stretches of sidereal space. Were the comet which hurtles
past us at a speed of, say, a hundred miles a second to continue its
mad flight unchecked straight into the void of space, it must fly on its
frigid way eight thousand years before it could reach the very nearest
of our neighbor stars; and even then it would have penetrated but a
mere arm's-length into the vistas where lie the dozen or so of sidereal
residents that are next beyond. Even to the trained mind such distances
are only vaguely imaginable. Yet the astronomer of our century has
reached out across this 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 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