CORRESPONDENCE 283 



and the soap to be slightly alkaline. Samples of faeces near 

 the bottles were neutral. 



The acids whose labels were eaten or gnawed are nitric, 

 hydrochloric, and sulphuric. 



The evidence seems to show that the rat had learned by 

 experience or accident, under its normal conditions, that the 

 food elements in the alkaline soap were slightly more palatable 

 when taken with a sip of neutralising acid. 



The older the rat the wiser he may become ! 



Yours very truly, 



Enoch Karrer. 



THE ICE-AGE QUESTION 



I. — From Major R. A. Marriott, D.S.O. 



Dear Sir, — The remarks made by Mr. H. Spencer Jones under 

 this heading, in the July number of Science Progress, appear 

 to be an attempt to shelve rather than to solve this very 

 important question. The evidence in favour of Drayson has 

 now reached a stage which makes it less than ever " not neces- 

 sary " for astronomers "to enter into the reasons for the 

 unanimous rejection " of Drayson's theory. 



Unfortunately, it is just these reasons that geologists and 

 laymen wish to know. But, if astronomers would answer this 

 one question satisfactorily, it would meet the requirements of 

 the case. If Drayson's reason for the continuous decrease of 

 the obliquity is rejected, what takes its place ? 



Is it due to the action of the planets which, until the claims 

 of Drayson were put forward lately, was considered to be wholly 

 negligible ? 1 Or to what ? If the curve followed is now better 

 known than when it was " for small angles a circle, but for 

 larger angles not a circle," 3 let us have it. 



The caution given against basing geological conclusions on 

 the theory is wholly unnecessary, since all the main and essential 



1 If due to the action of the planets, further questions under this head should 

 be able to be answered — viz., What is the different axis, and how long the 

 different period? (See SCIENCE PROGRESS, April 1919, p. 601.) 



* Statements made by astronomer-correspondents of Drayson's time, and 

 recently. 



