I1ST THE LAST HALF-CENTURY. 29 



sequent events, there are numerous excel- 

 lent summaries of the progress of various 

 branches of science, especially up to 1881, 

 which was the jubilee year of the British 

 Association.* And, with respect to the 

 biological sciences, with some parts of 

 which my studies have familiarised me, 

 my personal experience nearly coincides 

 with the preceding half-century. I may 

 hope, therefore, that my chance of escap- 

 ing serious errors is as good as that of 

 anyone else, who might have been per- 

 suaded to undertake the somewhat peri- 

 lous enterprise in which I find myself 

 engaged. 



There is yet another prefatory remark 

 which it seems desirable I should make. 

 It is that I think it proper to confine my- 

 self to the work done, without saying any- 



* I am particularly indebted to my friend and col- 

 league Professor "Rilcker, F. R. S., for the many acute 

 criticisms and suggestions on my remarks respecting 

 the ultimate problems of physics, with which he has 

 favored me, and by which I have greatly profited. 



