sense they are justly called little, for each of them occupies but
a very small spot in the sky as compared with that which would be
filled by an ordinary cloud in our air. The nebulae are, however,
objects of the most stupendous proportions. Were our earth and
thousands of millions of bodies quite as big all put together, they
would not be nearly so great as one of these nebulae. Astronomers
reckon up the various nebulae by thousands, but I must add that most of
them are apparently faint and uninteresting. A nebula is sometimes
liable to be mistaken for a comet. The comet is, as I have already
explained, at once distinguished by the fact that it is moving and
changing its appearance from hour to hour, while scores of years
elapse without changes in the aspect or position of a nebula. The most
powerful telescopes are employed in observing these faint objects. I
take this opportunity of showing a picture of an instrument suitable
for such observations. It is the great reflector of the Paris
Observatory (Fig. 5).

[Illustration: FIG. 5. A GREAT REFLECTING TELESCOPE.]

[Illustration: FIG. 6. THE RING NEBULA IN LYRA, UNDER DIFFERENT
TELESCOPIC POWERS.]

There are such multitudes of nebulae that I can only show a few of the
more remarkable kinds. In Fig. 6 will be seen pictures of a curious
object in the constellation of Lyra seen under different telescopic
powers. This is a gigantic ring of luminous gas. To judge of the size
of this ring let us suppose that a railway were laid across it, and
the train you entered at one side was not to stop until it reached the
other side, how long do you think this journey would require? I
recollect some time ago a picture in _Punch_ which showed a train
about to start from London to Brighton, and the guard walking up and
down announcing to the passengers the alarming fact that "this train
stops nowhere." An old gentleman was seen vainly gesticulating out of
the window and imploring to be let out ere the frightful journey was
commenced. In the nebular railway the passengers would almost require
such a warning.

Let the train start at a speed of a mile a minute, you would think,
surely, that it must soon cross the ring. But the minutes pass, an
hour has elapsed; so the distance must be sixty miles at all events.
The hours creep on into days, the days advance into years, and still
the train goes on. The years would lengthen out into centuries, and
even when the train had been rushing on