Now you have explained it right; the flannel rather keeps in the heat, than keeps out the cold. Were the atmosphere of a higher temperature than our bodies, it would be equally efficacious in keeping their temperature at the same degree, as it would prevent the free access of the external heat, by the difficulty with which it conducts it. EMILY. This, I think, is very clear. Heat, whether external or internal, cannot easily penetrate flannel; therefore in cold weather it keeps us warm; and if the weather was hotter than our bodies, it would keep us cool. MRS. B. The most dense bodies are, generally speaking, the best conductors of heat; probably because the denser the body the greater are the number of points or particles that come in contact with caloric. At the common temperature of the atmosphere a piece of metal will feel much colder than a piece of wood, and the latter than a piece of woollen cloth; this again will feel colder than flannel; and down, which is one of the lightest, is at the same time one of the warmest bodies. CAROLINE. This is, I suppose, the reason that the plumage of birds preserves them so effectually from the influence of cold in winter? MRS. B. Yes; but though feathers in general are an excellent preservative against cold, down is a kind of plumage peculiar to aquatic birds, and covers their chest, which is the part most exposed to the water; for though the surface of the water is not of a lower temperature than the atmosphere, yet, as it is a better conductor of heat, it feels much colder, consequently the chest of the bird requires a warmer covering than any other part of its body. Besides, the breasts of aquatic birds are exposed to cold not only from the temperature of the water, but also from the velocity with which the breast of the bird strikes against it; and likewise from the rapid evaporation occasioned in that part by the air against which it strikes, after it has been moistened by dipping from time to time into the water. If you hold a finger of one hand motionless in a glass of water, and at the same time move a finger of the other hand swiftly through water of the same temperature, a different sensation will be soon perceived in the different fingers. Most animal substances, especially those which Providence has assigned as a covering for animals, such as fur, wool, hair, skin, &c. are bad conductors of heat, and are, on that account, such excellent preservatives against the inclemency of winter, that our warmest apparel is made of these materials. EMILY. Wood is, I dare say, not so good a conductor as metal, and it is for that reason, no doubt, that silver teapots have always wooden handles. MRS. B.