The whole question of star-drift has lately assumed a new phase, in
consequence of the investigations of Kapteyn, Dyson, and Eddington on
the ``systematic motions of the stars.'' This research will, it is
hoped, lead to an understanding of the general law governing the
movements of the whole body of stars constituting the visible
universe. Taking about eleven hundred stars whose proper motions have
been ascertained with an approach to certainty, and which are
distributed in all parts of the sky, it has been shown that there
exists an apparent double drift, in two independent streams, moving in
different and nearly opposed directions. The apex of the motion of
what is called ``Stream I'' is situated, according to Professor
Kapteyn, in right ascension 85°, declination south 11°, which places
it just south of the constellation Orion; while the apex of ``Stream
II'' is in right ascension 260°, declination south 48°, placing it in
the constellation Ara, south of Scorpio. The two apices differ very
nearly 180° in right ascension and about 120° in declination. The
discovery of these vast star-streams, if they really exist, is one of
the most extraordinary in modern astronomy. It offers the correlation
of stellar movements needed as the basis of a theory of those
movements, but it seems far from revealing a physical cause for them.
As projected against the celestial sphere the stars forming the two
opposite streams appear intermingled, some obeying one tendency and
some the other. As Professor Dyson has said, the hypothesis of this
double movement is of a revolutionary character, and calls for further
investigation. Indeed, it seems at first glance not less surprising
than would be the observation that in a snow-storm the flakes over our
heads were divided into two parties and driving across each other's
course in nearly opposite directions, as if urged by interpenetrating
winds.