SECTIONAL TRANSACTIONS. 



SECTION A. 

 MATHEMATICAL AND PHYSICAL SCIENCES. 



Thursday, September 10. 



Discussion on The evolution of the Solar System (io.o). 



Sir James Jeans, F.R.S. — The evolution of the Solar System. 



Hypotheses as to the origin of the Solar System may be classified accord- 

 ing to the number of stars which were concerned in the birth of the planets. 

 Pre-eminent in the category of solitary-star theories is the Nebular Hypo- 

 thesis of Laplace, which is now out of favour because it fails to satisfy certain 

 numerical tests. To the category in which two stars are involved belong 

 the Planetesimal Hypothesis of Chamber lin and Moulton, various forms of 

 tidal theory, and the collision theory of Bickerton which has been recently 

 rejuvenated by Jeffreys. In the three-star category comes the recent theory 

 of Lyttleton, according to which the planets resulted from an encounter 

 between a single star and a binary. 



These various theories can be checked and tested by the general principles 

 of dynamics, particularly that of ' conservation of angular momentum,' 

 as also by certain principles of an even more general kind. 



Prof. Arthur Holmes. — Geological time and former glaciations in 

 relation to the evolution of the Solar System. 



The work of Paneth on the helium-ratios of iron meteorites suggests an 

 age of the order 2,800 million years for the solar system. Of the rocks of 

 the earth's crust the oldest so far recognised have been found in South 

 Dakota (Black Hills) and Manitoba (east of Lake Winnipeg). The down- 

 ward sequences, with ages determined by the lead-ratio method, are as 

 follows : 



Black Hills, South Dakota. South-East Manitoba. 



Harney Peak Granite (1,500 ± 40 Peridotite — Appinite — Granite — 



million years). Pegmatite Intrusions (1,750 mil- 



(?) Lead System. lion years). 



Game Lodge Granite (1,820 ± 70 Rice Lake System : 



million years). Wanipigow phase : Quartzite, grey- 



Estes System : Quartzite and con- wacke, arkose, slate. 



glomerate with iron-formation, Beresford Lake phase : mainly vol- 



slate and green schist. canic. 



