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SCIENCE 



[N. S. Vol. XLV. No. 1169 



evidence that the catastrophes which pro- 

 duce new or temporary stars produce tem- 

 porary nebulffi, for at a certain stage of 

 their existence the temporary stars have 

 nebular spectra; but in all cases thus far 

 observed — as Adams has shown — the nebu- 

 lar spectrum quickly transforms itself into 

 the Wolf-Rayet stellar spectrum. It is not 

 impossible that the planetary nebulae have 

 in some cases resulted from the more vio- 

 lent catastrophes of distant space and 

 time ; that bodies originally stars may have 

 been expanded under the heat of collision 

 or other catastrophe to nebular conditions ; 

 but that an viltimate condensation will 

 transform such uebulfe again into the 



stellar state, we can not doubt. That such 

 nebulffi as those in the Pleiades (Fig. 13) or 

 as the great Net-Work nebula in Cygnus 

 (Fig. 36) were formed from stars can not 

 be regarded with favor for a moment ; but 

 that the many Class B stars existing in 

 those regions should have been formed from 

 nebulous matter, and that others may be 

 forming, implies an evolutionary process 

 that is both natural and easy of comprehen- 

 sion. Transformation from star to nebula 

 is abnormal, is reiioluti-on, under the influ- 

 ence of catastrophe. Transformation from 

 nebula to star is normal, is et^olution, under 

 the continuous and regular operation of the 

 simple laws of physics. 



The Net-work Nebula in Cygnus, photographed by Keeler with the 

 Crossley Eeflector of the Lick Observatory. 



