at the expiration of four hours, it
regains its former brilliancy, which it sustains for two days and
thirteen hours, when it again goes through the same cycle of changes in
a precisely similar manner to what has been described. Astrologers have
ascribed many evil influences to the demon star, which adorned the head
of Medusa; nor did it escape the observation of ancient astronomers that
this malevolent orb is--as a modern writer amusingly remarks--slowly
winking at us from out the depths of space.

Variable stars are found in greater numbers in some parts of the heavens
than in others. Those of a white colour, and with shorter and more
regular periods, are most numerous in the region of the Milky Way; those
that are small, with long periods and of a reddish hue, are more widely
removed from that zone. Stars of this class are all very remote, and no
attempt has as yet been made to ascertain the parallax of Algol.

Several theories have been suggested in order to account for the
periodical brilliancy of those stars. It has been suggested that the
stars have opaque non-luminous patches on their surfaces, and that
during axial rotation their light ebbs and flows according as the dark
or bright portions are turned towards us. This theory is highly
improbable. Another and more plausible reason, especially with regard to
short period variables, is, that around those stars there revolve opaque
bodies or satellites which at times intercept a portion of their light
by producing a partial eclipse of their discs, similar to that caused by
the dark body of the Moon when passing between the Sun and the Earth.

It is now known that in the case of variables of the Algol type, the
periodical fluctuations of their light arises from this cause, and that
round Algol there is a dark world or satellite travelling, which
completes a revolution of its orbit in about sixty-nine hours, and that,
during each circuit, it intercepts one half of the light of its primary
by partially eclipsing the orb, and thereby creating a diminution in its
apparent magnitude which becomes perceptible at recurring intervals.

STAR GROUPS.--These are plentifully scattered over the heavens and, by
their conspicuous brilliancy, add to the grandeur and magnificence of
the midnight sky. The Hyades in Taurus, of which Aldebaran is the chief,
forming the eye of the Bull, attract attention.

The stars in Coma Bernices form a rich group; the sickle in Leo, the
seven s