PLAN ETESIMAL THEORIES OP THE EARTEl's ORIGIN. 



189 



impossibilities of the existence and permanence of these unique 

 rings as either solid or liquid continuous bodies, wrote* : — 



" The sole hypothesis remains that the rings are composed of 

 flights of disconnected satellites, so small and so closely packed 

 that, at the immense distance to which Saturn is removed, they 

 appear to form a continuous mass." 



In other words the Saturnian rings are made up of 

 myriads of separately moving small masses, which are doubt- 

 less similar to the stony meteorites that fall rarely on the 

 earth. 



Again, the origin of the hundreds of asteroids, or minor 

 planets, mostly no more than a few miles in diameter, but 

 including several from 100 to perhaps about 300 miles in 

 diameter, seems very readily explained under this modification 

 of the nebular theory. 



Professor Young well saysf : — 



" The meteoric theory of a nebula does not in the least invalidate, 

 or even to any great extent modify, the reasoning of Laplace in 

 respect to the development of suns and systems from a gaseous 

 nebula. The old hypothesis has no quarrel with the new." 



Another theory, which diners more widely from that of 

 Laplace, has been very recently proposed by Professor T. C. 

 Chamberlin, of the University of Chicago, who names it the 

 Planetesimal Hypothesis. His studies in this direction have 

 been in progress about five years, with publication of preliminary 

 papers,^ preparing the way for the new hypothesis ; but its 

 first somewhat detailed statement in print has appeared since 

 the beginning of the present year.§ In this latest paper, 

 Professor Chamberlin gives the following principal outlines of 

 his researches for a new and more applicable nebular theory, 

 especially having in view its relation to the origin of the 

 earth. 



* Saturn and its System, second edition, revised, 1882, p. 135. 

 t Text-Book of General Astronomy, V- 526. 



% " An Attempt to Test the Nebular Hypothesis by the Eelations of 

 Masses and Momenta," in the Journal of Geology, Chicago, vol. viii, 

 pp. 58-73, Jan. -Feb., 1900. " On a possible Function of Disruptive 

 Approach in the Formation of Meteorites, Comets, and Nebulae, Journal 

 of Geology, vol. ix, pp. 369-392, July-August, 1901. 



§ " Fundamental Problems of Geology," in Year Bool', No. 3, for 



1904, of the Carnegie Institution of Washington, published in January, 



1905, pp. 195-258. 



