d in the steam, of which the thermometer gives us no
account. This is latent heat.

Now, if you blow the steam into cold water instead of allowing
it to pass into the air, you will find that it heats the water
six times more than what is due to its indicated temperature. To
fix your ideas: suppose you take 100 lbs. of water at 60 deg., and
blow one pound of steam into it, making 101 lbs., its
temperature will now be about 72 deg., a rise of 12 deg. Return to
your 100 lbs. of water at 60 deg. and add one pound of water at 212
deg. the same temperature as the steam you added, and the temperature
will only be raised about 2 deg. The one pound of steam heats six
times more than the one pound of water, both being at the same
temperature. This is the quantity of latent heat, which means
simply hidden heat, in steam.

Proceeding further with the experiment, if, instead of allowing
the steam to blow into the water, you confine it until it gets
to some pressure, then blow it into the water, it takes the same
weight to raise the temperature to the same degree. This means
that the total heat remains practically the same, no matter at
what pressure.

This is James Watt's discovery, and it led him to the use of
high-pressure steam, used expansively.

Even coal may yet be superseded before it is exhausted, for as eminent
an authority as Professor Pritchett of the Massachusetts Institute of
Technology has said in a recent address:

Watt's invention and all it has led to is only a step on the way
to harnessing the forces of nature to the service of man. Do you
doubt that other inventions will work changes even more sweeping
than those which the steam engine has brought?

Consider a moment. The problem of which Watt solved a part is
not the problem of inventing a machine, but the problem of using
and storing the forces of nature which now go to waste. Now to
us who live on the earth there is only one source of power--the
sun. Darken the sun and every engine on the earth's surface
would soon stop, every wheel cease to turn, and all movement
cease. How prodigal this supply of power is we seldom stop to
consider. Deducting the atmospheric absorption, it is still true
that the sun delivers on each square yard of the earth's
surface, when he is shining, the equivalent of one horse-power
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