stars that are visible to the naked eye, Herschel sees
series after series of more distant stars, marshalled in
galaxies of millions; but at last he reaches a distance
beyond which the galaxies no longer increase. And
yet--so he thinks--he has not reached the limits of his
vision. What then? He has come to the bounds of the
sidereal system--seen to the confines of the universe.
He believes that he can outline this system, this universe,
and prove that it has the shape of an irregular
globe, oblately flattened to almost disklike proportions,
and divided at one edge--a bifurcation that is revealed
even to the naked eye in the forking of the Milky Way.

This, then, is our universe as Herschel conceives it--
a vast galaxy of suns, held to one centre, revolving,
poised in space. But even here those marvellous telescopes
do not pause. Far, far out beyond the confines
of our universe, so far that the awful span of our own
system might serve as a unit of measure, are revealed
other systems, other universes, like our own, each composed,
as he thinks, of myriads of suns, clustered like
our galaxy into an isolated system--mere islands of
matter in an infinite ocean of space. So distant from
our universe are these now universes of Herschel's discovery
that their light reaches us only as a dim, nebulous
glow, in most cases invisible to the unaided eye.
About a hundred of these nebulae were known when
Herschel began his studies. Before the close of the
century he had discovered about two thousand more of
them, and many of these had been resolved by his