ignition of all the coal in every coal-pit in the globe has been
dispersed and totally lost to the sun.

But we have still one further conception to introduce before we shall
have fully grasped the significance of the sun's extravagance in the
matter of heat. As the sun shines to-day on this earth, so it shone
yesterday, so it shone a hundred years ago, a thousand years ago; so
it shone in the earliest dawn of history; so it shone during those
still remoter periods when great animals flourished which have now
vanished forever; so it shone during that remarkable period in earth's
history when the great coal forests flourished; so it shone in those
remote ages many millions of years ago when life began to dawn on an
earth which was still young. There is every reason to believe that
throughout these illimitable periods which the imagination strives in
vain to realize, the sun has dispensed its radiant treasures of light
and warmth with just the same prodigality as that which now
characterizes it.

We all know the consequences of wanton extravagance. We know it spells
bankruptcy and ruin. The expenditure of heat by the sun is the most
magnificent extravagance of which human knowledge gives us any
conception. How have the consequences of such awful prodigality been
hitherto averted? How is it that the sun is still able to draw on its
heat reserves from second to second, from century to century, from eon
to eon, ever squandering two thousand million times as much heat as
that which genially warms our temperate regions, as that which draws
forth the exuberant vegetation of the tropics, or which rages in the
Desert of Sahara? This is indeed a great problem.

It was Helmholtz who discovered that the continual maintenance of the
sun's temperature is due to the fact that the sun is neither solid nor
liquid, but is to a great extent gaseous. His theory of the subject
has gained universal acceptance. Those who have taken the trouble to
become acquainted with it are compelled to admit that the doctrine set
forth by this great philosopher embodies a profound truth.

[Illustration: A TYPICAL SUN-SPOT.

By permission of Longmans, Green & Co., from "Old and New Astronomy,"
by Richard A. Proctor.]

Even the great sun cannot escape the application of a certain law
which affects every terrestrial object, and whose province is wide as
the universe itself. Nature has not one law for the rich and another
for the poor. The sun is sheddi