THE SPECTRA OE SOME OF THE FIXED STARS. 
433 
These stars are without exception feeble in the intensity of their light. The expla- 
nation is not admissible, that the faint blue or violet light is due to a less intense 
incandescence of the radiating surface, since it is precisely these more refrangible rays 
which would be the first to fail as the temperature diminished, and upon this supposi- 
tion the star should be dull red. It is of course to be supposed that in the process of 
gradual cooling some bodies which are less volatile than others would cease to exist in 
the atmosphere at an earlier period than others, or that they might enter into new 
combinations more readily than others, and so modify the tint of the light emitted. 
The existence around these blue stars of an extended atmosphere of “fog” will not 
explain the absorption of the less refrangible portion of the luminous spectrum. 
21. These spectrum observations are not without interest also when viewed in con- 
nexion with the nebular hypothesis of the cosmical origin of the solar system and fixed 
stars. For if it be supposed that all the countless suns which are distributed through 
space, or at least those of them which are bright to us, were once existing in the con- 
dition of nebulous matter, it is obvious that, though certain constituents may have 
been diffused throughout its mass, yet the composition of the nebulous material must 
have differed at different points ; otherwise, during the act of agglomeration, each 
system must have collected and condensed equal proportions of similar materials from 
the mass around. It cannot be supposed that similarity in physical properties has caused 
the association of the different elements : we find, for example, some of the least volatile 
of the metals, such as iron, associated with highly volatile elements, such as mercury 
and tellurium, in the same star. 
If we may so say, there seems to be some analogy between this irregular distribution 
of the elements in different centres in space, and the manner in which the components 
of the earth’s crust are distributed. Upon the earth there are certain very generally 
diffused elements, such as oxygen, hydrogen, carbon, silicon, iron, aluminium, and 
calcium, which occur in all parts ; whilst there are others which, like silver, tin, lead, 
and other metals, are accumulated at particular points only. Whatever may have been 
the physical causes which may have produced this separation, we see abundant evidence 
of the advantage of this distribution in their application to the purposes of man — small- 
ness in relative amount being compensated for by the accumulation of the material in 
denser deposits, which allow of their comparatively easy extraction to supply the wants 
of mankind. If this arrangement be admitted as designed in the case of the earth, is it 
going beyond the limits of fair deduction to suppose that, were we acquainted with the 
economy of those distant globes, an equally obvious purpose might be assigned for the 
differences in composition which they exhibit \ 
22. The additional knowledge which these spectrum observations give us of the nature 
and of the structure of the fixed stars, seems to furnish a basis for some legitimate specu- 
lation in reference to the great plan of the visible universe, and to the special object and 
design of those numerous and immensely distant orbs of light. 
The closely marked connexion, in similarity of plan and mode of operation, in those 
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