The temperature of the interior, about one-third up, is 450°, and at the top 213° F. The expansion during the week is very considerable from the accumulation of heat, and the interior of the tower is maintained at summer temperature by the radiation of the heat from the sides of the chimney.

Fire-grate. The most important part of the fire-place is the support for the fuel; it is generally constructed of iron bars, which admit air to the fuel, and is called the grate. The spaces between the bars of the grate should be wide enough to allow the ash to fall through, and at the same time sufficiently contracted to support the fuel. In many stoves and boiler fires no other entrance to the chimney is afforded except through the bars, and their shape as well as the distance between them, exert considerable influence upon the draught. The bars should be wedge-shaped, the wide side of the wedge being placed uppermost in the grate, and the total area for the admission of air between them should be, with reference to the diameter of the chimney, in the ratio of 1:4. As, however, a great part of the open grate surface is necessarily clogged with fuel while the process of combustion is going on, and some fuels offer much more impediment to the draught than others, no data generally applicable for the construction of grates, with reference to the relative areas of open grate surface and chimney vent can be given, although as a near approach to the ratio above stated, the practical rule is to leave an open grate surface equal in dimensions to the diameter of the flue. The greater the heating power of the fuel, the wider may be the grate, and vice versa. No grate is absolutely requisite when wood is used, the necessary air being admitted by holes in the door. The shape of the grate is of less importance; but when it aids the uniform sinking of the fuel, and is deepened or basket-shaped, it may materially assist the process of combustion. A very superior form of grate for large boiler fires will be described below, in connection with the consumption of smoke.

Methods of Heating Apartments and Dwellings.—In order thoroughly to understand the principles of applying heat, it is necessary to remember that the heat evolved from fuel is disseminated to surrounding bodies in two ways, by radiation and by immediate contact. Peclet has examined these points, with the aid of a very ingenious apparatus. He surrounded fuel, contained in a round wire basket, with a ring-shaped vessel, in such a manner that the quantity of water contained in the latter could only be heated by

radiation from the surface of the globular basket. By comparing the size of the radiating surface with the quantity and the temperature of the heated water, it was found that the radiated heat from wood was th, from wood charcoal, from coal about as much, and from peat and peat charcoalth of the whole amount of heat evolved. As a general result, the combustibles which burnt with the least flame yielded the most radiant heat. The radiant heat is therefore nearly always the smaller quantity, and on that account, the arrangements in which it alone is employed, are not economical for heating the air of dwellings.

Open Fireplace. The open fire-place, or hearth, is the most ancient mode of heating dwellings, and although it only affords radiant heat to the room, is still very generally employed in France and England. The fire-basket, or grate, is placed immediately below the chimney, which is widened into a recess to receive it; the fire thus burns unenclosed in the room, whence it draws the necessary air for the combustion of the fuel; the air becomes heated and passes off with the smoke into the chimney, without parting with any portion of its heat to the atmosphere of the room. It is almost impossible to regulate the quantity of air supplied to an open fire-place, and a considerable portion of the warmed air of the room is uselessly carried off by the draught. Thus the only way in which the fire can warm the air is by radiation. All the improvements made by Rumford and others upon open grates, tend to facilitate radiation towards the room, to make use of the escaping air as much as possible without injuring the draught, and lastly, to regulate the draught. The grate is frequently brought forward from the wall of the chimney, and the sides of the recess are so constructed that their inner surface, acting like the reflector of a lamp, shall collect the rays of heat and reflect them into the room; the size of the recess is sometimes lessened and fitted with dampers to prevent loss of heat, which, however, must always be very considerable in every open fire-place.

Numerous contrivances have at different times been invented for economizing the heat of the smoke and gases, which, in the ordinary arrangement of the open fire-place, pass directly into the chimney without parting with any portion of their heat. One such is shown in Figs. 90 and 91, adapted to a coal fire. The products of combustion here ascend through an iron pipe, which may be lengthened by bends to increase the heating surface.

