a half days. Dr. A. W. Roberts finds
that the bodies are revolving around each other in actual contact.

_Temporary stars_ are stars which have suddenly blazed out in regions of
the sky where no star was previously seen, and have faded away more or
less gradually.

It was the appearance of such a star, in the year 134 B.C., which
prompted Hipparchus to make his celebrated catalogue, with the object of
leaving a record by which future observers could note celestial changes.
In 1572 another star of this kind flashed out in the constellation of
Cassiopeia (see Plate XIX., p. 292), and was detected by Tycho Brahe. It
became as bright as the planet Venus, and eventually was visible in the
day-time. Two years later, however, it disappeared, and has never since
been seen. In 1604 Kepler recorded a similar star in the constellation
of Ophiuchus which grew to be as bright as Jupiter. It also lasted for
about two years, and then faded away, leaving no trace behind. It is
rarely, however, that temporary stars attain to such a brilliance; and
so possibly in former times a number of them may have appeared, but not
have risen to a sufficient magnitude to attract attention. Even now,
unless such a star becomes clearly visible to the naked eye, it runs a
good chance of not being detected. A curious point, worth noting, with
regard to temporary stars is that the majority of them have appeared in
the Milky Way.

These sudden visitations have in our day received the name of _Novae_;
that is to say, "New" Stars. Two, in recent years, attracted a good deal
of attention. The first of these, known as Nova Aurigae, or the New Star
in the constellation of Auriga, was discovered by Dr. T.D. Anderson at
Edinburgh in January 1892. At its greatest brightness it attained to
about the fourth magnitude. By April it had sunk to the twelfth, but
during August it recovered to the ninth magnitude. After this last
flare-up it gradually faded away.

The startling suddenness with which temporary stars usually spring into
being is the groundwork upon which theories to account for their origin
have been erected. That numbers of dark stars, extinguished suns, so to
speak, may exist in space, there is a strong suspicion; and it is just
possible that we have an instance of one dark stellar body in the
companion of Algol. That such dark stars might be in rapid motion is
reasonable to assume from the already known movements of bright stars.
Two dark bodies mig