Illustrations xvii 



FACING 

 PAGE 



THE POLAR BEAR OF THE FAR NORTH ....... 227 



Photo: W. S. Berridge. 



AN ALLIGATOR "YAWNING" IN EXPECTATION OF FOOD .... 227 



From the Smithsonian Report, 1914. 



BABY ORANG 232 



Photo: W. P. Dando. 



ORANG-UTAN 232 



Photo: Gambier Bolton. 



CHIMPANZEE ............ 233 



Photo: James's Press Agency. 



BABY ORANG-UTAN .......... 233 



Photo: James's Press Agency. 



ORANG-UTAN ........... 233 



Photo: James's Press Agency. 



BABY CHIMPANZEES .......... 233 



Photo: James's Press Agency. 



CHIMPANZEE ............ 288 



Photo: W. P. Dando. 



YOUNG CHEETAHS, OR HUNTING LEOPARDS ...... 238 



Photo: W. S. Berridge. 



COMMON OTTER ........... 239 



Photo: C. Reid. 



SIR ERNEST RUTHERFORD ......... 246 



Photo: Elliott & Fry. 



J. CLERK-MAXWELL 246 



Photo: Rischgitz Collection. 



SIR WILLIAM CROOKES .......... 247 



Photo: Ernest H. Mills. 



PROFESSOR SIR W. H. BRAGG . . . . . . . 247 



Photo: Photo Press. 



COMPARATIVE SIZES OF MOLECULES ....... 250 



INCONCEIVABLE NUMBERS AND INCONCEIVABLY SMALL PARTICLES . . 250 



WHAT is A MILLION? .......... 250 



THE BROWNIAN MOVEMENT ......... 251 



A SOAP BUBBLE (Coloured Illustration) ...... 252 



Reproduced from The Forces of Nature (Messrs. Macmillan). 



