The subject of heating: by hot water may be conveniently divided into two parts - low-pressure heating and high-pressure heating, which will be dealt with separately, as the arrangements of the various parts of the systems differ considerably. The low-pressure system has found by far the greatest favour in Great Britain, by reason of its greater safety ad efficiency. The pipes are, however, larger than in the high-pressure system, and therefore the latter may sometimes be preferable. If the apparatus has been once properly installed, it should require very little attention, and an ordinary domestic servant, without any special training, can easily attend to the small amount of stoking required. The apparatus in either case will consist of a hot-water boiler, heated by a fire, gas, or oil, aeeording to the magnitude of the work to be done, and a system of water-circulation pipes, either themselves giving off the heat, or connected with special groups of heating-surfaces known as radiators. Besides this, in the case of a low-pressure apparatus, a special feeding cistern and pipe will be required. in order that the whole of the system may be kept full of water. In the high-pressure system, such an arrangement is not necessary.

In comparison with heating by open grates or stoves, the systems of heating by water posses the following advantages:- There is only one central fire to be attended to, and this is usually placed in the basement, entirely out of sight, at a point close to the fuel-store. In this way all dirt and dust from the use of coal and the removal of ashes are kept out of the house proper, or relegated to a place where their presence is not so objectionable. As the fuel can be usually delivered close to the point where it is to be used, the annoyance and trouble caused by the filling of coal-scuttles, and the transport of coal through the living-rooms, are entirely avoided. The temperature of each room can be regulated to any desired degree, and ventilation can be effected quite as easily as by means of open fires. The radiating surfaces can be placed in the best possible position for giving the desired result, and can at the same time be made to counteract the evil effects of draughts produced by badly-fitting windows, etc. Equable warmth over a whole apartment can be obtained without difficulty. With the low-pressure system there is no danger to children, as they cannot possibly be seriously injured, even if they touch the radiating media, although, of course, it is preferable to protect these where very young children are constantly present. If the radiating surfaces are kept at a relatively low temperature, the passage of the incoming air over them will not deteriorate it. as may be the case where the air is passed over highly-heated surfaces, in contact with gases produced by burning fuel.

The position of radiators is a matter of some importance; they are usually placed in front of the windows, so that an upward current of warmed air may be produced, in the very place whence a cold draught usually proceeds . It is, however, preferable to form a special opening through the wall, directly under the window, and to place the radiator in a special case, through which the incoming air is taken. In this way. only warmed fresh air can enter the apartment, and the vitiated air must then be allowed to pass out by some specially-prepared openings. One of the objections to the use of radiators is that the current of warm air, ascending from the heating-surfaces, carries up with it particles of dust from the atmosphere, and from the floor of the room. After a time, this will cause a large black stain upon the wall. This is an additional reason for placing the radiators in front of the windows. In corridors and places of that kind, where such an arrangement is impossible, a shelf with a bracket at each end should be so arranged as to deflect the currents of heated air out from the wall.

One of the chief objections to hot-water warming:-apparatus, is that the appearance of the radiators and pipes is not cheerful; and, in Great Britain at any rate, the cheerfulness of an open fire, though accompanied with inequalities of warming, is preferred before the more equable temperature obtained by the use of radiators.

There is no reason, however, why a combined system of open fires and hot-water heating- should not be used. The flue of the fireplace might then be

1 as an outlet for the vitiated air, unless gas or oil is being burnt for the illumination of the room, in which case I consider it desirable to form the outlets close to the ceiling. There are many instances where a hot-water system of comparatively small size and little cost, might be installed in a house, for the purpose of heating the bedrooms, hall, and corridors, while open fires might be retained as a means of heating the sitting-rooms on the ground-floor. With a very small expenditure of fuel, the sleeping apartments might then be kept at a temperature of 55 degrees during the night; and the labour of stoking would be very little, as special boilers are now made which will burn for twelve hours without attention.