the Constellation of the Serpent, which shone for a year; of 1866, of
second magnitude, in the Northern Crown, which appeared for a few weeks
only; of 1876, in the Swan; of 1885, in the Nebula of Andromeda; of
1891, in the Charioteer; and quite recently, of 1901, in Perseus.

These temporary stars, which appear spontaneously to the observers on
the Earth, and quickly vanish again, are doubtless due to collisions,
conflagrations, or celestial cataclysms. But we only see them long after
the epoch at which the phenomena occurred, years upon years, and
centuries ago. For instance, the conflagration photographed by the
author in 1901, in Perseus, must have occurred in the time of Queen
Elizabeth. It has taken all this time for the rays of light to reach us.

* * * * *

The Heavens are full of surprises, on which we can bestow but a fleeting
glance within these limits. They present a field of infinite variety.

Who has not noticed the Milky Way, the pale belt that traverses the
entire firmament and is so luminous on clear evenings in the
Constellations of the Swan and the Lyre? It is indeed a swarm of stars.
Each is individually too small to excite our retina, but as a whole,
curiously enough, they are perfectly visible. With opera-glasses we
divine the starry constitution: a small telescope shows us marvels.
Eighteen millions of stars were counted there with the gauges of William
Herschel.

Now this Milky Way is a symbol, not of the Universe, but of the
Universes that succeed each other through the vast spaces to Infinity.

Our Sun is a star of the Milky Way. It surrounds us like a great circle,
and if the Earth were transparent, we should see it pass beneath our
feet as well as over our heads. It consists of a very considerable mass
of star-clusters, varying greatly in extent and number, some projected
in front of others, while the whole forms an agglomeration.

[Illustration: FIG. 21.--The Star-Cluster in Hercules.]

Among this mass of star-groups, several thousands of which are already
known to us, we will select one of the most curious, the Cluster in
Hercules, which can be distinguished with the unaided eye, between the
stars [eta] and [zeta] of that constellation. Many photographs of it
have been taken in the author's observatory at Juvisy, showing some
thousands of stars; and one of these is reproduced in the accompanying
figure (Fig. 21). Is it not a veritable universe?

[Illus