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SCIENCE 



[N. S. Vol. XLIV. No. 1129 



self gravitative power along the line between 

 the centers and give the expansive forces op- 

 portunity to rise to explosive violence along 

 that line. This tidal force is actually greatest 

 at the centers and would lead to a very deep- 

 seated disruption. The gas bolts shot out 

 would, owing to viscous resistances, be pulsa- 

 tory, and separated nuclei would therefore be 

 expelled. These nuclei and the associated dis- 

 persed matter would, on the nearer side, be 

 dragged sideways after the passing star. On 

 the reverse side the symmetrical tidal protru- 

 sions would be left behind, the sun being 

 dragged more than they. The result would be 

 a spiral nebula, a form which would meet the 

 dynamic demands of the existing solar system. 

 In comment upon this chapter, it should be 

 noted, however, that the innumerable spiral 

 nebulae of the heavens, although good illustra- 

 tions of the initial form of the solar system, 

 do not appear to be stages in a similar evolu- 

 tion. They are of a much greater order of 

 magnitude, they avoid the region where the 

 stars are clustered, are at remote stellar dis- 

 tances, and by their very number show a 

 notable duration of their form. On the other 

 hand, the postulated originally spiral form of 

 the solar nebula would have been evanescent. 

 Within a century from the time of origin all 

 except the outer nuclei would have completed 

 many revolutions about the sun. But the 

 different periodic times of the nuclei would in 

 a few revolutions have caused to disappear the 

 initial spiral form. It would become wound 

 up and further blended together owing to the 

 high ellipticities of the constituent orbits. 



Having attained this initial state, Chapter 

 VTI. deals with the Evolution of the Solar 

 System into the Planetary System. The build- 

 ing up of the planets is believed to have fol- 

 lowed three stages: first, the direct condensa- 

 tion of the nuclear knots of the spirals into 

 liquid or solid cores; second, the less direct 

 collection of the outer, or orbital and satelli- 

 tesimal matter; third, the still slower gather- 

 ing up of the planetesimal material scattered 

 over the zone between adjacent planets. This 

 third factor in Chamberlin's view is regarded 

 as very important and he believes this diffused 



matter contributed much of the earth sub- 

 stance, very slowly and in a dust-like form. 

 This is one of the critical points in the details 

 of the theory, unessential to the larger frame- 

 work, but upon which turns much of the 

 development of the following argument. In 

 earth-growth the denser planetesimal dust, 

 Chamberlin argues, tended to be somewhat 

 segregated into the primitive ocean basins and 

 served to maintain in them, as the earth was 

 built outward, a greater density than in the 

 elevated zones between. It seems a debatable 

 question to the reviewer if such a large pro- 

 portion of the added material was necessarily 

 dust-like and capable of being distributed by 

 the primitive atmosphere and ocean. Upon 

 the mean size of the incorporated units vari- 

 ous subhypotheses of consequences may be 

 built up. In the absence of knowledge Cham- 

 berlin's view may be accepted as the most prob- 

 able, but the problem illustrates the fertile 

 branching which is possible upon the trunk of 

 the planetesimal hypothesis. 



Chapter VTTL, entitled The Juvenile Shap- 

 ing of the Earth, occupies sixty-eight pages, 

 more than twice the average length of the 

 chapters. The earth is conceived as beginning 

 to hold an ocean by the time it contained 30 or 

 40 per cent, of its present mass. Erom that 

 time atmosphere and hydrosphere transported, 

 sorted and deposited the planetesimal dust, 

 building up the lighter material into protu- 

 berant areas, which became the continental 

 platforms. Great importance is attached under 

 the shaping agencies to periodical changes in 

 the rate of rotation. Accompanying a stage 

 of internal condensation, a corresponding 

 speeding up of the rotation would occur and 

 a relative subsidence of the polar areas. Sur- 

 face compression in high latitudes, surface 

 tension in the torrid zone, would accompany 

 such an increased oblateness of form. The slow 

 accumulation of planetesimals between stages 

 of condensation would, on the other hand, it is 

 thought, produce a checking of rotational veloc- 

 ity and the converse effects in earth-form and 

 in earth-strains. With growth there was thus 

 a rhythmic oscillation in strain. At times 

 when the polar areas were in tension it is 



