distance) causes the stars to appear confused to
our unassisted eye.

At one time, the results achieved by Lord
Rosse's gigantic telescope, gave rise to expectations
that all the nebulæ might be resolved. It
was confidently asserted that if any doubt was
still entertained respecting their resolvability,
that doubt was very small indeed. At a later
period, nevertheless, Lord Rosse had not yet
completely succeeded in resolving the whole of
Orion's nebula; he expressed his hopes of being
able to do so, and that was all. In spite of
similar efforts made by other astronomers, there
still remain nearly four thousand unresolved
nebulæ; that is, nebulæ in which it has not
been possible to ascertain the existence of
distinct luminous bodies—of stars, in short.

Two hypotheses have been started about the
nebulæ. One assumes them to be clusters of
stars, so distant that their light becomes
confused into a faint blot or blur, which only
requires instruments of sufficient power to show
the separate stars of which it is composed.
Each nebula was taken to be a little, or rather
a partial universe, complete in itself. This
theory, originally held by Galileo and Cassini,
has Lord Rosse, Herschel, and others, amongst
its modern supporters.

Other not less illustrious astronomers, as
Halley, Kepler, and Tyco Brahe, have
maintained that true nebulæ do not consist of stars.
It is assumed that there exist in the heavenly
spaces luminous masses of cloudy matter, which,
by slow and gradual condensation, ultimately
become stars. According to this theory, the
impossibility of resolving certain nebulæ is
owing, not to the weakness of our telescopes,
but to the very nature of the object viewed.
The well-ascertained variations of the forms and
dimensions of certain nebulæ, the assurance
acquired by science that there exist heavenly
bodies of all dimensions and all densities, the
excessively slight density of the comets, and
the known laws of attraction, are so many
presumptions which argue in favour of this second
hypothesis. Its extreme probability has been
further confirmed by the application of the
spectral analysis.

It was a bold idea for weak and ephemeral
man to investigate the nature of bodies outlying
on the uttermost verge of visible space, and
belonging to long-expired epochs of time. These
nebulæ, whose light is now being analysed—
these stars in which we have ascertained the
presence of a number of earthly elements—may
have been extinguished, perhaps, for thousands
of years, or may have gone to illuminate other
regions of the heavens. In consequence of their
prodigious distance, and the time their light
requires to reach us, we may see them here after
they have ceased to shine. Sight thus carries
us back into periods of distant time, just as it
conveys us forward into regions of distant space.
We see distinctly, with our own living eyes,
what was happening ages ago. The stars are
for us, according to Humboldt's expression, the
voices of the past wafted back to us.

In November last, Mr. Huggins read before
the Royal Society an account of his experiments
on the light of the nebulæ. Spectral analysis
had already taught us that, with the exception
of a few trifling differences, a great number of
the fixed stars possess a physical constitution
identical with that of the sun. Consequently,
prismatic observation would appear to be the
best means of determining whether there exist
any essential difference between the fixed stars
and the nebulæ—either in the nature of the
matters composing them, or in the conditions
under which their light is emitted. In short,
this ingenious method promised to resolve the
problem whether the structure of the nebulæ is
comparable to that of planets and stars; or
whether they are mere vapour without any
nucleus or denser consistency, and composed
solely of cosmic matter of excessively feeble
density.

This is scarcely the place to describe the
arrangement of Mr. Muggins's optical apparatus.
He selected for examination the nebulæ which
offer small round or elliptical disks, and which
Sir John Herschel classed as planetary nebulæ.
There is little probability of their being
resolvable. Their colour is green, and sometimes
blue, and they present no sign of central
condensation. The first examined was a nebula of
the Dragon. Its light, unlike that of all other
extra-terrestrial bodies, is not composed of rays
having different degrees of refrangibility, and
therefore does not form a spectrum. It is in
great part monochromatic—that is, of one single
colour; and after passing through the prism, it
remains concentrated in one brilliant line. Careful
examination discovered, besides, a second
bright line separated from the first by a dark
interval; and afterwards, a third bright line,
but much fainter than the other two. The
position of the first corresponds to azote; that
of the second to hydrogen; the third appears to
belong to some unknown element. It is close
to one of the brilliant stripes observed in the
spectrum of baryum.

In the majority of the other nebulæ examined,
the three bright rays have been seen in the same
position; in some few, a fourth stripe has been
remarked.

Such nebulæ, our astronomer believes, can no
longer be regarded as clusters of suns resembling
our sun and the fixed stars in their constitution,
but as stars or astral bodies of a distinct form
and peculiar constitution. Instead of being
incandescent bodies, in a solid or a liquid state,
transmitting light of various refrangibilities
through an atmosphere which intercepts a
certain number of rays—which appears to be
the constitution of our sun—they (or at least
their luminous surface) ought probably to be
considered as enormous masses of gas or luminous
vapour. As far as we know, it is only by matter
in a gaseous state that light can be emitted,
having so limited a degree of refrangibility. The
extreme simplicity of the structure of one of
these nebulæ is indicated by the three bright
stripes, if we regard them, as denoting the