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.

Yes; but the term affinity is objectionable in this case, because, as
that word is used to express a chemical attraction (which can be
destroyed only by decomposition), it cannot be applicable to the slight
and transient union that takes place between free caloric and the bodies
through which it passes; an union which is so weak, that it constantly
yields to the tendency which caloric has to an equilibrium. Now you
clearly understand, that the passage of caloric, through bodies that are
good conductors, is much more rapid than through those that are bad
conductors, and that the former both give and receive it more quickly,
and therefore, in a given time, more abundantly, than bad conductors,
which makes them feel either hotter or colder, though they may be, in
fact, both of the same temperature.

CAROLINE.

Yes, I understand it now; the table, and the book lying upon it, being
really of the same temperature, would each receive, in the same space of
time, the same quantity of heat from my hand, were their conducting
powers equal; but as the table is the best conductor of the two, it will
absorb the heat from my hand more rapidly, and consequently produce a
stronger sensation of cold than the book.

MRS. B.

Very well, my dear; and observe, likewise, that if you were to heat the
table and the book an equal number of degrees above the temperatur