A HISTORY OF SCIENCE 



And these vast clouds of world-stuff have been found 

 by Professor Keeler, of the Lick observatory, to be 

 floating through space at the starlike speed of from 

 ten to thirty-eight miles per second. 



The linking of nebulae with stars, so clearly evi- 

 denced by all these modern observations, is, after all, 

 only the scientific corroboration of what the elder Her- 

 schel's later theories affirmed. But the nebulas have 

 other affinities not until recently suspected; for the 

 spectra of some of them are practically identical with 

 the spectra of certain comets. The conclusion seems 

 warranted that comets are in point of fact minor nebu- 

 lae that are drawn into our system ; or, putting it other- 

 wise, that the telescopic nebulae are simply gigantic 

 distant comets. 



Lockyer's Meteoric Hypothesis 



Following up the surprising clews thus suggested, 

 Sir Norman Lockyer, of London, has in recent years 

 elaborated what is perhaps the most comprehensive 

 cosmogonic guess that has ever been attempted. His 

 theory, known as the "meteoric hypothesis," probably 

 bears the same relation to the speculative thought of 

 our time that the nebular hypothesis of Laplace bore 

 to that of the eighteenth century. Outlined in a few 

 words, it is an attempt to explain all the major phe- 

 nomena of the universe as due, directly or indirectly, to 

 the gravitational impact of such meteoric particles, or 

 specks of cosmic dust, as comets are composed of. Neb- 

 ulae are vast cometary clouds, with particles more or 

 less widely separated, giving off gases through meteoric 

 collisions, internal or external, and perhaps glowing also 



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