The Story of Evolution | Page 7

of colossal extent and power.

Let us try to conceive this universe before we study its evolution. I do
not adopt any of the numerous devices that have been invented for the
purpose of impressing on the imagination the large figures we must use.
One may doubt if any of them are effective, and they are at least
familiar. Our solar system--the family of sun and planets which had
been sheltered under a mighty dome resting on the hill-tops--has turned
out to occupy a span of space some 16,000,000,000 miles in diameter.
That is a very small area in the new universe. Draw a circle, 100 billion
miles in diameter, round the sun, and you will find that it contains only
three stars besides the sun. In other words, a sphere of space measuring
300 billion miles in circumference--we will not venture upon the
number of cubic miles--contains only four stars (the sun, alpha
Centauri, 21,185 Lalande, and 61 Cygni). However, this part of space
seems to be below the average in point of population, and we must
adopt a different way of estimating the magnitude of the universe from
the number of its stellar citizens.
Beyond the vast sphere of comparatively empty space immediately
surrounding our sun lies the stellar universe into which our great
telescopes are steadily penetrating. Recent astronomers give various
calculations, ranging from 200,000,000 to 2,000,000,000, of the
number of stars that have yet come within our faintest knowledge. Let
us accept the modest provisional estimate of 500,000,000. Now, if we
had reason to think that these stars were of much the same size and
brilliance as our sun, we should be able roughly to calculate their
distance from their faintness. We cannot do this, as they differ
considerably in size and intrinsic brilliance. Sirius is more than twice
the size of our sun and gives out twenty times as much light. Canopus
emits 20,000 times as much light as the sun, but we cannot say, in this
case, how much larger it is than the sun. Arcturus, however, belongs to
the same class of stars as our sun, and astronomers conclude that it
must be thousands of times larger than the sun. A few stars are known
to be smaller than the sun. Some are, intrinsically, far more brilliant;
some far less brilliant.
Another method has been adopted, though this also must be regarded
with great reserve. The distance of the nearer stars can be positively
measured, and this has been done in a large number of cases. The
proportion of such cases to the whole is still very small, but, as far as

the results go, we find that stars of the first magnitude are, on the
average, nearly 200 billion miles away; stars of the second magnitude
nearly 300 billion; and stars of the third magnitude 450 billion. If this
fifty per cent increase of distance for each lower magnitude of stars
were certain and constant, the stars of the eighth magnitude would be
3000 billion miles away, and stars of the sixteenth magnitude would be
100,000 billion miles away; and there are still two fainter classes of
stars which are registered on long-exposure photographs. The mere
vastness of these figures is immaterial to the astronomer, but he warns
us that the method is uncertain. We may be content to conclude that the
starry universe over which our great telescopes keep watch stretches for
thousands, and probably tens of thousands, of billions of miles. There
are myriads of stars so remote that, though each is a vast incandescent
globe at a temperature of many thousand degrees, and though their light
is concentrated on the mirrors or in the lenses of our largest telescopes
and directed upon the photographic plate at the rate of more than 800
billion waves a second, they take several hours to register the faintest
point of light on the plate.
When we reflect that the universe has grown with the growth of our
telescopes and the application of photography we wonder whether we
may as yet see only a fraction of the real universe, as small in
comparison with the whole as the Babylonian system was in
comparison with ours. We must be content to wonder. Some affirm that
the universe is infinite; others that it is limited. We have no firm ground
in science for either assertion. Those who claim that the system is
limited point out that, as the stars decrease in brightness, they increase
so enormously in number that the greater faintness is more than
compensated, and therefore, if there were an infinite series of
magnitudes, the midnight sky would be a blaze of light. But this
theoretical reasoning does not allow for dense regions of space that
may obstruct the light, or vast regions of vacancy between