are certain to get out of order some day or other. Whether they increase up draughts or not, there is no doubt that most of them prevent down draughts, and, like any other cover, prevent the entrance of rain.

Openings are sometimes made high up in the room into the chimney flue and protected by valves, the best known of which is Arnott's valve, which consists of a light metal flap, swinging inside a metal framework in such a way

FIG. 12.

that it can open

Arnott Valve.

towards the chimney flue, but not towards the room. Any pressure of air from the room towards the flue will, therefore, open it and allow the air to escape from the room into the flue. Pressure of air the other way will shut it. The disadvantages of this ventilator are that it makes an irregular noise, although this has been, to a considerable extent, obviated by the indiarubber padding with which it is now fitted. It also occasionally admits a little soot, and, of course, air at the same time, from the flue into the room. Boyle's exit ventilator, made by Messrs. Comyn, Ching and Co., is a modification of this. Instead of the light metal flaps, there are a number of small talc flaps. These make little

These air

noise unless there is much wind, when they flap to and fro noisily, but they are liable to be opened by a current of air in the chimney. It is obviously, it seems to me, at variance with sound sanitary principles to make openings from the interior of rooms into the chimney flues, and then to trust to valves for preventing the air of the flue from coming in. A far better plan is to have shafts placed by the side of the flues, and this, of course, is better done when the houses are built. The easiest and most satisfactory way of doing it, is by means of air and smoke flues combined, in which the air flues are moulded in the same piece of fireclay as the smoke flue itself. flues can be connected with the upper parts of the rooms, and up draughts will be inevitably caused, as the air in them will be considerably heated on account of its immediate contact with the outer side of the flue. Such shafts often become inlets when the flues are cold, and so it is advisable to use them especially with flues that are always hot-as, for instance, that of the kitchen chimney-and it is desirable, wherever it can be done, to connect the kitchen with a different air-shaft from the other rooms or it is possible that air from the kitchen may get into some of the other rooms of the house. Another exit ventilator is Kite's, in which there is no valve, but the shape of the air passage is relied on to prevent back draught.

I

Of exit ventilators not connected with the chimney flues, may mention Mackinnell's, which also provides an inlet for air as well, and which is very useful in little rooms, closets, &c., having no rooms over them. It consists of

two tubes, one inside the other, passing through the ceiling into the outer air. The inner one is longer than the outer one, and projects above it outside, and below it an inch or so into the room. At its lower end, a circular rim is attached horizontally, parallel to the ceiling. The outer air enters between these two tubes, and is deflected by the rim just mentioned along the ceiling, so that it does not fall straight into the room. The vitiated hot air passes out by the inner tube, the action of which is, of course, considerably increased if a gas burner or other light be placed beneath it. It is upon this principle that the lamps for lighting railway carriages are made, the reflector answering the purpose of the rim round the end of the inner tube, and the air to supply the lamp coming in between the reflector and the glass shade, while the products of combustion escape through the pipe leading from the middle of the reflector, and immediately over the flame. Of course Mackinnell's ventilator requires a cover to keep out the rain, and it is necessary, in fact, to have a double cover, so that the heated air which escapes by the inner tube shall not be carried back into the room by the entering air. Tossell's ventilator is a variety of this, with a cover by means of which the action of the wind is taken advantage of.

This brings us naturally to say a little about lighting. Candles, lamps, and gas help to render the air impure. It is calculated that two sperm candles, or one good oil lamp, render the air about as impure as one man does, whereas one gas burner will consume as much oxygen and give out

as much carbonic acid as five or six men, or even more. This is why it is commonly considered that gas is more injurious than lamps or candles, and so it is when the quantities of light are not compared, but with the same quantity of light, gas renders the air of a room less impure than either lamps or candles. If, in the dining room, instead of using five or six gas burners, as we too often do without any provision for the escape of the products of combustion, we used 40 or 50 sperm candles instead of 6 or 8, we should have a fairer comparison between gas and candles.

I have no time to enter into a discussion of the relative merits of various kinds of candles and lamps, but with regard to gas I would say that, considering the fact I have just stated, it is always advisable to provide a means of escape for the products of combustion immediately over the gas burners. By this, not only may these products be carried away, but, with a little contrivance, heated air may be drawn out of the room at the same time, and so an efficient exit shaft provided, in addition to the one found already in the chimney. Very simple contrivances will answer this purpose. A pipe, with a funnel-shaped end, starting from over the gas burner, and carried straight out into the open air, is all that is required in some instances, as in badly placed closets (an air inlet being provided). For large rooms, the sunlight ventilators are found to answer admirably. They should be provided with a glass shade, placed below them to intercept the glare, and to cut off a large portion of the heat. An elegant contrivance for dwelling-rooms is Benham's ventilating globe light.