will eventually become of the ``runaways.'' Without a collision, or a
series of very close approaches to great gravitational centers, a star
traveling through space at the rate of two hundred or three hundred
miles per second could not be arrested or turned into an orbit which
would keep it forever flying within the limits of the visible
universe. A famous example of these speeding stars is ``1830
Groombridge,'' a star of only the sixth magnitude, and consequently
just visible to the naked eye, whose motion across the line of sight
is so rapid that it moves upon the face of the sky a distance equal to
the apparent diameter of the moon every 280 years. The distance of
this star is at least 200,000,000,000,000 miles, and may be two or
three times greater, so that its actual speed cannot be less than two
hundred, and may be as much as four hundred, miles per second. It
could be turned into a new course by a close approach to a great sun,
but it could only be stopped by collision, head-on, with a body of
enormous mass. Barring such accidents it must, as far as we can see,
keep on until it has traversed our stellar system, whence in may
escape and pass out into space beyond, to join, perhaps, one of those
other universes of which we have spoken. Arcturus, one of the greatest
suns in the universe, is also a runaway, whose speed of flight has
been estimated all the way from fifty to two hundred miles per second.
Arcturus, we have every reason to believe, possesses hundreds of times
the mass of our sun -- think, then, of the prodigious momentum that
its motion implies! Sirius moves more moderately, its motion across
the line of sight amounting to only ten miles per second, but it is at
the same time approaching the sun at about the same speed, its actual
velocity in space being the resultant of the two displacements.

What has been said about the motion of Sirius brings us to another
aspect of this subject. The fact is, that in every case of stellar