invisible.

EMILY.

Do you think it possible that heat may be merely a modification of
light?

MRS. B.

That is a supposition which, in the present state of natural philosophy,
can neither be positively affirmed nor denied. Let us, therefore,
instead of discussing theoretical points, be contented with examining
what is known respecting the chemical effects of light.

Light is capable of entering into a kind of transitory union with
certain substances, and this is what has been called phosphorescence.
Bodies that are possessed of this property, after being exposed to the
sun's rays, appear luminous in the dark. The shells of fish, the bones
of land animals, marble, limestone, and a variety of combinations of
earths, are more or less powerfully phosphorescent.

CAROLINE.

I remember being much surprised last summer with the phosphorescent
appearance of some pieces of rotten wood, which had just been dug out of
the ground; they shone so bright that I at first supposed them to be
glow-worms.

EMILY.

And is not the light of a glow-worm of a phosphorescent nature?

MRS. B.

It is a very remarkable instance of phosphorescence in living animals;
this property, however, is not exclusively possessed by the glow-worm.
The insect called the lanthorn-fly, which is peculiar to warm climates,
emits light as it flies, producing in the dark a remarkably sparkling
appearance. But it is more common to see animal matter in a dead state
possessed of a phosphorescent quality; sea fish is often eminently so.

EMILY.

I have heard that the sea has sometimes had the appearance of being
illuminated, and that the light is supposed to proceed from the spawn of
fishes floating on its surface.

MRS. B.

This light is probably owing to that or some other animal matter. Sea
water has been observed to become luminous from the substance of a fresh
herring having been immersed in it; and certain insects, of the Medusa
kind, are known to produce similar effects.

But the strongest phosphorescence is produced by chemical compositions
prepared for the purpose, the most common of which consists of oyster
shells and sulphur, and is known by the name of Canton's Phosphorus.

EMILY.

I am rather surprised, Mrs. B., that you should have said so much of the
light emitted by phosphorescent bodies without taking any notice of that
which is produced by burning bodies.

MRS. B.

The light emitted by the latter is so intimately connected