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Page:Popular Science Monthly Volume 38.djvu/354

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THE POPULAR SCIENCE MONTHLY.

of the geometrical arrangement of the former. So with the chain of telescopic stars described above as winding around the bright stars in the Belt—the nebular forms account for the configuration of the stars.

In the cut of Orion's Belt, above, an attempt has been made to represent the appearance of the assemblage of small stars around Epsilon, the center star of the Belt. All the stars there shown can not be seen with an ordinary opera-glass, but a strong field-glass will reveal them and many more besides. In fact, with a powerful glass the complication of curving star-lines becomes rather confusing to one attempting to draw them, and the cut must be regarded rather as an "impressionist" picture than as one showing every star accurately in its place and of precisely the right magnitude. Still, it will be found an approximately correct representation. The reader should bear in mind the fact that the star Epsilon, the center of this remarkable sidereal array, has long been known to be surrounded by a strong nebulosity, and that in the photograph referred to this spot appears as one of the principal foci of the great spiral nebula. These considerations naturally lead to the conclusion (which has also been reached upon other grounds so far as the larger stars are concerned) that Epsilon and the other leading stars of Orion, with the exception of Betelgeuse, which lies beyond the boundaries of the nebula, are at practically the same distance from us as the small stars surrounding them, all being members of one system.

There are many such star-streams to be found in the sky where as yet no related nebulæ have been discovered. But one can hardly doubt, in view of the evidence which the photographs we have referred to furnish, that the forms of the streams are derived from the pre-existing forms of the parent nebulæ. In many cases, of course, the process of nebular condensation has been finished, and we can never expect to discover any evidence of the nebula having once existed beyond the peculiar configuration of the stars to which it gave birth. In other cases, as in this of Orion, photography may yet reveal to us the existence of faint nebulous spirals still connected with the star-groups. Prof. Holden's discovery of a starry ring connected with the celebrated ring nebula in Lyra is in direct accord with the revelations of photography in this respect. Another interesting example is furnished by Mr. W. F. Denning's discovery last September of a small nebula which is completely encircled by a ring of stars. It is impossible, when looking at Mr. Denning's sketch of this curious object in The Observatory, to think that the stars and the nebula there shown do not belong to a single system.

Among the most striking examples of curved or spiral stellar arrangement are the circlet of small stars surrounding Delta