un as we know it. What then keeps it shining?
It is still contracting, but slowly, so slowly that it is quite
imperceptible to our finest instruments. It has been calculated that if
it contracts two hundred and fifty feet in diameter in a year, the
energy thus gained and turned into heat is quite sufficient to account
for its whole yearly output. This is indeed marvellous. In comparison
with the sun's size two hundred and fifty feet is nothing. It would take
nine thousand years at this rate before any diminution could be noticed
by our finest instruments! Here is a source of heat which can continue
for countless ages without exhaustion. Thus to all intents and purposes
we may say the sun's shining is inexhaustible. Yet we must follow out
the train of reasoning, and see what will happen in the end, in eras and
eras of time, if nothing intervenes. Well, some gaseous bodies are far
finer and more tenuous than others, and when a gaseous body contracts it
is all the time getting denser; as it grows denser and denser it at last
becomes liquid, and then solid, and then it ceases to contract, as of
course the particles of a solid body cannot fall freely toward the
centre, as those of a gaseous body can. Our earth has long ago reached
this stage. When solid the action ceases, and the heat is no more kept
up by this source of energy, therefore the body begins to cool--surface
first, and lastly the interior; it cools more quickly the smaller it is.
Our moon has parted with all her heat long ago, while the earth still
retains some internally. In the sun, therefore, we have an object-lesson
of the stages through which all the planets must have passed. They have
all once been glowing hot, and some may be still hot even on the
surface, as we have seen there is reason to believe is the case with
Jupiter.

By this marvellous arrangement for the continued heat of the sun we can
see that the warmth of our planets is assured for untold ages. There is
no need to fear that the sun will wear out by burning. His brightness
will continue for ages beyond the thoughts of man.

Besides this, a few other things have been discovered about him. He is,
of course, exceptionally difficult to observe; for though he is so
large, which should make it easy, he is so brilliant that anyone
regarding him through a telescope without the precaution of prepared
glasses to keep off a great part of the light would be blinded at once.
One most remarkable fact about