ygni moves
at present in a path very nearly straight, and with a velocity very
nearly uniform.

As the distance of 61 Cygni from the sun is forty billions of miles, and
its velocity is thirty miles a second, it is easy to find how long the
star would take to accomplish a journey equal to its distance from the
sun. The time required will be about 40,000 years. In the last 400,000
years 61 Cygni will have moved over a distance ten times as great as
its present distance from the sun, whatever be the direction of motion.
This star must therefore have been about ten times as far from the earth
400,000 years ago as it is at present. Though this epoch is incredibly
more remote than any historical record, it is perhaps not incomparable
with the duration of the human race; while compared with the vast lapse
of geological time, such periods seem trivial and insignificant.
Geologists have long ago repudiated mere thousands of years; they now
claim millions, and many millions of years, for the performance of
geological phenomena. If the earth has existed for the millions of years
which geologists assert, it becomes reasonable for astronomers to
speculate on the phenomena which have transpired in the heavens in the
lapse of similar ages. By the aid of our knowledge of star distances,
combined with an assumed velocity of thirty miles per second, we can
make the attempt to peer back into the remote past, and show how great
are the changes which our universe seems to have undergone.

In a million years 61 Cygni will apparently have moved through a
distance which is twenty-five times as great as its present distance
from the sun. Whatever be the direction in which 61 Cygni is
moving--whether it be towards the earth or from the earth, to the right
or to the left, it must have been about twenty-five times as far off a
million years ago as it is at present; but even at its present distance
61 Cygni is a small star; were it ten times as far it could only be seen
with a good telescope; were it twenty-five times as far it would barely
be a visible point in our greatest telescopes.

The conclusions arrived at with regard to 61 Cygni may be applied with
varying degrees of emphasis to other stars. We are thus led to the
conclusion that many of the stars with which the heavens are strewn are
apparently in slow motion. But this motion though apparently slow may
really be very rapid. When standing on the sea-shore, and looking at a
steamer on th