at a loss to conceive how the ether can pass to the state of vapour
without an addition of caloric. Does it not contain more caloric in a
state of vapour, than in a state of liquidity?

MRS. B.

It certainly does; for though it is the pressure of the atmosphere which
condenses it into a liquid, it is by forcing out the caloric that
belongs to it when in an aeriform state.

EMILY.

You have, therefore, two difficulties to explain, Mrs. B. --First, from
whence the ether obtains the caloric necessary to convert it into vapour
when it is relieved from the pressure of the atmosphere; and, secondly,
what is the reason that the water, in which the bottle of ether stands,
is frozen?

CAROLINE.

Now, I think, I can answer both these questions. The ether obtains the
addition of caloric required, from the water in the glass; and the loss
of caloric, which the latter sustains, is the occasion of its freezing.

MRS. B.

You are perfectly right; and if you look at the thermometer which I have
placed in the water, whilst I am working the pump, you will see that
every time bubbles of vapour are produced, the mercury descends; which
proves that the heat of the water diminishes in proportion as the ether
boils.

EMILY.

This I understand now very well; but if the water freezes in consequence
of yielding its caloric to the ether, the equilibrium of heat must, in
this case, be totally destroyed. Yet you have told us, that the exchange
of caloric between two bodies of equal temperature, was always equal;
how, then, is it that the water, which was originally of the same
temperature as the ether, gives out caloric to it, till the water is
frozen, and the ether made to boil?

MRS. B.

I suspected that you would make these objections; and, in order to
remove them, I enclosed two thermometers in the air-pump; one which
stands in the glass of water, the other in the phial of ether; and you
may see that the equilibrium of temperature is not destroyed; for as the
thermometer descends in the water, that in the ether sinks in the same
manner; so that both thermometers indicate the same temperature, though
one of them is in a boiling, the other in a freezing liquid.

EMILY.

The ether, then, becomes colder as it boils? This is so contrary to
common experience, that I confess it astonishes me exceedingly.

CAROLINE.

It is, indeed, a most extraordinary circumstance. But pray, how do you
account for it?

MRS. B.

I cannot sati