all instruments but his own, so Lord Rosse's even
greater reflector resolved others that would not yield to
Herschel's largest mirror. It seemed a fair inference
that with sufficient power, perhaps some day to be attained,
all nebulae would yield, hence that all are in
reality what Herschel had at first thought them--
vastly distant "island universes," composed of aggregations
of stars, comparable to our own galactic system.

But the inference was wrong; for when the spectroscope
was first applied to a nebula in 1864, by Dr. Huggins,
it clearly showed the spectrum not of discrete
stars, but of a great mass of glowing gases, hydrogen
among others. More extended studies showed, it is
true, that some nebulae give the continuous spectrum
of solids or liquids, but the different types intermingle
and grade into one another. Also, the closest affinity
is shown between nebulae and stars. Some nebulae are
found to contain stars, singly or in groups, in their
actual midst; certain condensed "planetary" nebulae
are scarcely to be distinguished from stars of the gaseous
type; and recently the photographic film has
shown the presence of nebulous matter about stars
that to telescopic vision differ in no respect from the
generality of their fellows in the galaxy. The familiar
stars of the Pleiades cluster, for example, appear on the
negative immersed in a hazy blur of light. All in all,
the accumulated impressions of the photographic film
reveal a prodigality of nebulous matter in the stellar
system not hitherto even conjectured.