endowed with exceptionally good vision can usually see
a few more. In an opera-glass the Pleiades becomes a beautiful
spectacle, though in a large telescope the stars appear too far apart
to make a really effective cluster. When Mr. Roberts took a photograph
of the Pleiades he placed a highly sensitive plate in his telescope,
and on that plate the Pleiades engraved their picture with their own
light. He left the plate exposed for hours, and on developing it not
only were the stars seen, but there were also patches of faint light
due to the presence of nebulae. It could not be said that the objects
on the plate were fallacious, for another photograph was taken, when
the same appearances were reproduced.

When we look at that pretty group of stars which has attracted
admiration during all time, we are to think that some of those stars
are merely the bright points in a vast nebula, invisible to our
unaided eyes or even to our mighty telescopes, though capable of
recording its trace on the photographic plate. Does not this give us a
greatly increased notion of the extent of the universe, when we
reflect that by photography we are enabled to see much which the
mightiest of telescopes had previously failed to disclose?

Of all the nebulae, numbering some thousands, there is but a single one
which can be seen without a telescope. It is in the constellation of
Andromeda, and on a clear dark night can just be seen with the unaided
eye as a faint stain of light on the sky. It has happened before now
that persons noticing this nebula for the first time have thought they
had discovered a comet. I would like you to try and find out this
object for yourselves.

If you look at it with an opera-glass it appears to be distinctly
elongated. You can see more of its structure when you view it in
larger instruments, but its nature was never made clear until some
beautiful photographs were taken by Mr. Roberts (Fig. 9).
Unfortunately, the nebula in Andromeda has not been placed in the best
position for its portrait from our point of view. It seems as if it
were a rather flat-shaped object, turned nearly edgewise towards us.
To look at the pattern on a plate, you would naturally hold the plate
so as to be able to look at it squarely. The pattern would not be seen
well if the plate were so tilted that its edge was turned towards you.
That seems to be nearly the way in which we are forced to view the
nebula in Andromeda. We can trace in the