THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FIFTH SBEIES.] 



FEBRUARY 1884. 



XII. Examination of Mr. Alfred R. Wallace's Modification of 

 the Physical Theory of Secular Changes of Climate* By 

 James Croll, LL.D., F.R.S.* 



ON the publication of _ Island Life/ upwards of three years 

 ago, the author kindly favoured me with a copy. He 

 at the same time wrote to me stating that the volume contained 

 some modifications of my theory of secalar changes of climate, 

 to which he had been led by a careful consideration of the 

 subject, and that he would be glad to have an expression of 

 my opinion in regard to his results. Deeply interested as I, 

 of course, felt in the matter, I was however compelled, owing 

 to the state of my health, to leave the volume unread till 

 within the last few months. This fact will account for the 

 appearance of the following remarks at this somewhat late 

 date. 



I have read the chapters relating to Geological Climate with 

 the greatest amount of interest and pleasure, and have to thank 

 the author for his very clear and able exposition and defence 

 of the main points of my theory. It appears to me, however, 

 that what Mr. Wallace regards as modifications are in some 

 cases really necessary parts of the theory. These may not, 

 it is true, have been in all cases expressed by me, but they 

 are nevertheless implied in the theory. Other points, again, 

 regarded as modifications are simply facts lying altogether 

 outside of the theory, which can in no way affect it. With 



* Communicated by the Author. 

 Phil. Mag. S. 5. Vol. 17. No. 104. Feb. 1884. G 



