it;'.- 



'\^L.v. 





SCIENCE PROGRESS 



IN THE TWENTIETH CENTURY 



A QUARTERLY JOURNAL OF 



SCIENTIFIC WORK 



& THOUGHT 



NO. 20. APRIL 191 1 



EDITORS 



H. E. ARMSTRONG, Ph.D., LL.D., F.R.S. 

 J. BRETLAND FARMER, M.A., D.Sc, F.R.S. 

 W. G. FREEMAN, B.Sc, A.R.C.S., F.L.S. 



LONDON 

 JOHN MURRAY, ALBEMARLE STREET, W. 



191 1 



Price Bj- net 



VOL. V 



