I have to mention next a very simple means by which air can be introduced into a room by means of the window, so as to go upwards, even in the coldest weather without anybody experiencing a draught. A piece of wood, about three inches high, which runs the whole width of the window, is placed underneath the lower sash, which is shut down upon it; this of course prevents the top and bottom sashes fitting in the centre of the window, and an opening is left, so that air comes in and goes upwards. It has a small disadvantage, and that is, that there is no provision for the exclusion of blacks, but that has been to a certain extent rectified by one of Mr. Tobin's plans. He does not put a block underneath the lower sash; he cuts little pieces out of the bottom piece of wood of the top sash, and the air comes in and goes straight up, and no one can see that the holes are there. You can even hold a candle in front of the window, and no effect whatever is shown upon the flame. Into these little holes he introduces a small box, and fills it with cotton wool, keeping the wool in its place by little threads passing from side to side. That wool filters the air so that no blacks can come in. You can also have some small lids fastened on to the top part of the bottom sash to turn over and cover the holes whenever you choose, so as to prevent air coming in at all. If cotton wool is used it must be changed pretty frequently, for it is astonishing how soon it gets dirty.

Louvre ventilators are made of slips of wood, glass, etc., very much like Venetian blinds - which latter make good ventilators if you open the top of the window, and turn the blind so that the laths slope upwards.

Windows have been constructed so that when the top sash is lowered it pulls down a contrivance made of louvres, but this is rather a complicated arrangement. Louvre ventilators, made of glass, are largely used, and can be put into a window instead of one of the panes. You can open or shut them, and put them at any angle you please. The disadvantage that they have is that the metal framework is liable to rust so that they will not work, but with care they do very well.

Windows which slope when they open are used sometimes, and they afford a very good means of letting a large volume of air into assembly rooms, etc., which are liable to be overcrowded.

In some cases, especially where French casement windows are used, Cooper's circular disc ventilator is fixed. It is entirely made of glass - a circular disc with five holes in it, corresponding with five holes in the pane. The disc can be turned so that the holes in it are or are not opposite to those in the window-pane, so that air can be admitted or not at pleasure. One advantage of this ventilator is that it has no metal framework, and so cannot get rusty.

In conclusion, I will mention the vertical shaft plan, which was re-introduced a short time ago into this country by Mr. Tobin. Its action depends upon the principle described just now; wherever you make an opening into the outer air, air will come in, by reason of the greater pressure outside, and if you admit air into a room through a vertical shaft, the air will rise up through the shaft and come into the room like a fountain, but no draught will he felt. One advantage of this plan is that you can filter the air in various ways, by passing it through cotton-wool, or you can pass the air over the Surface of water placed in the tube leading to the vertical shaft, deflecting the air on to the surface of the water by causing it to strike against sloping pieces of metal In that way the suspended particles in the air are driven, as it were, on to the surface of the water, and the air passes on into the vertical tube which rises up into the room. That is a very admirable contrivance, though not so simple as some of the methods I have before described. I should add that it is patented.

Now let us consider the ways in which foul air gets out of rooms. In the first place, a very large quantity of air passes out of all rooms by the chimney, whether there is a fire or not, provided that fresh air can come into the room somewhere else; Whenever the air outside is colder than the air inside, the air will go out through the chimney; that is partly due to the diminution of pressure, which causes an up-draught in the chimney whenever air is moving over it, which is nearly always the case. It has been thought by many that it would be advisable to have some means by which the air at the top of an apartment, which is always warmest, could be drawn off; and one of the earliest contrivances to effect this was Neil Arnott's valve, which is a valve placed in a box, opening into the chimney; it is a very light metal valve, which can only open towards the chimney, so that whenever the pressure of the air in the room is greater than that of the air in the chimney, it opens and allows air to escape from the room into the chimney, and when the contrary is the case it shuts, and so prevents the air in the chimney from coming into the room, and when it is not required it can be fastened by means of a string attached to it. The disadvantages of that valve are, that after a time it gets out of order, and doe3 not close so easily, and so a certain amount of air and blacks from the chimney get into the room; it also makes a clicking noise, which is unpleasant, especially in a bedroom. Yon can sleep if there is a clock in the room, because the ticking is regular, and you get accustomed to it, but it is extremely unpleasant and disturbing to have an irregular ticking or clicking. That valve was improved upon by Boyle, who, instead of employing a metal flap to be blown by the air towards the chimney, used a series of little pieces of talc, which acted in precisely the same way as Arnott's valve; but if you blow against these little flaps from behind with a sudden strong gust, the air catches underneath their edges, and opens instead of shutting them. A better plan than either of these is to have a separate shaft, side by side with the chimney, so that the air is warmed by contact with the flue, and an up-current is promoted in the shaft which communicates with each room, and so air is extracted without any possibility of blacks getting into the house.