ce 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.

Yes; and it is the facility with which metals conduct caloric that made
you suppose that a silver pot radiated more caloric than an earthen one.
The silver pot is in fact hotter to the hand when in contact with it;
but it is because its conducting power more than counterbalances its
deficiency in regard to radiation.

We have observed that the most dense bodies are in general the best
conductors; and metals, you know, are of that class. Porous bodies, such
as the earths and wood, are worse conductors, chiefly, I believe, on
account of their pores being filled with air; for air is a remarkably
bad conductor.

CAROLINE.

It is a very fo