As the smoke and vapour which ascend from burning fuel rise in consequence of their being rarefied by heat, and made lighter than the air of the surrounding atmosphere; and as the degree of their rarefaction, and consequently their tendency to rise, is in proportion to the intensity of their heat; and further, as they are hotter near the fire than at a greater distance from it, it is clear that the nearer the throat of a Chimney is to the fire, the stronger will be, what is commonly called, its DRAUGHT, and the less danger there will be of its smoking. But on the other hand, when the draught of a Chimney is very strong, and particularly when this strong draught is occasioned by the throat of the Chimney being very near the fire, it may so happen that the draught of air into the fire may become so strong, as to cause the fuel to be consumed too rapidly. There are likewise several other inconveniences which would attend the placing of the throat of a Chimney VERY NEAR the burning fuel. In introducing the improvements proposed, in Chimnies already built, there can be no question in regard to the height of the throat of the Chimney, for its place will be determined by the height of the mantle. It can hardly be made lower than the mantle; and it ought always to be brought down as nearly upon the level with the bottom of it as possible. If the Chimney is apt to smoke, it will sometimes be necessary either to lower the mantle or to diminish the height of the opening of the Fire-place, by throwing over a flat arch, or putting in a straight piece of stone from one side of it to the other, or, which will be still more simple and easy in practice, building a wall of bricks, supported by a flat bar of iron, immediately under the mantle. Nothing is so effectual to prevent Chimnies from smoking as diminishing the opening of the Fire-place in the manner here described, and lowering and diminishing the throat of the Chimney; and I have always found, except in the single instance already mentioned, that a perfect cure may be effected by THESE MEANS ALONE, even in the most desperate cases. It is true, that when the construction of the Chimney is very bad indeed, or its situation very unfavourable to the ascent of the smoke, and especially when both these disadvantages exist at the same time, it may sometimes be necessary to diminish the opening of the Fire-place, and particularly to lower it, and also to lower the throat of the Chimney, more than might be wished: but still I think this can produce no inconveniences to be compared with that greatest of all plagues, a smoking Chimney. The position of the throat of a Chimney being determined, the next points to be ascertained are its size and form, and the manner in which it ought to be connected with the Fire-place below, and with the open canal of the Chimney above.