THE GREAT NEBULA IN ORION. 569 



vindicated Herschel's claim to be looked upon as the most clear- 

 sighted, as well as the boldest and most original, of astronomical 

 theorizers. 



Herschel had pointed out various circumstances which, in his opin- 

 ion, justified a belief in the existence of a nebulous substance fire- 

 mist or star-mist, as it has been termed throughout interstellar space. 

 He had discovered and observed several thousand nebulce, and he con- 

 sidered that among these he could detect traces of progressive devel- 

 opment. Some nebulae were, he supposed, comparatively young ; they 

 showed no signs of systematic aggregation or of central condensation. 

 In some nebulae he traced the approach toward the formation of subor- 

 dinate centres of attraction; while in others, again, a single centre 

 began to be noticeable. He showed the various steps by which ag- 

 gregation of the former kind might be supposed to result in the for- 

 mation of star-clusters, and condensation of the latter kind into the 

 formation of conspicuous single stars. 



But it was felt that the strongest part of Herschel's case lay in his 

 reference to the great nebula of Orion. He pointed out that, among 

 all the nebulas which might be reasonably assumed to be star-systems, 

 a certain proportionality had always been found to exist between the 

 telescope which first detected a nebula and that which effected its 

 resolution into stars. And this was what might be expected to hap- 

 pen with star-systems lying beyond our galactic system. But how 

 different is this from what was seen in the case of the Orion nebula ! 

 Here is an object so brilliant as to be visible to the naked eye, and 

 which is found, on examination, to cover a large region of the heavens. 

 And yet the most powerful telescopes had failed to show the slightest 

 symptom of resolution. Were we to believe that we saw here a sys- 

 tem of suns so far off that no telescope could exhibit the separate ex- 

 istence of the component luminaries, and therefore (considering merely 

 the observed extent of the nebula, which is undoubtedly but a faint 

 indication of its real dimensions) so inconceivably enormous in extent 

 that the star-system of which our sun is a member shrinks into noth- 

 ingness in comparison ? Surely it seemed far more reasonable to rec- 

 ognize in the Orion nebula but a portion of our galaxy a portion 

 very vast in extent, but far inferior to that " limitless ocean of uni- 

 verses " presented to us by the other view. 



And when Sir W. Herschel was able, as he thought, to point to 

 changes taking place within the Orion nebula, it seemed yet more im- 

 probable that the object was a star-system. 



But now telescopes more powerful than those with which the elder 

 Herschel had scanned the great nebula were directed to its examina- 

 tion. Sir John Herschel, following in his father's footsteps, applied 

 himself to the diligent survey of the marvellous nebula with a reflect- 

 ing telescope 18 inches in aperture. He presented the nebula to us as 

 an object of which " the revelation of the 10-feet telescope was but the 



