But to return to the subject more immediately under consideration. As we have seen what is necessary to the production or generation of radiant heat, it remains to determine how the greatest proportion of that generated and sent off from the fire in all directions may be made to enter the room, and assist in warming it. How as the rays which are thrown off from burning fuel have this property in common with light, that they generate heat only WHEN and WHERE they are stopped or absorbed, and also in being capable of being reflected WITHOUT GENERATING at the surfaces of various bodies, the knowledge of these properties will enable us to take measures, with the utmost certainty, for producing the effect required,--that is to say, for bringing as much radiant heat as possible into the room. This must be done, first, by causing as many as possible of the rays, as they are sent off from the fire in straight lines, to come DIRECTLY into the room; which can only be effected by bringing the fire as far forward as possible, and leaving the opening of the Fire-place as wide and as high as can be done without inconveniences; and secondly, by making the sides and back of the Fire-place of such form, and constructing them of such materials, as to cause the direct rays from the fire, which strike against them, to be sent into the room BY REFLECTION in the greatest abundance. Now it will be found, upon examination, that the best form for the vertical sides of a Fire-place, or the COVINGS, (as they are called,) is that of an upright plane, making an angle with the plane of the back of the Fire-place, of about 135 degrees.-- According to the present construction of Chimnies this angle is 90 degrees, or forms a right angle; but as in this case the two sides or covings of the Fire-place (AC, BD, Fig. 1.) are parallel to each other, it is evident that they are very ill contrived for throwing into the room by reflection the rays from the fire which fall on them. To have a clear and perfect idea of the alterations I propose in the forms of Fire-places, the reader need only observe, that, whereas the backs of Fire-places, as they are now commonly constructed, are as wide as the opening of the Fire-place in front, and the sides of it are of course perpendicular to it, and parallel to each other,--in the Fire-places I recommend, the back (i k, Fig. 3) is only about one-third of the width of the opening of the Fire-place in front (a,b), and consequently that the two sides of covings of the Fire-place (a i and b k), instead of being perpendicular to the back, are inclined to it at an angle of about 135 degrees; and in consequence of this position, instead of being parallel to each other, each of them presents an oblique front towards the opening of the Chimney, by means of which the rays which they reflect are thrown into the room. A bare inspection of the annexed drawings (Fig. 1. and Fig. 3.) will render this matter perfectly clear and intelligible.