cotton wool in the interior of the tube. This, however, although a very efficient plan, has the serious disadvantage of impeding the current of air. A better one is that patented by the Sanitary Engineering and Ventilating Company; a tray containing water is placed in the horizontal aperture in the wall, the entering air being deflected on to the surface of the water by metal plates. The greater part of the dust is thus arrested by the water, which can be changed as often as necessary. In warm weather ice may be placed in the trays. Another plan is to place in a vertical tube a long muslin bag with the pointed end upwards, and kept in shape by wire rings. This provides a large filtering area, and offers very little resistance to the passage of air. The bag may be taken out and cleansed from time to time. Several contrivances have been devised for the admission of air close to the floor, just behind a perforated skirting board. Among these are Ellison's conical ventilator, mentioned in the last chapter, and Stevens's skirt

ing board ventilator, in which metal cups are placed in front of the inlet openings, and so distribute the air that no draught is felt. I think however, that it is only advisable to admit warmed air at a low level into rooms, but there is no reason why such openings should not be made high up in the rooms-behind cornices, for example. Prichett's paving, made of agricultural pipes, may also be used for making walls and partitions, and is obviously applicable for ventilating purposes, whether used as inlet or outlet.

We now come to speak of exit shafts and valves. The first and most important of these is the chimney, about which I have already spoken. I need only add here that it is advisable to do without the use of cowls upon chimneys wherever it is possible. If the chimney can be made high enough it will not require a cowl, and if it cannot, a simple conical cap is generally sufficient to prevent down draughts. There is no doubt, however, that Boyle's fixed chimney cowl for preventing down draught not only does so, but produces an up draught in the chimney when the wind blows down upon it, as can be readily shown by an experiment with a model. A small piece of wool is made to ascend in a glass tube by blowing vertically down upon the fixed model cowl placed upon the top of it. Of revolving cowls for chimneys, the common lobster-backed cowl is probably the best. Of the many cowls which have been invented with the object of increasing the up draught in exit shafts of various kinds, some are fixed, as Boyle's, Buchan's, Stevens's, and Lloyd's, and some revolving, as Scott, Adie, and Co's.,