a telescope, and was known to the ancients; it is
believed to have been mentioned in a book of the tenth century!

If you take an imaginary line down from the two left-hand stars of
Cassiopeia, and follow it carefully, you will come before long to a
rather faint star, and close to it is the nebula.

When you catch sight of it you will, perhaps, at first be disappointed,
for all you will see is a soft blur of white, as if someone had laid a
dab of luminous paint on the sky with a finger; but as you gaze at it
night after night and realize its unchangeableness, realize also that it
is a mass of glowing gas, an island in space, infinitely distant,
unsupported and inexplicable, something of the wonder of it will creep
over you.

[Illustration: _Dr. Max Wolf._

THE GREAT NEBULA IN ANDROMEDA.]

Thousands of telescopic nebulae are now known, and have been examined,
and they are of all shapes. Roughly, they have been divided up into
several classes--those that seem to us to be round and those that are
long ovals, like this one in Andromeda; but these may, of course, be
only round ones seen edgewise by us; others are very irregular, and
spread over an enormous part of the sky. The most remarkable of these is
that in Orion, and if you look very hard at the middle star in the
sword-hilt of Orion, you may be able to make out a faint mistiness.
This, when seen through a telescope, becomes a wonderful and
far-spreading nebula, with brighter and darker parts like gulfs in
it, and dark channels. It has been sometimes called the Fish-mouth
Nebula, from a fanciful idea as to its shape. Indeed, so extraordinarily
varied are these curious structures, that they have been compared with
numbers of different objects. We have some like brushes, others
resembling fans, rings, spindles, keyholes; others like animals--a fish,
a crab, an owl, and so on; but these suggestions are imaginative, and
have nothing to do with the real problem. In _The System of the Stars_
Miss Clerke says: 'In regarding these singular structures we seem to see
surges and spray-flakes of a nebulous ocean, bewitched into sudden
immobility; or a rack of tempest-driven clouds hanging in the sky,
momentarily awaiting the transforming violence of a fresh onset.
Sometimes continents of pale light are separated by narrow straits of
comparative darkness; elsewhere obscure spaces are hemmed in by luminous
inlets and channels.'

One curious point about the Orion Nebula is tha