in the Catalogue of 1782 alone, and many
thousands are now known.

By a process like this, HERSCHEL reached his grand discovery of true
binary systems, where one sun revolves about another. For he saw that
if the two stars are near together in space, they could not stand still
in face of each other, but that they must revolve in true orbits. Here
was the discovery which came to take the place of the detection of the
parallaxes of the fixed stars.

He had failed in one research, but he was led to grand conclusions.
Was the force that these distant pairs of suns obeyed, the force of
gravitation? This he could not settle, but his successors have done so.
It was not till about 1827 that SAVARY, of the Paris Observatory, showed
that one of HERSCHEL'S doubles was subjected to the law of gravitation,
and thus extended the power of this law from our system to the universe
at large. HERSCHEL himself lived to see some of his double stars perform
half a revolution.

Of HERSCHEL'S discoveries, ARAGO thinks this has "le plus d'avenir."
It may well be so. The laws which govern our solar system have been
extended, through his researches, to regions of unknown distance. The
binary stars will afford the largest field for research into the laws
which govern them, and together with the clusters and groups, they will
give a firm basis by which to study the distribution of stars in
general, since here we have the great advantage of knowing, if not the
real distance of the two stars from the earth, at least that this
distance is alike for both.

_Researches on Planets and Satellites._

After HERSCHEL'S first publication on the mountains of the Moon (1780),
our satellite appears to have occupied him but little. The observation
of volcanoes (1787) and of a lunar eclipse are his only published ones.
The planets _Mercury_, _Venus_, _Mars_, and _Jupiter_, although they
were often studied, were not the subjects of his more important memoirs.
The planet _Saturn_, on the contrary, seems never to have been lost
sight of from the time of his first view of it in 1772.

The field of discovery always appears to be completely occupied until
the advent of a great man, who, even by his way of putting old and
familiar facts, shows the paths along which discoveries must come, if at
all. This faculty comes from profound reflection on the nature of the
subject itself, from a sort of transmuting power which changes the words
of the boo