590 



NATURE 



[July 7, 1921 



into fragments which are our present system of 

 planets. From the mathematical investigation on 

 which this hypothesis is based, it appears that the 

 fragments would each be comparable in mass with 

 the original sun if the matter of the sun had been 

 of approximately uniform density, but would be 

 very small by comparison if the sun had been 

 gaseous with high central condensation. The 

 smallness of the masses of the planets in compari- 

 son with that of the sun must, therefore, be taken 

 as indicating that the sun was in a gaseous state 

 with high central condensation when the planets 

 were born. The jets of matter thrown out would 

 also be gaseous, but would rapidly cool in the pro- 

 cess of ejection, and might soon liquefy or even 

 solidify. It can be shown that the planets which 

 would be formed out of the middle portion of such 

 a jet ought to be much more massive than those 

 formed near the ends, and this may possibly pro- 

 vide an explanation of the comparatively great 

 masses of Jupiter and Saturn. We imagine that 

 the planets at first described orbits under the 

 combined gravitational action of the sun and the 

 passing star by which the cataclysm was caused, 

 but as this star receded they were left revolving, as 

 at present, around the sun. During their earlier 

 motion they may themselves have been broken 

 up by the tidal action of one or both of the big 

 masses present, and such a process may explain 

 the origin of the satellites of the planets 



Such, in its main outlines, is the tidal theory of 

 the genesis of the solar system. So far as can be 

 seen, a vast amount of further mathematical re- 

 search is needed before it can be either definitely 

 accepted or finally condemned. For myself, I find 



it more acceptable than the rotational theory, or 

 any other hypothesis so far offered, of the origin 

 of the solar system. Time does not permit of 

 a discussion of its difficulties, but I may perhaps 

 conclude by stating what seem to me to be its 

 main advantages over the rotational theory, 



(i) It escapes the well-known criticism of the 

 rotational theory that the present angular momen- 

 tum of the solar system is too small to be com- 

 patible with a previous rotational break-up, and 

 I do not know of any similar quantitative criti- 

 cism which can be brought against the tidal 

 theory. 



(ii) The solar system is arranged with reference 

 to two planes — the invariable plane of the system, 

 which contains the orbits of the outer planets, and 

 a second plane inclined at about 6° to the former 

 plane, which contains the sun's equator and the 

 orbit of Mercury. A system which had broken up 

 by rotation alone ought to be arranged sym- 

 metrically about one plane — the original invariable 

 plane of the system. On the tidal theory the two 

 planes of the solar system are readily explained as 

 being the plane in which the tide-raising star 

 moved past the sun, and the original plane of the 

 sun's rotation. 



(iii) Theoretical investigations suggest that there 

 is only one possible end for a rotating system, 

 namely, a binary or multiple star of the type 

 familiar to astronomers, and it is quite certain our 

 system is not of this type. Similar investigations 

 on tidal action suggest that the final end of a 

 system broken up by a tidal cataclysm ought to 

 show many of the features of our present solar 

 system. 



The Edinburgh Meeting 

 By Prof. J. H. A 

 Local Arrangements. 



THE British Association meeting to be held 

 during the week September 7-14 is the fifth 

 meeting of the Association to be held in Edin- 

 burgh, the previous meetings having been in 

 1834, 1850, 1871, and 1892. The last of these, 

 under the presidency^ of a distinguished son of 

 Edinburgh — Sir Archibald Geikie — was a memor- 

 able and successful meeting, and the citizens of 

 Edinburgh are anxious to make the forthcoming 

 meeting no less notable and successful. 



As at the last Edinburgh meeting, the reception 

 room, the headquarters of the Association, and 

 the bureau of information will, by permission of 

 H.M. Office of Works, be the Parliament Hall, 

 in which the Scottish Parliament met until the 

 Treaty of Union in 1707. One of the courts 

 adjacent to the hall will be used for the meetings 

 of council and of other administrative committees, 

 and by permission of the Faculty of Advocates 

 rooms in the advocates' library, which is adjacent 

 to Parliament Hall, have been provided for the 

 use of the president and general officers, and the 

 advocates' writing-room has been placed at the 

 disposal of members. The attention of members 

 NO. 2697, VOL. 107] 



of the British Association. 



SH WORTH, F.R.S. 



is directed to the rule prohibiting smoking in any 

 part of the library and in Parliament Hall ; a 

 smoking-room is provided near the reception 

 room. The usual postal (including telegraphic) 

 facilities will be provided in the post office at the 

 entrance to the reception room. 



The sectional meetings will be held in the 

 lecture rooms of the University. Six of the 

 sections will meet in the Old College, two in the 

 adjacent departments of natural philosophy and 

 engineering, three sections and the conference of 

 delegates in the University New Buildings (the 

 medical school of the University), and the remain- 

 ing two in the department of agriculture and 

 forestry, which is within four minutes' walk of the 

 University New Buildings and of the Old College. 

 In connection with several of the sectional meet- 

 ings, laboratory accommodation will be available 

 for apparatus and specimens which members may 

 desire to exhibit to illustrate their communications 

 to the sections. 



Writing-rooms will be provided in the Uni- 

 versity and in the Unions. The University library 

 in the Old College is to be open so that members 

 may consult books and the principal literary and 



