Geology. 195 



other in the equatorial zone. The problem, to be solved is whether 

 bodily separation of a portion of the spheroid would tend to take 

 place, or whether it would shed material molecule by molecule. 

 A discussion of the several outer zones of gas is given following 

 the lines pursued by G. Johnston Stoney, and it is shown that 

 molecules in the outer zone which reach the critical parabolic 

 velocity will be directed forward owing to the velocity of rota- 

 tion being added to the velocity of impact from behind. A cer- 

 tain per cent will further be given larger orbits owing to impact 

 from below, and will thus become minute and independent satel- 

 lites. In conclusion, Chamberlin states : 



" Those molecules which make elliptical flights and return to 

 the spheroid without collision carry back whatever moment of 

 momentum they took out, but those thrown into permanent orbits 

 retain, as a rule, not only what they took out but also the addi- 

 tional moment of momentum gained from the collisions which 

 gave these free orbits. It follows that every molecule that goes 

 into a free orbit takes a disproportionate amount of the moment 

 of momentum of the spheroid and thus reduces its rotation, or 

 else retards its increase of rotation, to that extent" * ' * * 



" From the nature of the case, I entertain, with others, the 

 view that the separation must take place molecule by molecule, 

 and it seems to me inevitable that these molecules must go into 

 orbits each carrying an excess of momentum at the expense of 

 the spheroid, and hence that the critical stage of exact balance 

 between the centrifugal and centripetal factors of the spheroid 

 is never reached. If so, bodily separation is excluded by the 

 conditions of the case. 



"The conviction that such rotating gaseous spheroids must shed 

 portions of their matter molecule by molecule, if they do so at 

 all, has long been held by students of the subject, but I am not 

 aware that the loss of moment of momentum from the spheroid 

 has been urged as a reason why the critical state prerequisite to 

 bodily separation may not be attainable " (p. 167). 



The result of these last two papers goes to show on independ- 

 ent lines that celestial bodies cannot suffer bodily disruption 

 owing to cooling and shrinking of their own mass attended by 

 acceleration of rotation. 



The following paper is on " Geophysical Theory under the 

 Plcmetesimal Hypothesis" by Arthur C. Lunn : 



"This paper is devoted mainly to a quantitative study of that 

 portion of the earth's internal energy which is supposed to have 

 been derived from the mechanical energy of a primitive system 

 of planetesimals, of its transformation into thermal form during 

 the epoch of accretion, and its subsequent redistribution by con- 

 duction " (p. 171). 



It occupies sixty pages, and brings out important mathemati- 

 cal relations, but as it involves details regarding centrospheric 

 conditions consequent upon one hypothesis of earth origin and is 

 not so evidently a test of hypothesis, a detailed discussion may be 

 omitted from the present review. 



