unthinkable void and brought back many a secret
which our predecessors thought forever beyond human
grasp.

A tentative assault upon this stronghold of the stars
was being made by Herschel at the beginning of the
century. In 1802 that greatest of observing astronomers
announced to the Royal Society his discovery that
certain double stars had changed their relative positions
towards one another since he first carefully charted
them twenty years before. Hitherto it had been supposed
that double stars were mere optical effects. Now
it became clear that some of them, at any rate, are
true "binary systems," linked together presumably by
gravitation and revolving about one another. Halley
had shown, three-quarters of a century before, that the
stars have an actual or "proper" motion in space;
Herschel himself had proved that the sun shares this
motion with the other stars. Here was another shift
of place, hitherto quite unsuspected, to be reckoned
with by the astronomer in fathoming sidereal secrets.


Double Stars

When John Herschel, the only son and the worthy
successor of the great astronomer, began star-gazing in
earnest, after graduating senior wrangler at Cambridge,
and making two or three tentative professional starts in
other directions to which his versatile genius impelled