larger views of the nature and extent of the nebulous
matter itself.

His views on the nature of nebulae underwent successive changes. At first
he supposed all nebulae to be but aggregations of stars. The logic was
simple. To the naked eye there are many groups of stars which appear
nebulous. _Praesepe_ is, perhaps, the best example. The slightest
telescopic power applied to such groups alters the nebulous appearance,
and shows that it comes from the combined and confused light of discrete
stars. Other groups which remain nebulous in a seven-foot telescope,
become stellar in a ten-foot. The nebulosity of the ten-foot can be
resolved into stars by the twenty-foot, and so on. The nebulae which
remained still unresolved, it was reasonable to conclude, would yield to
higher power, and generally a nebula was but a group of stars removed to
a great distance. An increase of telescopic power was alone necessary to
demonstrate this.[37]

"Nebulae can be selected so that an insensible gradation shall take
place from a coarse cluster like the _Pleiades_ down to a milky
nebulosity like that in _Orion_, every intermediate step being
represented. This tends to confirm the hypothesis that all are
composed of stars more or less remote."

So, at first, HERSCHEL believed that his twenty-foot telescope was of
power sufficient to fathom the Milky Way, that is, to see through it and
beyond it, and to reduce all its nebulosities to true groups of stars.

In 1791 he published a memoir on _Nebulous Stars_, in which his views
were completely changed. He had found a nebulous star, the sixty-ninth
of his Class IV., to which his reasons would not apply. In the centre of
it was a bright star; around the star was a halo gradually diminishing
in brightness from the star outward, and perfectly circular. It was
clear the two parts, star and nebula, were connected, and thus at the
same distance from us.

There were two possible solutions only. Either the whole mass was,
_first_, composed of stars, in which case the nucleus would be
enormously larger than the other stars of its stellar magnitude
elsewhere in the sky, or the stars which made up the halo indefinitely
small; or, _second_, the central nucleus was indeed a star, but a star
surrounded with "a shining fluid, of a nature totally unknown to us."

The long strata of nebulae, which he had before described under the name
of "telescopic Milky Ways," might well be accounted f