him, his first extended work was the observation of his
father's double stars. His studies, in which at first he
had the collaboration of Mr. James South, brought to
light scores of hitherto unrecognized pairs, and gave
fresh data for the calculation of the orbits of those
longer known. So also did the independent researches
of F. G. W. Struve, the enthusiastic observer of the
famous Russian observatory at the university of Dorpat,
and subsequently at Pulkowa. Utilizing data
gathered by these observers, M. Savary, of Paris,
showed, in 1827, that the observed elliptical orbits of
the double stars are explicable by the ordinary laws of
gravitation, thus confirming the assumption that Newton's
laws apply to these sidereal bodies. Henceforth
there could be no reason to doubt that the same force
which holds terrestrial objects on our globe pulls at
each and every particle of matter throughout the visible
universe.

The pioneer explorers of the double stars early found
that the systems into which the stars are linked are by
no means confined to single pairs. Often three or four
stars are found thus closely connected into gravitation
systems; indeed, there are all gradations between binary
systems and great clusters containing hundreds or
even thousands of members. It is known, for example,
that the familiar cluster of the Pleiades is not merely
an optical grouping, as was formerly supposed, but an
actual federation of associated stars, some two thousand
five hundred in number, only a few of which are