Page:Popular Science Monthly Volume 3.djvu/588

572 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 extent 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 inconceivable 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 resembling 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, apparently, 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 astronomers, almost without a dissentient voice, accepted the resolution of the nebula as a proof that it represents a distant star-system resembling 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 respecting 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 possibility 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.