322 
POPULAR SCIENCE REVIEW. 
that in the nebulae resolvable^ and yet unresolved, we have 
evidence of the gradual coalescence of matter into worlds. 
Humboldt supposes that if all the discovered nebulae — ^being 
on the outermost and remotest strata of self-luminous worlds — 
known to us now were resolved into stars, the mechanical 
improvements in progress will eventually so increase the power 
of our instruments, that nebulae yet more remote will be dis- 
covered to us. We have endeavoured to show that we have 
evidence to prove that the stars and planets are, all of them, 
constituted of matter similar to that existing in the Sun, and 
that solar matter and terrestrial matter are chemically alike. 
It is most probable, as we have also said, that the elements 
may vary in those distinct worlds ; and hence the physical 
differences which we detect. But it is obvious that the nebulge 
can no longer be regarded as aggregations of stars, after the 
order to which our own Sun and the fixed stars belong. We 
have,’’^ writes Mr. W. Huggins, ‘^^in these objects, to do no 
longer with a special modification only of our own type of 
suns, but we find ourselves in the presence of objects possess- 
ing a distinct and peculiar plan of structure. In place of an 
incandescent solid or liquid body transmitting light of all 
refrangibilities through an atmosphere which intercepts by 
absorption a certain number of them, such as our Sun appears 
to be, we must probably regard these objects, or at least their 
photo-surfaces, as enormous masses of luminous gas or vapour.'’^ 
As we advance in our discoveries, it not unfrequently happens 
that we are led back to the speculations of some older thinker ; 
and the discoveries made by Mr. Huggins rather confirm the 
views which were entertained by Halley — that the nebulae are 
^‘"a gaseous and elementary form of luminous sidereal matter.^"’ 
In the drawing which we have copied (fig. 6), it will appear 
that a line of faint light has been marked as corresponding 
with the hydrogen line, and that the line of bright light agrees 
with nitrogen. Mr. Huggins, with the caution of a true philo- 
sopher, expresses himself so guardedly and so well respecting 
those lines, that we cannot refrain from quoting his own 
words : — 
Another consideration which opposes the notion that these nebulee are 
clusters of stars, is found in the extreme simplicity of constitution which the 
three bright lines suggest, as indicating the presence of nitrogen, hydrogen, 
and a substance unknown. It is perhaps of importance to state that, except 
nitrogen, no one of thirty of the chemical elements, the spectra of which 
I have measured, has a strong line very near the bright line of the nebulae. 
If, however, this line were due to nitrogen, we ought to see other lines as 
well ; for there are specially two strong double lines in the spectrum of 
nitrogen, one at least of which, if they existed in the light of the nebulae, 
would be easily visible The speculation presents itself, whether the 
