EVOLUTION AND THE SPECTROSCOPE. 323 



may be that a more careful study will show them to be gaseous, with 

 their spectral lines in a state of transition to the full continuous spec- 

 trum; but this is little more than bare conjecture at present ; for the 

 published descriptions of these' nebulae are too incomplete to admit of 

 very satisfactory discussion. 



This consideration of nebular spectra plunges us at once into a sea 

 of difficulties. We say that the sun and planets were formed by con- 

 densation and cooling from incandescent vapors, and hail the nebulae 

 as confirming this opinion. But could a sun be evoked, by cooling, 

 from a body less hot than itself? Moreover, the sun is known to con- 

 tain at least sixteen elements and probably many more. Were these 

 developed from a nebula containing only nitrogen and hydrogen ? Or 

 did the original nebulae differ in constitution ? All those which the 

 spectroscope has analyzed are chemically alike. We know nothing of 

 any whose constitution differs in this respect from theirs; and, there- 

 fore, if we point to them as confirmatory of the nebular hypothesis, we 

 are compelled to ask this portentous question : Did our planet, with 

 all its chemical complexity, arise, by a slow process of evolution, from 

 a glowing cloud of but two familiar gases ? Upon our answer to this 

 question depends largely the value of our spectroscopic confirmation 

 of the great hypothesis. The safety of the hypothesis itself is not in- 

 volved ; merely that of this one argument in its favor. We can easily 

 conceive of more complex nebulae, which could give rise to systems 

 like ours, although we know nothing of them. And, if we interpret the 

 spectra of some nebulae of the second class as due to gases at very high 

 temperature and pressure, the difficulty regarding the heat of our sun 

 will be easily gotten over. 



Let us consider the question suggested, as to the possible evolution 

 of complex from simple matter. It is easy to speak out boldly, in an 

 ex-cathedra manner, and say that an affirmative answer to such a ques- 

 tion would be absurd; but dogmatism of this sort is, in the highest 

 sense, unphilosophical and foolish. We do not know but that the 

 evolution of one element from another may be possible, under circum- 

 stances over which we have as yet no mastery ; indeed, such a view 

 would have many points of probability about it. Although unsup- 

 ported, it is quite strongly suggested by evidence. The demonstrated 

 unity of force leads us, by analogy, to expect a similar unity of mat- 

 ter ; and the many strange and hitherto unexplained relations between 

 the different elements tend to encourage our expectations. These ele- 

 ments, which seem to-day so diverse in character, may be, after all, one 

 in essence. This idea is philosophically strong, but waits for experi- 

 mental evidence to support it. At present, it can neither be discarded 

 as false, nor accepted as true. But what an addition the proof of such 

 a doctrine would bring to the philosophy of evolution ! 



Now, although questions like these cannot be settled by any evi- 

 dence which we are likely to obtain for many years to come, specula- 



