1895.] 



President's Address. 



121 



Royal Medal. 

 Professor James Alfred Ewing, F.R.S. 



A Royal Medal is conferred on Professor J. A. Ewing for his in- 

 vestigations on Magnetic Indnction in Iron and other Metals. 



The magnetic properties of iron and steel when subjected to mag- 

 netising forces of different intensities, under various conditions of 

 temperature and mechanical stress, have been studied by many 

 physicists both in this country and abroad. In a series of papers 

 which have appeared at intervals during the last fourteen years, 

 Professor Ewing has put on record a remarkable collection of experi- 

 mental facts connected with these complicated subjects. In some of 

 his results and methods he was anticipated by others, but apart from 

 the wide extent of his investigations, he has displayed great sagacity 

 and originality both in his more fundamental researches, and in the 

 directions in which he has developed his work. 



Having studied the behaviour of iron when subject to magnetic 

 forces which vary in a cycle, he applied the same process to nickel, 

 proving that, as in the case of iron, the susceptibility is constant for 

 small forces, but that the range of force over which this law holds 

 good is much larger for nickel than for iron. 



Professor Ewing has also investigated the behaviour of iron and 

 steel of various qualities, of manganese steel, of cobalt and nickel, 

 w T hen placed in very strong magnetic fields, the intensity of which 

 was raised to the splendid magnitude of 25,000 C.Gr.S. units in the 

 air around the metal bar under observation, thereby producing an 

 "induction " of over 45,000 within the bar, when the bar was iron. 

 He showed experimentally, in corroboratiou and extension of Joule's 

 primary discovery for iron, that in iron, nickel, and cobalt, the 

 intensity of magnetisation approaches asymptotically towards a 

 limiting value, which it very nearly reaches before the magnetising 

 force attains a comparatively small magnitude, and at w-hich it 

 remains constant while the magnetising force is increased without 

 limit. 



Not content with investigations such as these, Professor Ewing 

 has made an important advance in our knowledge of the probable 

 constitution of magnetic substances. He constructed a model of 

 such bodies by placing a number of small magnets near to each 

 other so that each is free to rotate in a horizontal plane. These 

 magnets, when disturbed, settled down into groups of more or less 

 stable equilibrium, which are gradually broken up under the in- 

 fluence of increasing magnetic forces. This model suggests the 

 novel and most important conclusion that the act of magnetisation 

 is accompanied by the re- arrangement of similar groups of magnetic 

 molecules. So closely does it reproduce the behaviour of iron, that 



VOL. LIX. k 



