is lowered, but not to the freezing
point. The diminution of heat, as you know, produces a contraction in
the bulk of fluids, as well as of solids. This effect, however, does not
take place in water below the temperature of 40 degrees, which is 8
degrees above the freezing point. At that temperature, therefore, the
internal motion, occasioned by the increased specific gravity of the
condensed particles, ceases; for when the water at the surface no longer
condenses, it will no longer descend, and leave a fresh surface exposed
to the atmosphere: this surface alone, therefore, will be further
exposed to its severity, and will soon be brought down to the freezing
point, when it becomes ice, which being a bad conductor of heat,
preserves the water beneath a long time from being affected by the
external cold.

CAROLINE.

And the sea does not freeze, I suppose, because its depth is so great,
that a frost never lasts long enough to bring down the temperature of
such a great body of water to 40 degrees?

MRS. B.

That is one reason why the sea, as a large mass of water, does not
freeze. But, independently of this, salt water does not freeze till it
is cooled much below 32 degrees, and with respect to the law of
condensation, salt water is an exception, as it condenses even many
degrees below the freezing point. When the caloric of fresh water,
therefore, is imprisoned by the ice on its surface, the ocean still
continues throwing off heat into the atmosphere, which is a most signal
dispensation of Providence to moderate the intensity of the cold in
winter.

CAROLINE.

This theory of the non-conducting power of liquids, does not, I suppose,
hold good with respect to air, otherwise the atmosphere would not be
heated by the rays of the sun passing through it?

MRS. B.

Nor is it heated in that way. The pure atmosphere is a perfectly
transparent medium, which neither radiates, absorbs, nor conducts
caloric, but transmits the rays of the sun to us without in any way
diminishing their intensity. The air is therefore not more heated, by
the sun's rays passing through it, than diamond, glass, water, or any
other transparent medium.

CAROLINE.

That is very extraordinary! Are glass windows not heated then by the sun
shining on them?

MRS. B.

No; not if the glass be perfectly transparent. A most convincing proof
that glass transmits the rays of the sun without being heated by them is
afforded by the burning lens, which