523- 



KDooiledge & Seientlfie Nems 



A MONTHLY JOURNAL OF SCIENCE. 



Conducted by MAJOR B. BADEN-POWELL, F.R.A.S., and E. S. GREW, M.A. 



Vol. III. No. 22. 



[new series.] SEPTEMBER, 1906. 



SIXPENCE NET. 



CONTENTS—See page V. 



The Ne^v Cosmogony. 



By J. E. Gore, F.R.A.S. 



In Laplace's Nebular Hypothesis, the original mass, 

 from which the solar system was evolved, was supposed 

 to consist of gaseous or meteoroidal material filling a 

 space of spheroidal form and extending to the orbit of 

 the planet Neptune, or somewhat beyond it. If a 

 gaseous state be assumed the whole mass was supposed 

 to be in hydrodynamical equilibrium, and rotating in a 

 period equal to the period of revolution of the present 

 farthest planet. We might also assume that the 

 original mass consisted of a gigantic swarm of 

 meteorites, for Professor G. H. Darwin has shown that 

 such a swarm would have nearly the properties of a 

 gas. On either assumption the mass would contract 

 by its own gravitation, and, the angular velocity gradu- 

 ally increasing, the centrifugal force would in time 

 flatten the spheroidal mass at the poles. From this 

 flattened spheroid Laplace thought that rings would be 

 detached at certain intervals, and these rings consoli- 

 dating would eventually form the planets and satellites 

 of the solar system as we now see them. 



It has been shown, however, by Mr. F. R. Moulton, 

 that the matter detached from the rotating gaseous 

 spheroid would be " shed continually," and that no 

 separate rings could be formed. This would c)ccur 

 whether we consider the original mass to have been 

 gaseous or composed of meteorites. But supposing 

 the rings to have been, by some miracle, detached from 

 the parent mass, we should expect to find that the plane 

 of Mercury's orbit would deviate less than the other 

 planets from the average plane of the solar system; 

 also that the orbits of the " terrestrial planets," 

 Mercury, Venus, the Earth, and Mars, would be less 

 eccentric, that is, more nearly circular, than those of 

 the outer planets. But the known facts concerning 

 Mercury's orbit are quite opposed to these conclusions. 

 The inclination of its orbit to the plane of the ecliptic 

 (7°) 's greater than any of the large planets, and the 

 eccentricity of its orbit (0.20) is only exceeded bv that 

 of some of the minor planets between Mars and Jupiter. 

 Further, Moulton shows that the distribution of masses 

 among the planets of the solar system indicates that the 

 original nebulous mass must have been very hetero- 

 geneous and not homogeneous as Laplace's theory 

 postulates.* 



• Aitrophysical Journal, March, 1900. 



There are numerous other difficulties connected with 

 Laplace's Hypothesis, and many attempts have been 

 made to overcome them. But these efforts have proved 

 only partially successful, and for some years past it has 

 become increasingly evident that the hypothesis must 

 be abandoned for something- in better agreement with 

 modern telescopic discoveries. The idea that the 

 planets were formed by the condensation of rings de- 

 tached from a nebulous mass is an hypothesis for which 

 we find no warrant in the heavens. Laplace's idea of a 

 Nebular Hypothesis was probably suggested by a con- 

 sideration of Saturn's rings. But modern researches 

 on tidal action tend to show that this wonderful system 

 was not originally formed as a ring left behind by 

 Saturn during the progress of condensation from the 

 nebulous stage. More probably the matter composing 

 the rings was originally separated from the planet in 

 one mass. This mass being too close to Saturn to con- 

 solidate into a satellite — being within what is known 

 as " Roche's limit " — was torn into fragments by the 

 force of tidal action, and its particles were scattered 

 round the planet in the form of a ring as we now see it. 

 On this view of the matter the course of events was 

 exactly the reverse of what was supposed to have 

 happened in Laplace's Hypothesis. Instead of a ring 

 being first formed, and then a number of small satellites 

 from this ring, we must now conclude that a mass of 

 matter was first detached from the partially con- 

 solidated planet, and that then this mass was broken 

 up into small fragments by the enormous tidal action 

 of the central mass. 



We see in the heavens numerous forms of nebulae — 

 spiral nebula-, planetary nebula, etc. — but there is no 

 real example of a ring nebula. Those which have been 

 termed "annular nebulfe " are most probably spiral 

 nebulte seen foreshortened. Of the numerous nebula? 

 recently discovered with the Crossley reflector at the 

 Lick Observatory it has been found that " a large pro- 

 portion are spiral, and that practically all the spirals 

 are lenticular or disc-shaped. Many of them are rela- 

 tively very thin."* At one time the photographs of 

 the great nebula in -Andromeda were thought to show 

 signs of ring formation, but Dr. Roberts, describing 

 his photograph of this wonderful nebula, says: "That 

 this nebula is a left-handed spiral and not annular, as I 

 at first suspected, cannot now be questioned; for the 

 convolutions can he traced up to the nucleus, which 

 resembles a small bright star at the centre of the dense 

 surrounding nebulosity." Even the "ring nebula" 

 in Lyra, which is sometimes adduced as an example of 

 ring formation, was found by Professor Schaeberle, of 

 the Lick Observatory, to be "a two-branched spiral 

 which commences at the central star, and in a clock- 



• Publications of the .Vstronomical Society of the Pacific, Dec. 

 10, 1904. 



