o antipodal
regions of the heavens.

Another unity marked with yet more precision is seen in the chemical
elements of which stars are composed. We know that the sun is composed
of the same elements which we find on the earth and into which we
resolve compounds in our laboratories. These same elements are found in
the most distant stars. It is true that some of these bodies seem to
contain elements which we do not find on earth. But as these unknown
elements are scattered from one extreme of the universe to the other,
they only serve still further to enforce the unity which runs through
the whole. The nebulae are composed, in part at least, of forms of
matter dissimilar to any with which we are acquainted. But, different
though they may be, they are alike in their general character
throughout the whole field we are considering. Even in such a feature
as the proper motions of the stars, the same unity is seen. The reader
doubtless knows that each of these objects is flying through space on
its own course with a speed comparable with that of the earth around
the sun. These speeds range from the smallest limit up to more than one
hundred miles a second. Such diversity might seem to detract from the
unity of the whole; but when we seek to learn something definite by
taking their average, we find this average to be, so far as can yet be
determined, much the same in opposite regions of the universe. Quite
recently it has become probable that a certain class of very bright
stars known as Orion stars--because there are many of them in the most
brilliant of our constellations--which are scattered along the whole
course of the Milky Way, have one and all, in the general average,
slower motions than other stars. Here again we have a definable
characteristic extending through the universe. In drawing attention to
these points of similarity throughout the whole universe, it must not
be supposed that we base our conclusions directly upon them. The point
they bring out is that the universe is in the nature of an organized
system; and it is upon the fact of its being such a system that we are
able, by other facts, to reach conclusions as to its structure, extent,
and other characteristics.

One of the great problems connected with the universe is that of its
possible extent. How far away are the stars? One of the unities which
we have described leads at once to the conclusion that the stars must
be at very different distances from us;