Feb. 24, 1 881] 



NA rURE 



389 



" The instruments would be returned, in perfect order, as 

 soon as possible after the transit, and, in any case, before 

 the end of 18S3. 



" All communications should be addressed to the 

 Secretary, Transit Committee, Royal Society, Birling- 

 ton House." 



The Committee, we are informed, is constituted as 

 follows ; — The President of the Royal Society is the 

 chairman, the other members being Prof. J. C. Adams, 

 the Astronomer-Royal, the Eari of Crawford and Bal- 

 carres, Mr. De la Rue, :\Ir. Hind, Dr. Huggins, Vice- 

 Admiral Sir G. H. Richards, Prof. H. J. S. Smith, Prof 

 Stokes, and Mr. E. J. Stone. 



DR. J. J. BIGS BY 

 'V/'ET another of the links that have bound the geologists 

 ^ of the present time in association with the early 

 leaders of their science has been severed by the removal 

 of the kindly and venerable form of Dr. Bigsby. Up- 

 wards of sixty years ago he began his geological career in 

 North America, devoting himself mainly to the investi- 

 gation of the structure of the older Palaeozoic rocks of 

 Canada and of the adjoining tracts of the States. As 

 secretary to the Boundary Commission under the Treaty 

 of Ghent he had opportunities of investigating the region 

 from Quebec to Lake Superior, and published numerous 

 descriptions, of which the exactness has been amply 

 verified by the subsequent researches of the Geological 

 Survey of Canada. It is chiefly as an admirable pioneer 

 in Canadian geology that his name will be inscribed in 

 the records of scientific progress. But he has other 

 claims to grateful remembrance. Since he returned to 

 spend his later years in this country he has devoted 

 himself with the most untiring patience to the compi- 

 lation of his "Thesaurus Siluricus" and "Thesaurus 

 DeYonicus" — works in which the geological and geo- 

 graphical range of the organisms of the earlier half of 

 Palaeozoic time is clearly shown in a series of valuable 

 tables. 



Still more recently, in 1S77, he presented to the Geologi- 

 cal Society a bronze medal which, with a sum of money de- 

 rived from the interest of a fund also given by him, is to be 

 awarded every two years as an incentive to geological study. 

 The terms according to which he directed that the prize 

 should be given are that the medal and interest from the 

 fund should be a.varded " as an acknowledgment of emi- 

 nent services in any department of geology, irrespective 

 of the receiver's country ; but he must not be older than 

 forty-five years at his last birthday, thus probably not too 

 old for further work, and not too young to have done 

 much." The founder lived to see two fitting awards of 

 his prize go to the eminent paleontologists of the United 

 States, Professors O. C. Marsh and E. D. Cope. He died 

 just before the third presentation was made, last week, to 

 Dr. Charles Barrois of Lille. 



ON TIDAL FRICTION IN CONNECTION WITH 



THE HIS TOR Y OF THE SOLAR SYSTEM'^ 

 'T^HIS paper forms one of a series on the subject of 

 -•■ tidal friction which have been read from time to time 

 before the Royal Society and reported in Nature. 



The first part of the paper contains the investigation of 

 the changes produced by tidal friction in the system 

 formed by a planet with any number of satellites revolving 

 about it in circular orbits. As the results cannot be con- 

 veniently stated without the aid of mathematical notation, 

 they are here passed over. 



The previous papers treated of the effects which tidal 



; of a piper entitled " On the Tid.il Frictioa of a Planet 

 attended by several Satellites, and on the Evolution of t!ie Solar System." 

 by G. H, Darwin, F.R.S., read before the Royal Society on januar)- 20, 



friction must have had on the motions of the earth and 

 moon, on the supposition that time enough has elapsed 

 for this cause to have its full effect. It then appeared 

 that we are thus able to co-ordinate together the various 

 elements of the motions of these t«o bodies in a manner 

 too remarkable to bo the product of chance. 



The second part of the present paper contains a dis- 

 cussion of the part which the same agency may have 

 played in the evolution of the solar system as a whole and 

 of its several parts. 



It is first proved that the rate of expansion of the 

 planetary orbits, due to the reaction of the frictional tides 

 raised by the planets in the sun must be very slow 

 compared with that due to the reaction of the tides 

 raised by the sun in the planets. Thus it would be much 

 more nearl)' correct to treat the sun as a rigid body, and 

 to suppose the planets alone to be subject to frictional 

 tides, than the converse. It did not, however, seem 

 expedient to attempt to gii^e [any numerical solution of 

 the problem thus suggested which should apply to the 

 solar system as a whole. 



The effect of tidal friction is to convert the rotational 

 momentum of the tidally disturbed body into orbital 

 momentum of the tide-raising body. Hence a numerical 

 evaluation of the angular momentum of the various parts 

 of the solar system will afford the means of forming some 

 idea of the amount of change in the orbits of the several 

 planets and satellites, which may have been produced by 

 tidal friction. Such an evaluation is accordingly made 

 in this piper, with as much accuracy as the data permit. 



From the numerical values so found it is concluded 

 that the orbits of the planets round the sun can hardly 

 have undergone a sensible enlargement from the effects 

 of tidal friction since those bodies first attained a separate 

 existence. 



Turning to the several sub-systems, it appears that, 

 although it is possible that the orbits of the satellites of 

 Mars, Jupiter, and Saturn about their planets may have 

 been considerably enlarged, yet it is certainly not possible 

 to trace the satellites back to an origin almost in contact 

 with the present surfaces of their planets, in the same 

 manner as was done for the case of the moon in the 

 previous papers. 



The nuiuerical values above referred to exhibit so 

 marked a contrast between the ca^e of the earth with 

 the moon, and that of the other planets with their satel- 

 lites, that it might a priori be concluded as probable that 

 the modes of evolution have differed considerably. The 

 conclusion above stated concerning the satellites of the 

 other planets cannot therefore be regarded as unfavour- 

 able to the acceptance of the views maintained in the 

 previous papers. It must, however, be supposed that 

 some important cause of change other than tidal friction 

 has been concerned in the evolution of the solar system 

 and the planetary sub-systems. According to the nubu- 

 lar hypothesis of Lapla;e, that cause has been the con- 

 densation of the heavenly bodies. Accepting that hypo- 

 thesis, the author then proceeds to consider the manner 

 in which contraction and tidal friction are likely to have 

 worked together. 



A numerical comparison shows that, notwithstanding 

 the greater age which the nebular theory assigns to the 

 exterior planets, yet the eflects of solar tidal friction in 

 reducing planetary rotation must in all probability be 

 considerably less for the remote than for the nearer 

 planets. It is, however, remarkable that the number 

 expressive of the rate of retardation of the Martian rota- 

 tion by solar tidal friction is nearly the same as the 

 similar number for the earth, notwithstanding the greater 

 distance of Mars from the sun. This result is worthy of 

 notice in connection with the fact that the inner satellite 

 of Mars revolves with a periodic time much shorter than 

 that of the planet's rotation; for (as suggested in a 

 previous paper) solar tidal friction will have been com- 



