PROCEEDINGS OF SECTIONS. 



^ 



Section A.. 



ASTRONOMY, MATHEMATICS, PHYSICS, AND 

 MECHANICS. 



Prbsiden't of the Section : 



W. H. BRAGG, M.A., Professor of Mathematics. University 

 Adelaide, S.A. 



1.— THE ASTRONOMICAL EXPLANATION OF A 

 GLACIAL PERIOD. 



By SIR ROBERT BALL, Astronomer Royal of Ireland. 



It lias been often suggested that there might be some astro- 

 nomical explanation of that remarkable period in the earth's 

 history which geologists designate as glacial. Indeed, it is 

 doubtless known to the members of this Association that the 

 late Dr. Croll discussed the subject at much length in his 

 ingenious work entitled Climate and Time. I liave recently 

 undertaken the investigation of the astronomical foundation 

 of the theory at which Croll has laboured. I found, much 

 to my surprise, that this capable geologist was quite 

 unacquainted with the true astronomical doctrine on the sub- 

 ject. He had been doubtless misled by a strange passage in 

 Sir John Herschel's well-known book The Oiif/ines of 

 Astronomy . It seems that this eminent astronomer made a 

 curiously erroneous statement in a matter bearing directly on 

 the causes of glaciation. It was perhaps not unnatural for 

 other wM'iters to accept without question a proposition of a 

 mathematical character when it seemed to be authenticated 

 by so illustrious a name as that of Herschel. Anyone, how- 

 ever, who possesses sufficient mathematical knowledge will 

 be able to convince himself that Herschel wrote down hastily 

 a statement which was quite wrong. There is not the least 

 doubt that Herschel himself would have readily admitted 



