April 2, 1885] 



NA TURE 



50/ 



reader to refer to the essay in the " Annuaire " of the 

 Bureau des Longitudes, 1SS5, for this portion of his 

 work. M. Kayc's writing is always easy and finished, 

 and this essay has been intended for the general scientific 

 reader. Had the original speculation been condensed for 

 insertion in a purely technical journal it would have 

 occupied but a few pages. 



The earlier portion of the essay we may dismiss by 

 saying that it gives a lucid exposition of the state of our 

 knowledge of stellar systems, as derived from the spectro- 

 scope and the telescope, interpreted by aid of the prin- 

 ciple of conservation of energy. In the following descrip- 

 tion of M. Faye's theory, we do not follow his words, but 

 we believe that we give a fair interpretation of his 

 meaning. 



The best general idea of the line of speculation adopted 

 may be given by saying that it is a theory of evolution 

 from meteorites, instead of from the nebulous matter 

 which gives its name to Laplace's theory. 



In its primitive condition the Universe consisted of 

 matter widely scattered in chaotic disorder. Currents 

 were then generated in the midst of this chaos under the 

 influence of mutual gravitation ; and in consequence of 

 these intestinal movements rags or shreds of matter 

 became detached, and moved with rapid linear and slow- 

 gyratory mot;< n. 



It is not claimed that the existence of these currents 

 can be explained, but the spectroscope affords evidence 

 of a sorting process, for some nebula; consist of a single 

 gaseous element, whilst the stars with continuous spectra 

 consist of a great diversity of elements. 



The various modes are sketched in which one of these 

 shreds may proceed to agglomerate and evolve itself, but 

 we shall not follow M. Faye in the application of his 

 theory to the formation of nebulae, double-stars, and star- 

 clusters. 



The solar system is taken to have originated from a 

 shred which aggregated into a spheroidal shape, and 

 consisted, at the epoch when we begin to watch it, largely 

 or principally of separate meteorites. The spheroidal 

 aggregate possessed a considerable amount of rotation 

 (moment of momentum), about an axis approximately 

 identical with the axis of the sun's rotation. 



It is at first supposed that the spheroidal aggregate 



of matter pretty nearly equally distributed 



out its volume, and later a nucleus is formed. 



If r be the distance of any point from the centre, the 



force is central, and follows the law a r -\- -, where, in the 



>- 

 beginning of the evolutionary process, b is very small, and 

 later a becomes small. 



Initially, then, when the force is simply as the distance 

 from the centre, each meteorite moves in an ellipse about 

 the centre, and the periodic time of all of them is the 

 same, whatever their eccentricity of orbit. Those meteor- 

 ites whose orbits are decidedly eccentric, cross the orbits 

 of many others, and have much less chance of escaping 

 collision than those whose orbits are nearly circular. In 

 consequence of collisions, a central nucleus is soon 

 formed, and then many meteorites with very eccentric 

 orbits begin to strike against it, and to be absorbed into 

 it. As the nucleus increases the a in our formula for the 

 force diminishes, and the b increases ; but orbits which 

 are circular still retain that form, notwithstanding the 

 progressive change in the law of force. 



At the same time that the nucleus is being formed, a 

 series of flat and nearly circular rings arise around it, 

 those near to the nucleus attaining a definite shape sooner 

 than the remote ones. It is not adequately explained 

 why the matter should be sifted, and should arrange itself 

 in rings at definite intervals around the nucleus ; still less 

 is any light thrown on the law of Titius concerning the 

 distances of the planets from the sun. Nor do we see 

 why the rings should first be formed nearest to the 



nucleus. We must, however, here follow M. Faye and 

 accept these conclusions. 



If there be only a small nucleus (b small), each ring 

 revolves with very small relative motion of its parts : 

 whilst if the nucleus be large {a small), each meteorite in 

 a ring revolves after Kepler's laws, and the bodies in the 

 external margin have a slower angular velocity than those 

 in the internal margin. As the nucleus gradually in- 

 creases there will be a transition from one mode of motion 

 to the other. 



Now let us follow the first ring : — Slight differences of 

 angular velocity, mutual attractions between the parts of 

 the nng and collisions gradually cause the aggregation 

 of all the matter in the ring around some centre in its line. 

 When the nucleus is small the ring moved as a rigid 

 whole, and the linear velocity of the outer meteorites was 

 greater than that of the inner ones, therefore when the 

 planetary aggregate is formed it will be found rotating 

 with direct motion about an axis nearly perpendicular to 

 the plane of its orbit. 



Whilst the first ring is agglomerating into a planet, a 

 second ring is being formed outside of it, and this in its 

 turn agglomerates ; but the tendency to direct rotation 

 is weaker than in the lirst planet, because the increase of 

 the solar nucleus by absorption of meteorites has pre- 

 vented so large an excess of linear velocity of the outer 

 meteorites over that of the inner ones as in the first case. 



The process continues and the planets are sue 

 formed, until we come to an epoch when the nucleus has 

 increased so far that on agglomeration the tendency to 

 direct rotation vanishes — the constituent ring, in fact, 

 revolved irrotationally. 



Still further we come to planets in which the meteorites 

 move nearly according to Kepler's laws, and here the 

 resulting planet has a markedly retrograde rotation. 

 Each planetary agglomeration in its turn forms a minia- 

 ture solar system, and generates satellites by the same 

 process as that in which the planets were formed. 



We have now sketched this theory in its main outlines, 

 and must refer the reader to the original sources for 

 further details. 



Neither in the historic part nor in his cosmogonic 

 speculations does M. Faye make reference to the possible 

 effects of tides in the evolution of the solar system, 

 perhaps thinking that a theory founded on that influence 

 is not even worthy of mention. It is, however, a factor 

 which cannot be left on: of account. Tidal friction is a 

 veraccatsa, and the possible effects on our evolution have 

 been submitted to a rigorous quantitative examination. 1 

 As it is the only cosmogonic influence which has hither- 

 to been so treated, the results to which it points are at 

 least as worthy of attention as those of other vaguer 

 influences. 



The hypotheses that tidal friction has had free play in 

 the past leads to a remarkable quantitative coordination 

 of the several elements of the earth's rotation, and of the 

 moon's orbital motion, and points to the genesis of the 

 moon close to the present surface of the earth. No phe- 

 nomenon in the heavens could have been devised more 

 perfectly apt to confirm the truth of the hypothesis than 

 the rapid orbital motion of the inner satellite of Mars. 

 Near to the sun solar tidal friction would be much more 

 powerful than at a distance, and thus the rotation neces- 

 sary for the manufacture of satellites would be destroyed 

 in the vicinity of the sun ; a light is thus thrown on the 

 cause of the observed distribution of satellites in the 

 system. - 



It has, however, been decisively shown that tidal fric- 

 tion cannot have played the leading part either in the 

 evolution of the whole solar system or of the remoter 



1 \v, ref< ; ers by the present writer on thi<? subject in the 



Phil. '/',.: in 1878 to 1882. 



tidal friction h.is not been c mmented on by 

 .-myurit.T Further numerical details and discussicn will be found in Phi . 



