November 5, 190!l] 



SCIENCE 



643 



rotations, whereas most of the rotations of the 

 solar system are direct. Among the more con- 

 venient references showing the general ac- 

 ceptance of this view are the following: D. 

 Kirkwood, Am. Jour. ScL, XXXVIIL, Nov., 

 1864, pp. 1-2; A. Hinricks, Am. Jour. Sci., 

 XXXVII., 1864, pp. 48-52; D. Trowbridge, 

 Am. Jour. Sci., XXXIX., 1865, pp. 25^3 ; A. 

 Gierke, " History of Astronomy during the 

 Nineteenth Century," 1893, p. 383; H. Faye, 

 " Sur rOrigine du Monde," 1896, pp. 138-140, 

 164^171, 270-281; C. A. Young, "General 

 Astronomy," 1899, pp. 568-572 ; Sir Eobt. Ball, 

 "The Earth's Beginning," 1902, pp. 324-347; 

 A. Gierke, " Modern Cosmogonies," 1905, pp. 

 26-42. It was therefore clear that if this 

 deduction were valid it was fatal to all hy- 

 potheses of the planetesimal type; indeed its 

 supposed validity was probably the reason why 

 such hypotheses had not been entertained. 

 This apparently fatal bar was removed by 

 Chamberlin, who pointed out that in the case 

 of bodies moving in elliptical orbits about a 

 common center, collision can only take place 

 when some part of the perihelion section of 

 the outer orbit coincides with some part of the 

 aphelion section of the inner orbit, and that 

 at the point of collision the body in the outer 

 orbit moves faster than the body in the inner 

 orbit, though on the average the body in the 

 larger orbit moves slower than the one in the 

 smaller orbit, which general fact was made the 

 basis of the previous adverse reasoning. The 

 way was thus opened for the construction of 

 a tenable hypothesis on the orbital basis, in- 

 cluding the form later called planetesimal. 

 This germ of constructive work on lines pre- 

 viously regarded as untenable was briefly 

 stated in the paper read before the British 

 Association for the Advancement of Science, 

 Toronto meeting, August 20, 1897, and pub- 

 lished in the Journal of Geology, October- 

 November, 1897, p. 669. 



Third Step. — The tenability of construction 

 on an alternative line being thus assured, the 

 skepticism regarding the old nebular and me- 

 teoroidal hypotheses was more freely enter- 

 tained and led to a search for other tests, 

 particularly those resting on grounds other 



than molecular activity. The discrepancj' be- 

 tween the slow rotation of the sun at present 

 and the rotation it should have if it had con- 

 tracted from a gaseous spheroid filling the 

 orbit of Mercury and having the equatorial 

 velocity necessary to shed the Mercurial ring 

 as postulated by the Laplacian hj-pothesis, 

 first came to Chamberlin's attention and led 

 to a conference, with Moulton, late in 1899, 

 out of which grew the more systematic in- 

 spection of the dynamics of the solar system 

 in which the chief work was done by Moulton. 



Fourth Step. — By restoring theoretically, in 

 conformity with the laws of gases, the nebu- 

 lous stages of the Laplacian hypothesis, com- 

 parisons of the several moments of momenta 

 of the spheroid at these stages with the mo- 

 ments of momenta of the equivalent parts of 

 the existing system were made by Moulton 

 with results that seemed fatal to the Laplacian 

 hypothesis and to all other hypotheses which 

 had a similar dynamic basis.' Several other 

 tests of a dJ^lamical character equally adverse 

 to the Laplacian hypothesis were also set 

 forth in this paper. 



Although the restorations of the solar spher- 

 oids at the various nebulous stages were made 

 on the basis of the known laws of distribution 

 of gases, with liberal margins of safety, imcer- 

 tainty as to the full trustworthiness of the 

 extension of the laws of gases to bodies of 

 such tenuity and at such temperatures was un- 

 avoidable. To cover doubts arising from this 

 source, independent tests were made by Cham- 

 berlin on the basis of the ratios of the masses 

 to the moments of momenta of the spheroids 

 and of the separated rings, respectively, using 

 the masses and the moments of momenta of 

 the present derived bodies, thus avoiding the 

 application of the laws of gases; and the re- 

 sults were found to be equally adverse to the 

 Laplacian hypothesis.' 



' " An Attempt to Test the Nebular Hypothesis 

 by an Appeal to the Laws of Dynamics," by F. R. 

 Moulton, Astrophysieal Jouriuil, March, 1909, pp. 

 103-130. 



^ " An Attempt to Test the Nebular Hypothesis 

 by the Relations of Masses and Momenta," by T. 

 C. Chamberlin, Jour. Ocol., Vol. VIII., January- 

 February, 1909, pp. 58-73. 



