21 



EEMARKS ON SIE ROBEET BALL'S PAPEE (EEAD 

 AT THE HOBAET MEETING OF THE AUSTEAL- 

 ASIAN SCIENCE ASSOCIATION), ENTITLED : 

 " THE ASTEONOMICAL EXPLANATION OF A 

 GLACIAL PEEIOD." 



By a. B. Biggs. 



Of the many interesting papers that were read in the 

 Astronomical Section of the recent Science Cougress, by far 

 the most interesting tome, and probably to the majority of 

 those who listened to it, was that with which we were 

 favoured by Sir Eobert Ball, and which was read by His 

 Excellency, Sir Eobert Hamilton. 



In the paper referred to. Sir John Herschel is accused by 

 the author of having made, in his " Outlines of Astronomy," 

 *' a curiously erroneous statement :" that " Herschel wrote 

 down hastily a statement which was quite wrong," and that 

 Croll and others had been misled by Herschel's mistake. 



It was startling to me to find two men of such eminence 

 in Astronomical Science at variance with reference to a com- 

 paratively simple astronomical fact. Sir Eobert Ball 

 announces, as the object of his paper, " to indicate clearly 

 the character of the error . . . and to substitute for it 

 the correct mathematical theory." So that he is v^ery 

 emphatic upon the subject of the supposed mistake. 



I did not feel myself in a position to criticise the paper at 

 its reading, even had I the temerity to attempt it. I needed 

 to study it at leisure before venturing on so bold a step. The 

 receipt of a copy from the General Secretary of the associa- 

 tion has put me in a position to look into the matter mor& 

 closely. 



The purport of Sir Eobert Ball's paper is to show that the 

 successive periods of glaciation, alternating with periods of 

 genial or tropical temperature, which geologists infer from 

 the indications of the rocks and strata, are a necessary 

 corollary from astronomical data. It will be well then, as a 

 preliminary, to state as concisely and clearly as I possibly 

 can what are the conditions of the problem, which I take 

 to be the following, every one of which is essential to the 

 conclusion arrived at : — 



1. That the earth's orbit is not a circle, but an ellipse, the 

 sun's position in relation thereto being, not in the centre, but 

 in one of the foci of the curve ; consequently there are two 

 opposite points at which respectively the earth is nearest to, 



