EVOLUTION AND THE SPECTROSCOPE. 321 



respects been more than doubled. Problems which were deemed in- 

 soluble, have been settled with the greatest ease. The magnitude of 

 the discoveries already made leads us to expect still greater revelations 

 in the future. Let us see what the spectroscope has to say for the 

 philosophy of evolution. 



Among the doctrines held by evolutionists, the all but proved 

 Nebular Hypothesis occupies a very prominent position. Originating 

 with Kant more than a century ago, and afterward furnished with 

 secure foundations by Laplace, it has since striven for complete ac- 

 ceptance with ever-varying strength. According to this hypothesis, 

 our solar system began existence as a nebulous cloud of incandescent 

 vapor, which, rotating about a centre, and cooling as it revolved, cast 

 off rings of matter that gathered into globes and became planets, while 

 the central portion, undergoing less change, formed the sun. A vast 

 weight of physical and mathematical evidence supported this theory, 

 and the. nebulae seen in different parts of the heavens lent to it the 

 confirmation of analogy. From the first, the hypothesis was strong. 



But soon doubts began to arise. Larger and more powerful tele- 

 scopes were constructed, and many nebulas were resolved into clusters 

 of stars. Astronomers began- to hope that all these bodies might be 

 similarly resolved, and the nebular hypothesis lost a little ground. 

 But the spectroscope came apparently to the rescue. In the skilful 

 hands of Mr. Hoggins, the narrow slit was made to receive the light 

 of several unresolved nebulas, and nebula after nebula gave up its 

 secret to the observer. Some yielded spectra, consisting of from one 

 to four bright lines, while others gave continuous bands of feeble light. 

 The former class told the story. Spectra like theirs could belong only 

 to the light emitted by incandescent gas, and therefore of such material, 

 true nebulous vapor, these distant bodies consisted. But even more 

 was revealed. The bright lines were characteristic of two well-known 

 substances, nitrogen being the more distinct of the two, and hydrogen 

 the less clearly visible. No other elements could be detected, nor 

 could any good reason be found for supposing others to be present. 

 But the main fact of the existence of genuine nebulas was fairly de- 

 monstrated, and the nebular hypothesis received a great accession of 

 strength. To-day it almost commands acceptance, although it is 

 capable of being made much stronger. Even the evidence which 

 analogy might offer in its favor is far from complete. We must look 

 to the spectroscope for its completion. 



In this connection a great variety of interesting questions suggest 

 themselves. We assume that our planet originated from a gaseous 

 cloud by a slow process of condensation and cooling, and point to the 

 visible nebulas to confirm our views. Now, in evolving a solar system 

 from a nebula, a long series of changes would necessarily occur. We 

 see the extremes of such a line of development, and also a few of the 

 intermediate links. And we are at once led to ask whether we can 



VOL. II. 21 



