In our last conversation, we began to examine the tendency of caloric to restore an equilibrium of temperature. This property, when once well understood, affords the explanation of a great variety of facts which appeared formerly unaccountable. You must observe, in the first place, that the effect of this tendency is gradually to bring all bodies that are in contact to the same temperature. Thus, the fire which burns in the grate, communicates its heat from one object to another, till every part of the room has an equal proportion of it. EMILY. And yet this book is not so cold as the table on which it lies, though both are at an equal distance from the fire, and actually in contact with each other, so that, according to your theory, they should be exactly of the same temperature. CAROLINE. And the hearth, which is much nearer the fire than the carpet, is certainly the colder of the two. MRS. B. If you ascertain the temperature of these several bodies by a thermometer (which is a much more accurate test than your feeling), you will find that it is exactly the same. CAROLINE. But if they are of the same temperature, why should the one feel colder than the other? MRS. B. The hearth and the table feel colder than the carpet or the book, because the latter are not such good _conductors of heat_ as the former. Caloric finds a more easy passage through marble and wood, than through leather and worsted; the two former will therefore absorb heat more rapidly from your hand, and consequently give it a stronger sensation of cold than the two latter, although they are all of them really of the same temperature. CAROLINE. So, then, the sensation I feel on touching a cold body, is in proportion to the rapidity with which my hand yields its heat to that body? MRS. B. Precisely; and, if you lay your hand successively on every object in the room, you will discover which are good, and which are bad conductors of heat, by the different degrees of cold you feel. But, in order to ascertain this point, it is necessary that the several substances should be of the same temperature, which will not be the case with those that are very near the fire, or those that are exposed to a current of cold air from a window or door. EMILY. But what is the reason that some bodies are better conductors of heat than others? MRS. B. This is a point not well ascertained. It has been conjectured that a certain union or adherence takes place between the caloric and the particles of the body through which it passes. If this adherence be strong, the body detains the heat, and parts with it slowly and reluctantly; if slight, it propagates it freely and rapidly. The conducting power of a body is therefore, inversely, as its tendency to unite with caloric. EMILY. That is to say, that the best conductors are those that have the least affinity for caloric. MRS. B.