deed, so slowly that during the century they have been
under observation only the very faintest sign of movement has been
detected; and in other systems, which we are bound to suppose double,
the stars are so slow in their movements that no progress seems to have
been made at all.

The star we know as the nearest to us in the heavens, Alpha Centauri, is
composed of two very bright partners, which take about eighty-seven
years to traverse their orbit. They sometimes come as near to each other
as Saturn is to the sun. In the case of Sirius astronomers found out
that he had a companion by reason of his irregularities of movement
before they discovered that companion, which is apparently a very small
star, only to be discerned with good telescopes. But here, again, it
would be unwise to judge only by what we see. Though the star appears
small, we know by the influence it exercises on Sirius that it is very
nearly the same size as he is. Thus we judge that it is poor in
light-giving property; in fact, its shining power is much less than that
of its companion, though its size is so nearly equal. This is not
wonderful, for Sirius's marvellous light-giving power is one of the
wonders of the universe; he shines as brilliantly as twenty-nine or
thirty of our suns!

In some cases the dark body which we cannot see may even be larger than
the shining one, through which alone we can know anything of it. Here we
have a new idea, a hint that in some of these systems there may be a
mighty earth with a smaller sun going round it, as men imagined our sun
went around the earth before the real truth was found out.

So we see that, when we speak of the stars as suns comparable with our
sun, we cannot think of them all as being exactly on the same model.
There are endless varieties in the systems; there are solitary suns like
ours which may have a number of small planets going round them, as in
the solar system; but there are also double suns going round each other,
suns with mighty dark bodies revolving round them which may be planets,
and huge dark bodies with small suns too. Every increase of knowledge
opens up new wonders, and the world in which we live is but one kind of
world amid an infinite number.

In this chapter we have learnt an altogether new fact--the fact that the
hosts of heaven comprise not only those shining stars we are accustomed
to see, but also dark bodies equally massive, and probably equally
numerous, which we cann