This pipe is placed in a cavity of the wall above the mantel,

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which is connected at the lower extremity with a channel which communicates with the external air. Fresh air is thus warmed by contact with the pipe conveying the smoke and heated gases, and delivered into the room through a grating in connection with the upper part of the cavity. The objections to all such arrangements consist in the difficulty of cleaning the pipes, and the danger of mixing smoke with the fresh air from imperfection in the joints.

A stove fire-place, which combines the advantages of the open grate with those of the close stove, has been invented by Desarnod. It is constructed of plate-iron, and stands forward and isolated in the room, an iron plate being fixed at the back, through a slit in which the smoke passes to a series of pipes, which it traverses before being carried to the chimney. The room is then warmed, not only by radiation, but also by the immediate contact of the air of the room

with the heated iron plate and the pipe in which the smoke circulates. Desarnod's stove fire-place is very similar in principle to that described below.

The numerous advantages of an open fire-place are so highly valued by the inhabitants of this country, whose ideas of comfort and sociability are intimately connected with the fire-side, that it is not likely that other modes of heating rooms or dwellings will ever entirely supersede, this old-established plan of obtaining the necessary amount of warmth. The open fire-place and chimney afford the simplest possible means of creating a thorough circulation of air throughout the inhabited room, with which it is impossible to dispense without injury to health, and which is entirely absent in those arrangements on the continent, where the fuel is introduced into the stove and supplied with the requisite amount of air from without. The ventilation of the rooms is then entirely dependent upon crevices in windows and doors, and as these are avoided as much as possible in the construction of the houses, double windows and double doors being frequently employed, the air becomes vitiated in a very short time, especially where many persons are present, and the sallow complexions and stove-dried appearance of the occupants of such dwelling-rooms is one of the visible signs of their injurious tendency.

The ordinary arrangement of the fire-places in our dwelling-houses at present, however, is very defective. There is always a considerable loss of heat, the very unequal temperature diffused through the different parts of a room being exclusively derived from the radiant heat of an open fire. The only supply of air to the fuel is furnished by the crevices in doors, windows, or floors; and persons sitting by the fire, invariably experience the unpleasant sensation of excessive heat on the side exposed to it, while the other is cooled to an equally disagreeable extent by cold air rushing in from these different sources to maintain the combustion of the fuel. Another objection to open fireplaces and chimneys, is the downward draught frequently occasioned in neighbouring chimneys not in use, by large powerful fires in other rooms of the same building, which are not supplied from other sources with sufficient air for the consumption of the fuel. Foul air, carrying with it particles of soot, is thus disseminated through the rooms, to the detriment of health and cleanliness.

The late Mr. Sylvester made several improvements upon the open fire-hearth, which have been adopted with great advantage in

many public offices as well as in private houses. In Sylvester's stoves the fuel is placed upon a grate, the bars of which are on a level with the floor of the room, and air is supplied to the ashpit below by a series of passages which pass under a hearth composed either of separate bars of iron, arranged in a radiating manner in front of the grate, or of ornamental fire-tiles. The radiant and conducted heat from the fire is thus made to warm the hearth and the air passing below it, while the low position of the fire, and the inclination which may be given to the back and sides of the grate, tend to disseminate the heat much more effectually through the room than is usual in the ordinary arrangement of the fire-place. The sides and top of these stoves are constructed of double casings of iron, and in the sides a series of vertical plates are enclosed, parallel with the front facing, which collect, by conduction, a great portion of the heat generated from the fire, the mass of metal of which these are composed being so proportioned to the fuel consumed, that the air can never rise above the temperature of 212° F. under any circumstances. The sides and top of the stove are thus converted into a hot chamber, offering an extensive surface of heated metal; at the bottom, by an opening in the ornamental part, the air is allowed to enter, and rises as it becomes warmed, traversing in its ascent the different compartments formed by the hot parallel plates, and is allowed to escape at the top by some similar opening into the room. A current of air is thus constantly traversing the hollow