Caesar and Hannibal, through the
period of every event that history records, not merely our earth, but
the sun and the whole solar system with it, have been speeding their
way towards the star of which I speak on a journey of which we know
neither the beginning nor the end. We are at this moment thousands of
miles nearer to a Lyrae than we were a few minutes ago when I began
this discourse, and through every future moment, for untold thousands
of years to come, the earth and all there is on it will be nearer to a
Lyrae, or nearer to the place where that star now is, by hundreds of
miles for every minute of time come and gone. When shall we get there?
Probably in less than a million years, perhaps in half a million. We
cannot tell exactly, but get there we must if the laws of nature and
the laws of motion continue as they are. To attain to the stars was the
seemingly vain wish of an ancient philosopher, but the whole human race
is, in a certain sense, realizing this wish as rapidly as a speed of
ten miles a second can bring it about.

I have called attention to this motion because it may, in the not
distant future, afford the means of approximating to a solution of the
problem already mentioned--that of the extent of the universe.
Notwithstanding the success of astronomers during the present century
in measuring the parallax of a number of stars, the most recent
investigations show that there are very few, perhaps hardly more than a
score, of stars of which the parallax, and therefore the distance, has
been determined with any approach to certainty. Many parallaxes
determined about the middle of the nineteenth century have had to
disappear before the powerful tests applied by measures with the
heliometer; others have been greatly reduced and the distances of the
stars increased in proportion. So far as measurement goes, we can only
say of the distances of all the stars, except the few whose parallaxes
have been determined, that they are immeasurable. The radius of the
earth's orbit, a line more than ninety millions of miles in length, not
only vanishes from sight before we reach the distance of the great mass
of stars, but becomes such a mere point that when magnified by the
powerful instruments of modern times the most delicate appliances fail
to make it measurable. Here the solar motion comes to our help. This
motion, by which, as I have said, we are carried unceasingly through
space, is made evident by a motion of mo