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KNOWLEDGE & SCIENTIFIC NEWS. 



fSEfTEMBER, IQOS. 



wise direction emerges on opposite sides near the minor 

 axis. "••■ Even the apparent ring form of this nebula 

 seems to be fictitious. Instead of being annular in 

 shape, it appears to be a hollow spheroid, the ring re- 

 presenting the thickness of the shell. To anyone who 

 still. persists in miiintaining the theory of ring forma- 

 tion in nebuljB it may be said that the whole heavens 

 are against him. 



It has always been difficult to imagine how rings 

 could possibly be formed from the parent mass, con- 

 sidering the extreme tenuity of the original nebula. 

 Computing from the total mass of the bodies composing 

 the solar system, the density of the primitive nebulous 

 mass — supposing it extended to the orbit of Neptune — 

 would have been almost inconceivably small. The 

 density of atmospheric air would be millions of times 

 greater, and how rings could be formed in such a 

 tenuous gas has always been a serious dilhculty in the 

 -discussion of Laplace's Hypothesis. But a still more 

 fatal objection has lately been found. The original 

 idea was that the detached " rings " would at first 

 break up into separate masses, and that these frag- 

 ments would afterwards — by their mutual attraction — 

 consolidate into planets. But from a mathematical in- 

 vestigation recently undertaken by the well-known 

 American mathematician, Mr. John N. Stockwell, he 

 finds that if two masses " are moving in the same 

 plane and at the same mean distance from the sun, and 

 are situated at an angular distance greater than 60° 

 and less than 180° from each other, as viewed from the 

 sun, their mutual perturbations will cause them to ap- 

 proach each other until the distance apart becomes 

 equal to 60° " ; and, further, if the two masses "are 

 situated at an angular distance of less than 60° apart, 

 as seen from the sun, their mutual perturbations will 

 cause them to recede from each other until their 

 distance apart becomes equal to 60°; and they will 

 always remain in a condition of stable equilibrium at 

 that distance apart, and w'ill revolve round the sun 

 for ever free from mutual disturbance. "t 



This result seems fatal to Laplace's Hypothesis in its 

 original form, as the fragments of the ruptured ring 

 could never have consolidated into a single planet. 

 Mr. Stockwell adds : " The assumption by Laplace that 

 the matter of which the ring was composed would con- 

 centrate by the mutual attraction of its different parts 

 into a single planet or satellite is, therefore, not sus- 

 tained by a rigorous calculation; and since the Nebular 

 Hypothesis wholly fails to satisfy that requirement it 

 evidently rests on no logical foundation." 



Compelled, therefore, as we apparently are, to aban- 

 don Laplace's Nebular Hypothesis in its original form, 

 are we, therefore, obliged to relinquish all attempts to 

 explain the formation of suns and solar systems from 

 the consolidation of gaseous matter? By no means. 

 The heavens, which are clearly against Laplace's 

 Hypothesis, are strongly in favour of a new theory, a 

 new- cosmogony, which will probably stand the test of 

 mathematical analysis. This is the evolution of suns 

 and svstems from spiral nebulte. Of the half-million 

 nebulae discovered with the Crossley reflector a large 

 proportion are spiral, and the study of these remarkable 

 and interesting objects will probably form an important 

 portion of the work of future astronomers. 



I Nature, August 6, 1903. 



\ Astrophysical Journal, No. 557, March 4. 1904. An asteroid 

 recently dicovered (TG) has nearly the same period and mean 

 distance as Jupiter, and seems to fulfil the conditions supposed by 

 Stockwell. At present it is Co- from Jupiter, and may _perh aps 

 remain so. 



Laplace's original nebula was gaseous, and a gaseous 

 spectrum shows bright lines. But the spectrum of the 

 spiral nebula; is continuous, indicating that they have 

 partially consolidated from the gaseous state. We can, 

 therefore, easily imagine that masses might be thrown 

 oft or detached from the parent mass by the centrifugal 

 force of the rotation. This seems much more probable 

 than the formation of rings from a highly tenuous 

 nebula. Photographs of spiral nebulae show us masses 

 in the act of being detached from the spiral branches. 

 This is particularly noticeable in the photograph of the 

 great spiral in Canes Venatici (51 Messier), in which 

 we see the process going on before our eyes. 



The theory of the evolution of suns and solar systems 

 from spiral nebulaj has recently been investigated 

 mathematically by Professor T. C. Chamberlin and 

 Mr. F,- R. Moulton. ^ This investigation consists in an 

 attempt " to test by an appeal to the laws of dynamics 

 the consistency of the ring theory with known pheno- 

 mena. Contradictions were uniformly found, and in 

 some cases the results were so conclusive as to compet 

 us frankly to abandon it as an untenable hypothesis."* 

 An outline of this new cosmogony, called by Professor 

 Chatnberlin the " Planetesimai Hypothesis," and which 

 certainly seems a great improvement on that of Laplace, 

 may prove of interest to the general reader. 



The origin of the nebulous mass from which the solar 

 system is supposed to have been evolved was not con- 

 sidered by Laplace. He assumed its existence, and then 

 proceeded to show, as he thought, how the sun and 

 planets might have been formed from it by the con- 

 solidation of the nebulous matter in the course of ages. 

 The origin of spiral nebulae is, of course, unknown, but 

 of their existence there can be no doubt. Photography 

 has fully confirmed the discovery originally made by 

 Lord Rosse with his giant 6 feet telescope. They are 

 very numerous in the heavens. Professor Keeler 

 thought that probably one-half of the nebulae found with 

 the Crossley reflector are spiral, and that " any small 

 compact nebula not showing evidence of spiral structure 

 appears exceptional." Spiral nebulae w-ere, of course, 

 unknown to Laplace, and had he known of their exist- 

 ence we should probably never have heard of " ring 

 formation. " 



A spiral nebula may possibly have been formed by a 

 " grazing collision " of two solid or nebulous masses, 

 or by the near approach of two bright stars. Sup- 

 posing the near approach of alarge body to another of 

 larger size, the effect on the latter body would be the 

 production of a gigantic tide on the side turned towards 

 the approaching body, and another tide of almost equal 

 size on the opposite side. These tides would produce 

 explosions and eruptions of nebulous matter from the 

 interior of the star, and Moulton shows that the ejected 

 material would assume the spiral form. That a spiral 

 form would be assumed by a rotating gaseous mass 

 has also been shown by Herr E. J. Wilczynski, of 

 Berlin.! Xow it is a remarkable feature of spiral 

 nebulae that the spiral branches (usually two) almost 

 invariably issue from the central nucleus at diametri- 

 cally opposite points, thus agreeing with the new 

 hypothesis. The spiral nebulae which we see in the 

 heavens are, of course, constructed on a colossal scale, 

 and probably represent a stage in the evolution of star 

 systems rather than solar systems like ours. But the 

 principle would be the same in both cases. 



In Chamberlin's " Planetesimal Hypothesis " the 

 original nebulous mass "must have spread out in the 



"Astrophysical Journal, October, 1905. 



t Astrophysical Journal, Vol. 4 (i8g6), p. 98. 



