HERSCHEL THE DISCOVERER. 33 



nature. We therefore either have a central body 

 which is not a star, or have a star which is 

 involved in a shining fluid, of a nature totally 

 unknown to us." And with caution he added 

 that " the envelope of a cloudy star is more fit 

 to produce a star by its condensation than to 

 depend upon the star for its existence." 



This was written in 1791, five years before 

 Laplace propounded his nebular theory. Mean- 

 while Herschel, believing that " these nebulous 

 stars may serve as a clue to unravel other 

 mysterious phenomena, found that the theory 

 of a " shining fluid " would suit the appear- 

 ance of the irresolvable planetary nebulae and 

 the great nebula in Orion much better than 

 the extravagant idea of "external universes." 

 Herschel now considered the Orion nebula to 

 be much nearer to the Solar System than he 

 formerly did, and ceased to regard it as ex- 

 ternal to the Galaxy. For twenty years Herschel 

 patiently observed the nebulae, and it was not 

 until 1811 that he propounded his nebular hypo- 

 thesis of the evolution of the Sun and stars. 

 He found the gaseous matter in all stages of 

 condensation, from the diffused cloudy nebulae 

 like that in Orion, through the planetary nebula 

 and the regular nebula, to the perfect stars, like 

 Sirius and the Sun. Herschel's nebular theory 



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