e position shown on p. 413. In the year 1885 a new
star of the seventh magnitude suddenly appeared close to the brightest
part of the nebula, and declined again to invisibility after the lapse
of a few months.

The nebula in Lyra is the most conspicuous ring nebula in the heavens,
but it is not to be supposed that it is the only member of this class.
Altogether, there are about a dozen of these objects. It seems difficult
to form any adequate conception of the nature of such a body. It is,
however, impossible to view the annular nebulae without being, at all
events, reminded of those elegant objects known as vortex rings. Who has
not noticed a graceful ring of steam which occasionally escapes from the
funnel of a locomotive, and ascends high into the air, only dissolving
some time after the steam not so specialised has disappeared? Such
vortex rings can be produced artificially by a cubical box, one open
side of which is covered with canvas, while on the opposite side of the
box is a circular hole. A tap on the canvas will cause a vortex ring to
start from the hole; and if the box be filled with smoke, this ring will
be visible for many feet of its path. It would certainly be far too much
to assert that the annular nebulae have any real analogy to vortex rings;
but there is, at all events, no other object known to us with which they
can be compared.

The heavens contain a number of minute but brilliant objects known as
the planetary nebulae. They can only be described as globes of glowing
bluish-coloured gas, often small enough to be mistaken for a star when
viewed through a telescope. One of the most remarkable of these objects
lies in the constellation Draco, and can be found half-way between the
Pole Star and the star g Draconis. Some of the more recently
discovered planetary nebulae are extremely small, and they have indeed
only been distinguished from small stars by the spectroscope. It is also
to be noticed that such objects are a little out of the stellar focus in
the refracting telescope in consequence of their blue colour. This
remark does not apply to a reflecting telescope, as this instrument
conducts all the rays to a common focus.

There are many other forms of nebulae: there are long nebulous rays;
there are the wondrous spirals which have been disclosed in Lord Rosse's
great reflector; there are the double nebulae. But all these various
objects we must merely dismiss with this passing reference. There i