better estimated if we consider the state of fireplaces in most European countries fifty or sixty years ago. 'The most polished nations of antiquity,' says Dr. Renwick, 'had no other means of providing for the issue of the smoke of their fires than by leaving openings in the roof. They indeed appear, in some instances, to have heated apartments by flues circulating beneath the floors, which must have terminated in a vertical funnel, thus forming an approximation to the chimney; but there appears to be no instance of the arrangement of an open hearth and vertical flue until late in the middle ages. Chimneys and fireplaces of the latter date are still to be seen in the kitchens and halls of baronial mansions; but the hearths were of great size, the arched openings wide and lofty, insomuch that they could be entered by persons standing upright, and admitted seats to be placed on each side of the fire. The latter, indeed, were the only places where the warmth of the fire could be enjoyed without exposure to the currents of cold air continually rushing in to join the ascending column in the chimney. Even when an increasing scarcity of fuel compelled less extravagant modes of applying it to be sought, the arched opening remained of a large size, the fireplace of a depth equal in extent to its front, and the walls were carried back perpendicularly to the latter. In England, where coal had come into almost universal use as a fuel, the grates in which it was burnt were almost exact cubes, and were lined with cast-iron on the sides and back. The evils of these fire-places may be recollected by all whose age reaches fifty; and they are remembered with feelings in which shuddering and scorching are strangely combined, but which are almost unknown, and scarcely to be imagined, by the present generation. Chimneys which did not smoke were the exception to the general rule; and the exposure of the surface of the body to cold currents generated the acute pains of rheumatism, while the frequent alternations of an increased and checked perspiration caused colds, to be followed, in regular course, by pulmonary complaints. In this state of things Rumford undertook to remedy the manifold evils of the open fireplace.'
Observing that the heat of a mass of blazing fuel in a grate consisted of two parts—that which radiated into the room, and served the purposes of warmth; and that which, by heating the column of air in the chimney, caused it to ascend, Rumford saw that an enormous saving could be effected by diminishing the size of the grate. Instead of a cubical mass of fuel, such as was generally used, he proposed to employ a grate of ordinarily broad front, but not deep backward, and with the sides not perpendicular to the front, but inclining. The effect of this was to limit the fire to the single function of warming the room by radiation from its front, while the mass of coal which had formerly been consumed without any benefit to the apartment was saved. In order, however, to prevent the smoking of the chimneys which would have arisen from this diminution of the burning mass, another change was necessary, and this was the narrowing the throat of the chimney, so as to allow no more air to pass through it than the precise quantity required to maintain the combustion. 'The immoderate size of the throats of chimneys,' says Rumford, 'is the great fault of their construction. It is this fault which ought always first to be attended to in every attempt which is made to improve them; for however perfect the construction of a fireplace may be in other respects, if the opening left for the passage of the smoke is larger than is necessary for that purpose,
