of
the nail I squeeze out some of the heat. That was the old theory. One
single experiment knocked it on the head. It was certain, that in water
there is a great deal more entrapped heat--"latent heat" it was
called--than there is in ice. If you take two pieces of ice and rub them
together, you will find the ice melts--the solid ice changes (that is to
say) into liquid water. Where did the heat come from to melt the ice?
You could not get the heat _from_ the ice, because it was not there,
there being admittedly more latent heat in the water than in the ice.
The explanation is certain--the heat was the result of the friction. And
now let me go to my hammer and nail. I wish to see whether I can make
this nail hot by hammering. It is quite cold at the present time. I hope
to make the nail hot enough by hammering it to fire that piece of
phosphorus (Fig. 24). One or two sharp blows with the hammer suffice,
and as you see the thing is done--_I_ have fired the phosphorus. But
follow the precise details of the experiment. It was _I_ who gave motion
to the hammer. _I_ brought that hammer on to that nail. Where did the
motion go to that I gave the hammer? It went into the nail, and it is
that very motion that made the nail hot, and it was that heat which
lighted the phosphorus. It was _I_ who fired the phosphorus: do not be
mistaken, _I_ fired the phosphorus. It was my arm that gave motion to
the hammer. It was my force that was communicated to the hammer. It was
_I_ who made the hammer give the motion to the nail. It was _I_ myself
that fired the phosphorus.

[Illustration: Fig. 24.]

I want you then to realize this great fact, that when I hold the steel
and strike it with the flint, and get sparks, I first of all knock off a
minute fragment of iron by the blow that I impart to it, whilst the
force I use in striking the blow actually renders the little piece of
detached iron red-hot. What a wonderful thought this is! Look at the
sun, the great centre of heat! It looks as if it were a blazing ball of
fire in the heavens. Where does the heat of the sun come from? It seems
bold to suggest that the heat is produced by the impact of meteorites on
the sun. Just as I, for instance, take a hammer and heat the nail by the
dash of the hammer on it, so the dash of these meteorites on the sun are
supposed to produce the heat so essential to our life and comfort.

[Illustration: Fig. 25.]

[Illustration: Fig. 26.]

[Illustrati