aphed are
visible to the eye, even with the most powerful telescope.

This demonstration of what the reflecting telescope can do may be
regarded as one of the most important discoveries of our time as to the
capabilities of astronomical instruments. It has long been known that
the image formed in the focus of the best refracting telescope is
affected by an imperfection arising from the different action of the
glasses on rays of light of different colors. Hence, the image of a
star can never be seen or photographed with such an instrument, as an
actual point, but only as a small, diffused mass. This difficulty is
avoided in the reflecting telescope; but a new difficulty is found in
the bending of the mirror under the influence of its own weight.
Devices for overcoming this had been so far from successful that, when
Mr. Crossley presented his instrument to the Lick Observatory, it was
feared that little of importance could be done with it. But as often
happens in human affairs outside the field of astronomy, when ingenious
and able men devote their attention to the careful study of a problem,
it was found that new results could be reached. Thus it was that,
before a great while, what was supposed to be an inferior instrument
proved not only to have qualities not before suspected, but to be the
means of making an important addition to the methods of astronomical
investigation.

In order that our knowledge of the position of a star may be complete,
we must know its distance. This can be measured only through the star's
parallax--that is to say, the slight change in its direction produced
by the swing of our earth around its orbit. But so vast is the distance
in question that this change is immeasurably small, except for,
perhaps, a few hundred stars, and even for these few its measurement
almost baffles the skill of the most expert astronomer. Progress in
this direction is therefore very slow, and there are probably not yet a
hundred stars of which the parallax has been ascertained with any
approach to certainty. Dr. Chase is now completing an important work of
this kind at the Yale Observatory.

To the most refined telescopic observations, as well as to the naked
eye, the stars seem all alike, except that they differ greatly in
brightness, and somewhat in color. But when their light is analyzed by
the spectroscope, it is found that scarcely any two are exactly alike.
An important part of the work of the astro-physical o