572 THE POPULAR SCIENCE MONTHLY. 



Yet, even at this stage of the inquiry, there were found minds bold 

 enough to question whether a perfectly satisfactory solution of the 

 great problem had really been attained. Nor is it difficult, I think, to 

 point out strong reasons for such doubts. I shall content myself by 

 naming one which has always appeared to me irresistible. 



The Orion nebula as seen in powerful telescopes covers a large ex- 

 tent of the celestial sphere. According to the Padre Secchi, who 

 observed it with the great Merz refractor of the observatory at Rome, 

 the nebulous region covers a triangular space, the width of whose base 

 is some eight times, while its height is more than ten times as great as 

 the moon's apparent diameter a space more than fifty times greater 

 than that covered by the moon. Now, I do not say that it is incon- 

 ceivable that an outlying star-system, so far off as to be irresolvable 

 by any but the most powerful telescopes, should cover so large a space 

 on the heavens. On the contrary, I do not believe that a galaxy re- 

 sembling our own would be resolvable at all, unless it were so near as 

 to appear much larger than the Orion nebula. I believe astronomers 

 have been wholly mistaken in considering any of the nebulas to be 

 such systems as our own. There may be millions of such systems in 

 space, but I am very certain no telescope we could make would suffice 

 to resolve any of them. But, what I do consider inconceivable is, that 

 a nebula extending so widely, and placed (as supposed) beyond our 

 system, should yet appear to cling (as the Orion nebula undoubtedly 

 does) around the fixed stars seen in the same field with it. So strongly 

 marked is this characteristic, that Sir John Herschel (who failed, ap- 

 parently, to see its meaning) mentions among others no less than four 

 stars one of which is the bright middle star of the belt as "involved 

 in strong nebulosity," while the intermediate nebulosity is only just 

 traceable. The probability that this arrangement is accidental is so 

 small as to be almost evanescent. However, as I have said, English as- 

 tronomers, almost without a dissentient voice, accepted the resolution 

 of the nebula as a proof that it represents a distant star-system resem- 

 bling our own galactic system, but far surpassing it in magnitude. 



The time came, however, when a new instrument, more telling even 

 than the telescope, was to be directed upon the Orion nebula, and with 

 very startling results. The spectroscope had revealed much respect- 

 ing the constitution of the fixed stars. We had learned that they are 

 suns resembling our own. It remained only to show that the Orion 

 nebula consists of similar suns, in order to establish beyond all possi- 

 bility of doubt the theories which had been so complacently accepted. 

 A very different result rewarded the attempt, however. When Dr. 

 Huggins turned his spectroscope toward the great nebula, he saw, in 

 place of a spectrum resembling the sun's, three bright lines only / A 

 spectrum of this sort indicates that the source of light is a luminous 

 gas, so that, whatever the Orion nebula may be, it is most certainly 

 not a congeries of suns resembling our own. 



