PROGRESS OF MODERN ASTRONOMY 



with electrical or phosphorescent light. Gravity event- 

 ually brings the nebular particles into closer aggrega- 

 tions, and increased collisions finally vaporize the entire 

 mass, forming planetary nebulae and gaseous stars. 

 Continued condensation may make the stellar mass 

 hotter and more luminous for a time, but eventually 

 leads to its liquefaction, and ultimate consolidation 

 the aforetime nebulae becoming in the end a dark or 

 planetary star. 



The exact correlation which Lockyer attempts to 

 point out between successive stages of meteoric con- 

 densation and the various types of observed stellar bod- 

 ies does not meet with unanimous acceptance. Mr. 

 Ranyard, for example, suggests that the visible nebulas 

 may not be nascent stars, but emanations from stars, 

 and that the true pre-stellar nebulae are invisible until 

 condensed to stellar proportions. But such details 

 aside, the broad general hypothesis that all the bodies 

 of the universe are, so to speak, of a single species 

 that nebulae (including comets), stars of all types, and 

 planets, are but varying stages in the life history of a 

 single race or type of cosmic organisms is accepted 

 by the dominant thought of our time as having the 

 highest warrant of scientific probability. 



All this, clearly, is but an amplification of that nebu- 

 lar hypothesis which, long before the spectroscope gave 

 us warrant to accurately judge our sidereal neighbors, 

 had boldly imagined the development of stars out of 

 nebulae and of planets out of stars. But Lockyer 's 

 hypothesis does not stop with this. Having traced the 

 developmental process from the nebular to the dark 

 star, it sees no cause to abandon this dark star to its 



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