In regard to the materials which it will be most advantageous to employ in the construction of Fire-places, so much light has, I flatter myself, already been thrown on the subject we are investigating, and the principles adopted have been established on such clear and obvious facts, that no great difficulty will attend the determination of that point.--As the object in view is to bring radiant heat into the room, it is clear that that material is best for the construction of a Fire-place which reflects the most, or which ABSORBS THE LEAST of it; for that heat which is ABSORBED cannot be REFLECTED--Now as bodies which absorb radiant heat are necessarily heated in consequence of that absorption, to discover which of the various materials that can be employed for constructing Fire-places are best adapted for that purpose, we have only to find out by an experiment, very easy to be made, what bodies acquire LEAST HEAT when exposed to the direct rays of a clear fire;--for those which are least heated, evidently absorb the least, and consequently reflect the most radiant heat. And hence it appears that iron, and, in general, metals of all kinds, which are well known to GROW VERY HOT when exposed to the rays projected by burning fuel, are to be reckoned among the VERY WORST materials that it is possible to employ in the construction of Fire-places. The best materials I have hitherto been able to discover are fire-stone, and common bricks and mortar. Both these materials are, fortunately, very cheap; and as to their comparative merits, I hardly know to which of them the preference ought to be given. When bricks are used they should be covered with a thin coating of plaster, which, when it is become perfectly dry, should be white-washed. The fire-stone should likewise be white washed, when that is used; and every part of the Fire-place, which is not exposed to being soiled and made black by the smoke, should be kept as white and clean as possible. As WHITE reflects more heat, as well as more light than any other colour, it ought always to be preferred for the inside of a Chimney Fire-place, and BLACK, which reflects neither light nor heat should be most avoided. I am well aware how much the opinion I have have ventured to give, respecting the unfitness of iron and other metals to be employed in the construction of open Fire-places, differs from the opinion generally received upon that subject;--and I even know that the very reason which, according to my ideas of the matter, renders them totally unfit for the purpose, is commonly assigned for making use of them, namely, that they soon grow very hot. But I would beg leave to ask what advantage is derived from heating them?