ESSAY-REVIEWS 67 



fessorship, and which he had before his death desired to see 

 published, have been included in this volume. Hill's work 

 greatly interested Darwin, and in this course of lectures he 

 treats it very clearly and makes the essential features easy to 

 grasp. As an introduction to a study of Hill's work or as a 

 means of obtaining a general knowledge of it without having 

 to go through the full details of the original, it may confidently 

 be recommended. Of Darwin as a teacher Prof. Brown speaks 

 in very appreciative terms : 



11 To the pupils who owed their first inspiration to him he 

 was a constant friend. First meeting them at his courses on 

 some geographical or astronomical subject he soon dropped 

 the formality of the lecture room and they found themselves 

 before long going to see him continually in the study at Newn- 

 ham Grange. . . . To have spent an hour or two with him, 

 whether in discussion on ' shop ' or in general conversation, 

 was always a lasting inspiration. And the personal attachment 

 of his friends was strong ; the gap caused by his death was 

 felt to be far more than a loss to scientific progress. Not 

 only the solid achievements contained in his published papers, 

 but the spirit of his work and the example of his life will live as 

 an enduring memorial of him." 



That power of stimulating thought, which Darwin had so 

 well, is the true function of a teacher and one which unfor- 

 tunately too many University professors lack. It may well be 

 that it will ultimately be recognised that our greatest debt 

 to Darwin is to be found not in his own researches, important 

 though these are, but in the researches of some of his pupils 

 who owed their initial stimulus to him. 

 Royal Observatory, Greenwich. 



THE ORIGIN OP IGNEOUS HOCKS, by Arthur Holmes, D.I.C., 

 A.R.C.S., B.Sc, F.G.S. : on The Later Stages of the Evolution of the 

 Igneous Rocks, by N. L. Bowen. Supplement to the Journal of 

 Geology, vol. xxiii. pp. 1-91, 1915. 



During recent years a great deal of attention has been given 

 by petrologists to the difficult but fascinating problem of the 

 origin of igneous rocks. The relative claims of differentiation 

 alone, and of differentiation combined with assimilation, have 

 been ably expressed by Harker, Iddings, and Daly. These 



