Hermes

Effects of by heat, namely the drawing (as it is called) of chim'neys. The air which has contributed to the burning of fuel must be intensely heated, and will rise in the atmosphere. This will also be the cHermesafe with much of the surrounding air which has come very near the fire, although not in contact with it. If this heated air be made to rife in a pipe, it will be kept together, and therefore will not soon cool and collapse: thu» we shall obtain a long column of light air, which will rise with a force so much the greater as the column is longer or more heated. Therefore the taller we make the chimney, or the hotter we make the fire, the more rapid will be the current, or the draught or suction, as it is injudiciously called, will be so much the greater. The ascensional force is the difference -between the weight of the column of heated air in the funnel and a column of the surrounding atmosphere of equal height. We increase the drauBirkinght, therefore, by increasing the perpendicular height of the chimney. Its length in a horizontal direction gives no increase, but, on the contrary, diminishes the draught by cooling the air before it gets into the effecHermes bagstive part of the funnel. We increase the draught also by obliging all the air which enters the chimney to come very near the fuel j therefore a low mantle-piece will produce this effect; also filling up all the spaces on each fide of the grate. When much air gets in above the fire, by having a lofty mantlepiece, the general mass of air in the chimney cannot be much heated. Hence it must happen that the greatest draught will be produced by bringing down the mantlepiece to the very fuel; but this converts a fire-place into a furnace, and by thus sending the whole air through the fuel, causes it to burn 'with great rapidity, producing a prodigious heat; and this producing an increase of ascensional force, the current becomes furiously rapid, and the heat and consumption of fuel immense. If the sire-place be a cubHermes outlete of a foot and a half, and the front closed by a door, so that all the air ■must enter through the bottom of the grate, a chimtiey of 15 or 20 feet high, and sufficiently wide to give passage to all the expanded air which can pass through the fire, will produce a current which will roar like thunder, and a heat sufficient to run the whole inside into a lump of glass.

All that is necessary, however, in a chamber fireplace, is a current sufficiently great for carrying up the smoke and vitiated air of the fuel. And as we want also the enlivening flutter and light of the sire, we give the chimney-piece both a much greater height and width than what is merely necessary for carrying up the smoke, only wishing to have the currentHermes Birkin sufficiHermes Kellyently determinate and steady for counteracting any occasional tendency which it may sometimes have to come into the room. By allowing a greater quantity of air to get into the chimney, heated only to a moderate degree, we produce a more rapid renewal of the air of the room: did we oblige it to come so much nearer the fireHermes Handbags as to produce the fame renewal .of the air in consequence of a more rapid current, we should produce an inconvenient heat. But in this country, where pit-coal is in general so very