The steps to a
conclusion on the subject are briefly these: First, we have a
general conclusion, the basis of which I have already set forth,
that, to use a loose expression, there are likenesses throughout
the whole diameter of the universe. There is, therefore, no reason
to suppose that the region in which our system is situated differs
in any essential degree from any other region near the central
portion. Again, spectroscopic examinations seem to show that all
the stars are in motion, and that we cannot say that those in one
part of the universe move more rapidly than those in another. This
result is of the greatest value for our purpose, because, when we
consider only the apparent motions, as ordinarily observed, these
are necessarily dependent upon the distance of the star. We
cannot, therefore, infer the actual speed of a star from ordinary
observations until we know its distance. But the results of
spectroscopic measurements of radial velocity are independent of
the distance of the star.
But let us not claim too much. We cannot yet say with certainty
that the stars which form the agglomerations of the Milky Way
have, beyond doubt, the same average motion as the stars in other
regions of the universe.
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