tration: FIG. 22.--The Star-Cluster in the Centaur.]

Another of the most beautiful, on account of its regularity, is that of
the Centaur (Fig. 22).

These groups often assume the most extraordinary shapes in the
telescope, such as crowns, fishes, crabs, open mouths, birds with
outspread wings, etc.

We must also note the _gaseous nebulae_, universes in the making,
_e.g._, the famous Nebula in Orion, of which we obtained some notion a
while ago in connection with its sextuple star: and also that in
Andromeda (Fig. 23).

[Illustration: FIG. 23.--The Nebula in Andromeda.]

[Illustration: FIG. 24.--Nebula in the Greyhounds.]

Perhaps the most marvelous of all is that of the Greyhounds, which
evolves in gigantic spirals round a dazzling focus, and then loses
itself far off in the recesses of space. Fig. 24 gives a picture of it.

[Illustration: FIG. 25.--The Pleiades.]

Without going thus far, and penetrating into telescopic depths, my
readers can get some notion of these star-clusters with the help of a
small telescope or opera-glasses, or even with the unaided eye, by
looking at the beautiful group of the Pleiades, already familiar to us
on another page, and using it as a test of vision. The little map
subjoined (Fig. 25) will be an assistance in recognizing them, and in
estimating their magnitudes, which are in the following order:

Alcyone 3.0.
Electra 4.5.
Atlas 4.6.
Maia 5.0.
Merope 5.5.
Taygeta 5.8.
Pleione 6.3.
Celaeno 6.5.
Asterope 6.8.

Good eyes distinguish the first six, sharp sight detects the three
others.

In the times of the ancient Greeks, seven were accounted of equal
brilliancy, and the poets related that the seventh star had fled at the
time of the Trojan War. Ovid adds that she was mortified at not being
embraced by a god, as were her six sisters. It is probable that only the
best sight could then distinguish Pleione, as in our own day. The
angular distance from Atlas to Pleione is 5'.

The length of this republic, from Atlas and Pleione to Celaeno, is 4'/23"
of time, or 1 deg. 6' of arc; the breadth, from Merope to Asterope, is
36'.[8]

In the quadrilateral, the length from Alcyone to Electra is 36', and the
breadth from Merope to Maia 25'. To us it appears as though, if the Full
Moon were placed in front of this group of nine stars, she would cover
it entirel