ustains cosmic bodies in their relative positions. The
primitive notion of a material frame and the confining dome of the
ancients were abandoned. We know now that a framework of the most
massive steel would be too frail to hold together even the moon and the
earth. It would be rent by the strain. The action of gravitation is the
all-sustaining power. Once introduce that idea, and the great ocean of
ether might stretch illimitably on every side, and the vastest bodies
might be scattered over it and traverse it in stupendous paths. Thus it
came about that, as the little optic tube of Galilei slowly developed
into the giant telescope of Herschel, and then into the powerful
refracting telescopes of the United States of our time; as the new
science of photography provided observers with a new eye--a sensitive
plate that will register messages, which the human eye cannot detect,
from far-off regions; and as a new instrument, the spectroscope, endowed
astronomers with a power of perceiving fresh aspects of the inhabitants
of space, the horizon rolled backward, and the mind contemplated a
universe 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 t