232 Professor J. A. Ewing on Hysteresis, [May 22, 



actually reduced. Indeed, by a small further increase of the field 

 the hysteresis could be made to practically vanish. This very 

 curious result had been predicted originally by Mr. James Swinburne, 

 as a consequence of the lecturer's theory, and had at that time seemed 

 so unlikely that it was urged as an objection to the theory. It had 

 now been proved to afford the theory the strongest possible con- 

 firmation. 



A model was shown in illustration of this point, in which a glass 

 plate carrying a number of small pivoted magnets (Fig. 6) was made 

 to revolve slowly in a magnetic field produced by two neighbouring 

 coils. So long as the field was weak the small magnets formed 

 groups which were broken up during the revolution, thereby dis- 

 sipating energy and exhibiting hysteresis ; but when the field was 

 sufficiently strengthened the small magnets continued to point one 

 way without forming groups, for their mutual magnetic forces were 

 then masked by the external or field force. There were consequently 

 then no unstable phases in the motion and no hysteresis. 



Hysteresis in the magnetic quality of iron was to be ascribed to 

 the formation of stable groups of molecules, in consequence of the 

 mutual forces which the molecules exerted on one another in virtue 

 of their magnetic polarity. It might very well be that in other 

 manifestations of hysteresis, such, for example, as the familiar 

 phenomenon of friction between two solid surfaces when rubbing 

 against one another, the resistance and consequent dissipation of 

 energy were similarly due to the forming and breaking up of molecular 

 groups, the molcules being mutually constrained by some other 

 species of polar forces, possibly due to electrostatic charges upon 

 them. 



[J. A. E.] 



