example of latent heat, producing a change of form. At first it
converted a solid body into a liquid, and now it turns the liquid into
vapour!

MRS. B.

You see, my dear, how easily you have become acquainted with these
modifications of insensible heat, which at first appeared so
unintelligible. If, now, we were to reverse these changes, and condense
the vapour into water, and the water into ice, the latent heat would
re-appear entirely, in the form of free caloric.

EMILY.

Pray do let us see the effect of latent heat returning to its free
state.

MRS. B.

For the purpose of showing this, we need simply conduct the vapour
through this tube into this vessel of cold water, where it will part
with its latent heat and return to its liquid form.

EMILY.

How rapidly the steam heats the water!

MRS. B.

That is because it does not merely impart its free caloric to the water,
but likewise its latent heat. This method of heating liquids, has been
turned to advantage, in several economical establishments. The
steam-kitchens, which are getting into such general use, are upon the
same principle. The steam is conveyed through a pipe in a similar
manner, into the several vessels which contain the provisions to be
dressed, where it communicates to them its latent caloric, and returns
to the state of water. Count Rumford makes great use of this principle
in many of his fire-places: his grand maxim is to avoid all unnecessary
waste of caloric, for which purpose he confines the heat in such a
manner, that not a particle of it shall unnecessarily escape; and while
he economises the free caloric, he takes care also to turn the latent
heat to advantage. It is thus that he is enabled to produce a degree of
heat superior to that which is obtained in common fire-places, though he
employs less fuel.

EMILY.

When the advantages of such contrivances are so clear and plain,
I cannot understand why they are not universally used.

MRS. B.

A long time is always required before innovations, however useful, can
be reconciled with the prejudices of the vulgar.

EMILY.

What a pity it is that there should be a prejudice against new
inventions; how much more rapidly the world would improve, if such
useful discoveries were immediately and universally adopted!

MRS. B.

I believe, my dear, that there are as many novelties attempted to be
introduced, the adoption of which would be prejudicial to society, as
there are of those