., RECENT COSMOGONIES 249 



inherent motions, but on account of their mutual attrac- 

 tion, the energy of their resulting critical velocities, di- 

 rected, by Newton's second law, toward their respective 

 centers, would bear to the energy of their proper-motion 

 velocities (based on the known value of the sun's) a ratio 

 of something like 500 2 to 12 2 , or 1,600 to 1, thus ensuring 

 total and not partial impact, thereby completely invali- 

 dating Professor Bickerton's hypothesis in its very es- 

 sence. 



THE PLANETESIMAL HYPOTHESIS 



There are two hinges to the cosmological shutter 

 astronomy and geology. In order to make it swing easily 

 both ways, it is not only necessary that the facts of as- 

 tronomy be successfully correlated with one another, and 

 the facts of geology with one another, but both of these 

 sets of facts must likewise be mutually coordinated. 

 Nearly a score of years ago Doctor Thomas Chrowder 

 Chamberlin, who for the past quarter-century has been 

 dean of the scientific faculty of the University of Chicago, 

 undertook to construct a system of cosmology from a 

 geologist's point of view. His researches along this line 

 have been summed "p in his recent work, The Origin of 

 the Earth; and the name which he gives his theory is, 

 The Planetesimal Hypothesis. 



Now, there are two fundamental astronomical condi- 

 tions that especially concern geologists which must posi- 

 tively be supplied by any cosmological theory before it 

 can prove acceptable, and both of these concern the sun. 

 These conditions are, first, that a source of heat be found 

 capable of maintaining him at practically an even aver- 

 age temperature over a period of the order of a thousand 

 million years, and, second, that the source so found shall 

 consistently explain the alternation of ice- and genial ages 

 which have occurred in the course of the earth's geologi- 

 cal history. 



On the first of these problems Doctor Chamberlin 

 does not, nor does he try to, throw any new light, but his 

 chief aim is avowedly to explain the alternation of the 



