e truly amazing. On four different
occasions he completed a survey of the firmament, and counted the stars
in several thousand gauge-fields; he discovered 2,400 nebulae, 800
double stars, and attempted to ascertain the approximate distances of
the stars by a comparison of their relative brightness.

It had long been surmised, though no actual proof was forthcoming, that
the law of gravitation by which the order and stability of our system
are maintained exercises its potent influence over other material bodies
existing in space, and that other systems, though differing in many
respects from that of ours, and presenting a more complex arrangement in
their structure, perform their motions subject to the guidance of this
universal law. The uncertainty with regard to the controlling influence
of gravity was removed by Herschel when he made his important discovery
of binary star systems. The components of a binary star are usually in
such close proximity that, to the naked eye, they appear as one star,
and sometimes, even with telescopic aid, it is impossible to distinguish
them individually; but when observed with sufficient magnifying power
they can be easily perceived as two lucid points. Double stars were for
a long time believed to be a purely optical phenomenon--an effect
created by two stars projected on the sphere so as to appear nearly in
the same line of vision, and, although apparently almost in contact,
situated at great distances apart. At one time Herschel entertained a
similar opinion with regard to those stars. In 1779 he undertook an
extensive exploration of the heavens with the object of discovering
double stars. As a result of his labours he presented to the Royal
Society in 1782 a list of 269 newly discovered double stars, and in
three years after he supplemented this list with another which contained
434 more new stars. He carefully measured the distances by which the
component stars were separated, and determined their position angles, in
order that he might be able to detect the existence of any sensible
parallax. On repeating his observations twenty years after, he
discovered that the relative positions of many of the stars had changed,
and in 1802 he made the important announcement of his discovery that the
components of many double stars form independent systems, held together
in a mutual bond of union and revolving round one common centre of
gravity.

The importance of this discovery, which we owe