ig
three tons of coal and set that to do his work and then die, because
his work will be better done, and without any cost for the
maintenance of the doer.

Come down below the color vibrations, and we shall find that those
which are too infrequent to be visible, manifest as heat. Naturally
there will be as many different kinds of heat as tints of color,
because there is as great a range of numbers of vibration. It is
our privilege to sift them apart and sort them over, and find what
kinds are best adapted to our various uses.

Take an electric lamp, giving a strong beam of light and heat, and
with a plano-convex lens gather it into a single beam and direct
it upon a thermometer, twenty feet away, that is made of glass
and filled with air. The [Page 32] expansion or contraction of this
air will indicate the varying amounts of heat. Watch your
air-thermometer, on which the beam of heat is pouring, for the
result. There is none. And yet there is a strong current of heat
there. Put another kind of test of heat beyond it and it appears;
coat the air-thermometer with a bit of black cloth, and that will
absorb heat and reveal it. But why not at first? Because the glass
lens stops all the heat that can affect glass. The twenty feet of
air absorbs all the heat that affects air, and no kind of heat is
left to affect an instrument made of glass and air; but there are
kinds of heat enough to affect instruments made of other things.

A very strong current of heat may be sent right through the heart
of a block of ice without melting the ice at all or cooling off
the heat in the least. It is done in this way: Send the beam of
heat through water in a glass trough, and this absorbs all the heat
that can affect water or ice, getting itself hot, and leaving all
other kinds of heat to go through the ice beyond; and appropriate
tests show that as much heat comes out on the other side as goes
in on this side, and it does not melt the ice at all. Gunpowder
may be exploded by heat sent through ice. Dr. Kane, years ago,
made this experiment. He was coming down from the north, and fell
in with some Esquimaux, whom he was anxious to conciliate. He said
to the old wizard of the tribe, "I am a wizard; I can bring the
sun down out of the heavens with a piece of ice." That was a good,
deal to say in a country where there was so little sun. "So," he
writes, "I took my hatchet, chipped a small piece of ice into the
form of a double-convex lens, [