THE GREAT NEBULA IN ORION. 571 



our galaxy. Although Lord Rosse warned me that the circumstances 

 of the moment would not permit me to regard the decision then given 

 as absolutely final, I went in breathless interest to the inspection. Not 

 yet the veriest trace of a star! Unintelligible as ever, there the 

 nebula lay ; but how gorgeous its brighter parts 1 How countless 

 those streamers branching from it on every side ! How strange, espe- 

 cially that large horn on the north, rising in relief from the black 

 skies like a vast cumulous cloud ! It was thus still possible that the 

 nebula was irresolvable by human art ; and so doubt remained. Why 

 the concurrence of every favorable condition is requisite for success in 

 such inquiries may be readily comprehended. The object in view is 

 to discern, singly, sparkling points, small as the point of a needle, and 

 close as the particles of a handful of sand ; so that it needs but the 

 smallest unsteadiness in the air, or imperfection in the shape of the 

 reflecting surface, to scatter the light of each point, to merge them 

 into each other, and present them as one mass." 



Before long, Lord Rosse, after regrinding the great mirror, obtained 

 better views of the mysterious nebula. Even now, however, he could 

 use but half the power of the telescope, yet at length the doubts of 

 astronomers as to the resolvability of the nebula were removed. " We 

 could plainly see," he wrote to Prof. Nichol, " that all about the tra- 

 pezium was a mass of stars, the rest of the nebula also abounding 

 with stars, and exhibiting the characteristics of resolvability strongly 

 marked." These views were abundantly confirmed by subsequent ob- 

 servations with the great mirror. 



It will surprise many to learn that even Lord Rosse's great reflector 

 is surpassed in certain respects by some of the exquisite refractors now 

 constructed by opticians. As a light-gatherer the mirror is, of course, 

 unapproachable by refractors. Even if it were possible to construct 

 an achromatic lens six feet in diameter, yet, to prevent flexure, a thick- 

 ness would have to be given to the glass which would render it almost 

 impervious to light, and therefore utterly useless. But refractors have 

 a power of definition not possessed by large reflectors. With a re- 

 fractor eight inches only in aperture, for instance, Mr. Dawes has 

 obtained better views of the planets (and specially of Mars) than 

 Lord Rosse's six-feet speculum would give under the most favorable 

 circumstances. And, in like manner, the performance of Lord Rosse's 

 telescope on the Orion nebula has been surpassed so far as resolution 

 into discrete stars is concerned by the exquisite defining power of 

 the noble refractor of Harvard College (U. S.). By means of this in- 

 strument, hundreds of stars have been counted within the confines of 

 the once intractable nebula. 



It seemed, therefore, that all doubt had vanished from the subject 

 which had so long perplexed astronomers. " That was proved to be 

 real" Nichol wrote, " which, with conceptions of space enlarged even 

 as Herschel's, we deemed incomprehensible." 



