hesitating belief in the existence of phosphorescent matter,
"disseminated through extensive regions of space in the manner of a
cloud or fog,"[120] was changed into a conviction that no valid
distinction could be established between the faintest wisp of cosmical
vapour just discernible in a powerful telescope, and the most brilliant
and obvious cluster. He admitted, however, an immense range of possible
variety in the size and mode of aggregation of the stellar constituents
of various nebulae. Some might appear nebulous from the closeness of
their parts; some from their smallness. Others, he suggested, might be
formed of "discrete luminous bodies floating in a non-luminous
medium;"[121] while the annular kind probably consisted of "hollow
shells of stars."[122] That a physical, and not merely an optical,
connection unites nebulae with the _embroidery_ (so to speak) of small
stars with which they are in many instances profusely decorated, was
evident to him, as it must be to all who look as closely and see as
clearly as he did. His description of No. 2,093 in his northern
catalogue as "a network or tracery of nebula following the lines of a
similar network of stars,"[123] would alone suffice to dispel the idea
of accidental scattering; and many other examples of a like import might
be quoted. The remarkably frequent occurrence of one or more minute
stars in the close vicinity of "planetary" nebulae led him to infer their
dependent condition; and he advised the maintenance of a strict watch
for evidences of circulatory movements, not only over these supposed
stellar satellites, but also over the numerous "double nebulae," in
which, as he pointed out, "all the varieties of double stars as to
distance, position, and relative brightness, have their counterparts."
He, moreover, investigated the subject of nebular distribution by the
simple and effectual method of graphic delineation or "charting," and
succeeded in showing that while a much greater uniformity of scattering
prevails in the southern than in the northern heavens, a condensation is
nevertheless perceptible about the constellations Pisces and Cetus,
roughly corresponding to the "nebular region" in Virgo by its vicinity
(within 20 deg. or 30 deg.) to the opposite pole of the Milky Way. He
concluded "that the nebulous system is distinct from the sidereal, though
involving, and perhaps to a certain extent intermixed with, the
latter."[124]

Towards the close of his