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The photographic news
- Bandzählung
- 35.1891
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- 1891
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- Hochschule für Grafik und Buchkunst Leipzig
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- Bandzählung
- No. 1724, September 18, 1891
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The photographic news
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654 THE PHOTOGRAPHIC NEWS. [September 18, 1891. means that the larger stars give a million times as much light as the smaller stars, and in the photograph of the Coal- Sack region of the Milky Way there is evidence of a still greater range of magnitudes. The star a Crucis, which is of the 1’3 magnitude, is evidently associated with a den se cluster of small stars, branches from which can be traced far across the Coal-Sack region, and extending to a considerable distance over the Milky Way, or into the Milky Way, to the north of a Crucis. We seem to have in this instance evidence of a range of at least 17 magnitudes; and the proof of the connection between the large star and the small stars of the cluster is far stronger than as stated by me in the May number, a Crucis is a double star with components about five seconds apart, and there are several small companions that have been observed in the telescope. In the glass photographs sent me by Mr. Russell, the spurious disc of the large star is, when examined with a magnifier, seen to contain several small stars forming a cluster about the large one. Indeed, in the plate pub lished in the May number, some seven or eight of these small stars may be recognised with a magnifying-glass on the edge of the spurious disc of the large star. Though the mind may at first be staggered by the con ception of stars giving a million times as much light as our sun, we are not in a position to deny the existence of such vast sun-like bodies. Indeed, those who accept the nebula hypothesis as giving the most probable explanation of the origin, or, rather, of the birth of the planets of the solar system, must be prepared to believe that there was a time when the sun had a diameter as large, or nearly as large, as the diameter of the orbit of Neptune. If, before these more than geologic ages of radiation into space, the surface or photosphere of the solar mass did not shine as brightly as it shines now, it must at least have been a nebula with a very definite surface, which, as seen from a distance of a hundred times as great as that of a Centauri, would have presented a disc nearly half a second in dia meter. No. disc has at present been observed to any star ; we may therefore feel some confidence that there is no such vast sun-like body within a distance from us equal to fifty times the distance of a Centauri. In the forthcoming part of the “Old and New Astro nomy ” I have shown reason to believe that there is evi dence of absorption of light in space, and that we can, from the numbers of the stars of the various magnitudes, make a rough minimum estimate as to the amount of absorption of light in space, due either to a want of perfect elasticity in the light-transmitting ether, or to dark bodies cutting out or obliterating the light in its passage through space. This greatly reduces our idea of the magnitude of the region we can explore with the telescope and with the camera—a Centauri would probably be lost to the Lick telescope if it were removed to three hundred times its present distance—and it also greatly reduces our idea of the distance of the small stars of the Milky Way, and of the scale of the galactic system, as well as of the nebular system and of the system of clusters, red stars, and bright line stars which are so evidently associated with it. It is not so very long ago that it was generally taught that the nebulae were galaxies of stars more or less similar to the Milky Way that surrounds us, but so inconceivably remote as to appear, when observed with the largest tele scopes, like small spots in the heavens. This theory suited the popular taste, and died hard. It involved the assump tion that man could explore, with the instruments at his disposal, a space so immense that the interstellar spaces which we can just measure or guess at are dwarfed into points besides the distance from which light travels to us. The theory should have been disposed of by the observa tions of Sir William Herschel, who noted that many nebulae are evidently associated with stars, and observed that the smaller nebulae were distributed over the heavens in a manner which shows an intimate connection between them and the brighter stars. He noted that the nebulae in the northern heavens were clustered in the pole of the Milky Way, and descended like a canopy on all sides, leaving a dark space or channel separating the nebulous region from the rich stellar region of the Milky Way. Sir William Herschel also fully satisfied himself that “ there were nebulosities which are not of a starry nature,” and from his observations of diffused nebulae he formed his well-known hypothesis of a diffused luminous fluid which, by its eventual aggregation, produced stars. But he did not proceed to the legitimate deduction from hisobserva- tions as to the general distribution of nebula;—viz., that nebul which are arranged so symmetrically with respect to the stars must belong to the stellar system, and there fore cannot be assumed to lie at immense distances com pared with the distance of the Milky Way stars. Sir John Herschel extended the observations of his father to the southern heavens, and showed that there was a similar clustering of the smaller nebul on the southern side of the Milky Way, and a similar intimate connection between the distribution of stars and the distribution of nebulae in the southern hemisphere (see “ Cape Observa tions,” p. 134) ; but it was not till 1858 that the obvious conclusion from these observations was drawn by Mr. Herbert Spencer in a remarkable paper on “ The Nebular Hypothesis,” published in the Westminster Review. He remarked: “ If there were but one nebula, it, would be a curious coincidence were this one nebula so placed in the distant regions of space as to agree in direction with a starless spot in our own sidereal system. If there were but two nebul, and both were so placed, the coincidence would be excessively strange; what, then, shall we say on finding that there are thousands of nebul so placed ? Shall we believe that in thousands of cases these far- removed galaxies happen to agree in their visible positions with the thin places in our own galaxy ? Such a belief is impossible.” Mr. Herbert Spencer’s paper was not illustrated by charts, and the force of his reasoning was not generally perceived till some ten years afterwards, when Prof. Cleveland Abbe drew attention, in the Monthly Notices of the Royal Astronomical Society for May, 1867, to the intimate connection between the distribution of nebula; in space and stars; and Mr. Proctor, in 1869, constructed some charts on an equi-surface projection, which graphic ally put his readers in possession of the facts, and carried conviction to all who read his remarks. The theory that the nebul were distint galaxies in volved the assumption that light can reach us from regions many thousand times more remote than the stream of stars which compose our own galaxy ; and it also involved the assumption that the matter of the universe is aggregated into clusters, separated by immense barren spaces, in which we must assume that there are very few luminous stars, and but few dark stars which would absorb light, as well as comparatively very little opaque matter dis tributed as meteors are distributed in the region of space we are familiar with. We have evidence that the greater part of the lucid
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