whole set of lines is unaltered
as a set, but everyone of them is shifted a tiny fraction up toward the
blue end of the spectrum, just a little displaced. Now if, instead of
advancing toward us, this same star had been rushing away from us at a
similar pace, all these lines would have been moved a tiny bit toward
the red or bass end of the spectrum. This is known to be certainly true,
so that by means of the spectroscope we can tell that some of these
great sun-stars are advancing toward us and some receding from us,
according to whether the multitudes of little lines in the spectrum are
shifted slightly to the blue or the red end.

You remember that it has been surmised that the pace the sun moves with
his system is about twelve miles a second. This seems fast enough to us,
who think that one mile a minute is good time for an express train, but
it is slow compared with the pace of many of the stars. As I have said,
some are travelling at a rate of between two hundred and three hundred
miles a second; and it is due to the spectroscope that we know not only
whether a star is advancing toward us or receding from us, but also
whether the pace is great or not; it even tells us what the pace is, up
to about half a mile a second, which is very marvellous. It is a curious
fact that many of the small stars show greater movement than the large
ones, which mayor may not mean that they are nearer to us.

It may be taken as established that there is no such thing as absolute
rest in the universe: everything, stars and nebulae alike, are moving
somewhere; in an infinite variety of directions, with an infinite
variety of speed they hasten this way and that. It would be impossible
for any to remain still, for even supposing it had been so 'in the
beginning,' the vast forces at work in the universe would not let it
remain so. Out of space would come the persistent call of gravitation:
atoms would cry silently to atoms. There could be no perfect equality
of pull on all sides; from one side or another the pull would be the
stronger. Slowly the inert mass would obey and begin falling toward it;
it might be an inch at a time, but with rapid increase, until at last it
also was hastening some whither in this universe which appears to us to
be infinite.

It must be remembered that these stars, even when moving at an enormous
pace, do not change their places in the sky when regarded by ordinary
observers. It would take thousands of years fo