Sidelights on Astronomy and Kindred Fields of Popular Science | Page 7

began by
trying to sound its depths; at one time he thought he had succeeded; but
before he died he saw that they were unfathomable with his most
powerful telescopes. Even today he would be a bold astronomer who
would profess to say with certainty whether the smallest stars we can
photograph are at the boundary of the system. Before we decide this
point we must have some idea of the form and distance of the cloudlike
masses of stars which form our great celestial girdle. A most curious

fact is that our solar system seems to be in the centre of this galactic
universe, because the Milky Way divides the heavens into two equal
parts, and seems equally broad at all points. Were we looking at such a
girdle as this from one side or the other, this appearance would not be
presented. But let us not be too bold. Perhaps we are the victims of
some fallacy, as Ptolemy was when he proved, by what looked like
sound reasoning, based on undeniable facts, that this earth of ours stood
at rest in the centre of the heavens!
A related problem, and one which may be of supreme importance to the
future of our race, is, What is the source of the heat radiated by the sun
and stars? We know that life on the earth is dependent on the heat
which the sun sends it. If we were deprived of this heat we should in a
few days be enveloped in a frost which would destroy nearly all
vegetation, and in a few months neither man nor animal would be alive,
unless crouching over fires soon to expire for want of fuel. We also
know that, at a time which is geologically recent, the whole of New
England was covered with a sheet of ice, hundreds or even thousands of
feet thick, above which no mountain but Washington raised its head. It
is quite possible that a small diminution in the supply of heat sent us by
the sun would gradually reproduce the great glacier, and once more
make the Eastern States like the pole. But the fact is that observations
of temperature in various countries for the last two or three hundred
years do not show any change in climate which can be attributed to a
variation in the amount of heat received from the sun.
The acceptance of this theory of the heat of those heavenly bodies
which shine by their own light--sun, stars, and nebulae--still leaves
open a problem that looks insoluble with our present knowledge. What
becomes of the great flood of heat and light which the sun and stars
radiate into empty space with a velocity of one hundred and eighty
thousand miles a second? Only a very small fraction of it can be
received by the planets or by other stars, because these are mere points
compared with their distance from us. Taking the teaching of our
science just as it stands, we should say that all this heat continues to
move on through infinite space forever. In a few thousand years it
reaches the probable confines of our great universe. But we know of no

reason why it should stop here. During the hundreds of millions of
years since all our stars began to shine, has the first ray of light and
heat kept on through space at the rate of one hundred and eighty
thousand miles a second, and will it continue to go on for ages to come?
If so, think of its distance now, and think of its still going on, to be
forever wasted! Rather say that the problem, What becomes of it? is as
yet unsolved.
Thus far I have described the greatest of problems; those which we may
suppose to concern the inhabitants of millions of worlds revolving
round the stars as much as they concern us. Let us now come down
from the starry heights to this little colony where we live, the solar
system. Here we have the great advantage of being better able to see
what is going on, owing to the comparative nearness of the planets.
When we learn that these bodies are like our earth in form, size, and
motions, the first question we ask is, Could we fly from planet to planet
and light on the surface of each, what sort of scenery would meet our
eyes? Mountain, forest, and field, a dreary waste, or a seething caldron
larger than our earth? If solid land there is, would we find on it the
homes of intelligent beings, the lairs of wild beasts, or no living thing
at all? Could we breathe the air, would we choke for breath or be
poisoned by the fumes of some noxious gas?
To most of