PBESIDENTIAL ADDRESS — SECTION A. 35 



Professor Ewing sets out, and he arrived at his theory by 

 making a large number of Httle magnets, mounting them on 

 pivots on a horizontal plane, and arranging them in groups, so 

 that they may on a large scale represent the molecules Nvithin 

 a magnetic body. These little needles are, of course, subject 

 to their own mutual actions. Professor Ewing, by surround- 

 ing them with a large wire spiral through which an electric 

 current could be sent, could subject them to the action of a 

 magnetic field of any intensity, and at the same time have a 

 direct view of how they behaved. He found that with the 

 rough model of a magnetic body that I have described he 

 was able to imitate much of the known behaviour of magnetic 

 substances. With no magnetizing force acting on them they 

 arranged themselves in equilibrium under their own mutual 

 actions, and exerted no external action. With small magnetiz- 

 ing current they are a little deflected from their mutual equili- 

 brium position, and the system acquires a small magnetic 

 moment. If the magnetizing force be removed they return to 

 their former positions. If larger forces be applied, some of the 

 little magnets are so far deflected that, reaching a position of 

 unstable equilibrium, they will turn farther round, and, having 

 done so, they will remain in a new position of equilibrium even 

 when the magnetizing force is removed. The system will thus 

 have acquired a permanent magnetic moment, or, in other 

 words, will have become permanently magnetized. Finally, 

 when a very large magnetizing force is applied, the small 

 needles will all place themselves approximately in alignment 

 with that force, and so the maximum amount of magnetic 

 moment will be acquired by the system, or, in other words, 

 the point of saturation will have been reached. Hysteresis, 

 the effects of temperature stress and mechanical vibration, can 

 all be easily imitated with this model. The theory of mag- 

 netism, so deduced by Ewing, may be stated thus : The mole- 

 cules of a magnetic body are magnets, they are free to turn 

 about, and they mutually act on each other. 



Turning now to the practical applications of science that 

 have rendered social economy so different nowadays from what 

 it was half a century ago, I find that the field is so extended 

 that the most I can do is to briefly direct your attention to one 

 or two of them that may possibly interest you. 



Electricity of course leads the van, and of some of its 

 applications alone will I speak. 



So much has been said and written about electric ligliting 

 that I need scarcely do more than mention it. Tiie fact that 

 all London will shortly be supplied, both in streets and houses, 

 with the electric light, says enough lor its progress as a com- 

 mercial undertaking. 



The introduction within the last few years of the three-wire 



