Open Fire-places.
The manner in which rude nations kindle a fire in or near their huts, is one of the most wasteful arrangements in which fuel can be used. Houseless savages, because they know no better, and soldiers at bivouac, because they must make a virtue of necessity, kindle a fire in the open air, and place themselves near it, benefiting by that portion of the radiant heat which falls on their bodies; but all the rest of the heat is wastefully dissipated.
The next step of improvement is, to kindle a fire in a place more or less inclosed. Under this arrangement, not only will that part of the radiant heat which falls on the persons be available, but a portion of the remainder also, which, falling on the walls and warming them, is partially reflected; and moreover, heat combined with the smoke will be for a time retained in the place, and thus still further contribute to the warmth of the interior. By such an arrangement, nearly the whole of the heat evolved in the combustion is applied to use; but it is contaminated with the smoke from the fuel. The savages of North America place fires in the middle of the floor of their huts, and sit around in the smoke, of which the excess escapes by the one opening in the hut that serves as a chimney, window, and door. A few of the peasantry in the remote parts of Ireland and Scotland still place their fires in the middle of their floors, and leave for the escape of the smoke only a small opening in the roof, often not directly over the fire. In Italy and Spain, almost the only fires seen in sitting-rooms are large dishes of live charcoal, or braziers, placed in the middle, with the inmates sitting around, having to breathe the noxious carbonic acid gas which ascends from the fire and mixes with the air of the room: there is no chimney, and the windows and doors are the only ventilators. The method of warming with open fires in the middle of the room was adopted in some of the English Colleges, and some of the London Inns of Court, down to a comparatively modern period.
A step further in advance is to have a fire, not only in an inclosed space as a means of keeping in the heat, but with an aperture over it to act as a chimney or vent for the smoke. This is the form, under various modifications, adopted in most English houses; the fire being kindled in a kind of recess under a chimney. By degrees we have become accustomed to the adoption of a grate, which keeps the fuel at a certain height above the ground; but the principle involved is just the same. In olden times the fire used to be kindled on the hearth under a huge chimney, or on a very low grate; but the general course of modern improvement has tended to lessen the size of the chimney, and to raise the grate higher from the hearth.
The philosophy of a chimney is well explained by Dr. Arnott, in his Elements of Physics. He says: “Chimneys quicken the ascent of hot air, by keeping a long column of it together. A column of two feet high rises higher, or is pressed up with twice as much force as a column of one foot, and so, in proportion, for all other lengths; just as two or more corks strung together and immersed in water, tend upwards with proportionally more force than a single cork, or as a long spear of light wood, allowed to ascend perpendicularly from a great depth in water acquires a velocity which makes it dart above the surface, while a short piece under the same circumstances rises very slowly. In a chimney where one foot in height of the column of hot air is one ounce lighter than the same bulk of the external cold air, if the chimney be one hundred feet high, the air or smoke in it is propelled upwards with the force of one hundred ounces. In all cases, therefore, the draught, as it is called, of a chimney is proportioned to its length.”