1904] Magnetic Field on Torsional Oscillations, etc. 291 



Curve VII was obtained. The light vibrator and the heavy one were 

 then used again in succession and gave curves VIII and IX. Probably 

 the difference between curves VIII and IX was due to the additional 

 longitudinal strain (in this case temporary) given to the wire by the 

 additional load. The subsidences were taken for all the curves after 

 forty vibrations no matter which vibrator was used. 



The difference between curves VII and IX, it will be noticed, is a 

 twofold one ; a much greater maximum of effect and a shifting of the 

 maximum to a greater field. 



It seems not impossible that the main differences between nickel and 

 iron disclosed by the experiments described in the previous paper, and 

 the effects now discussed, may be explained by supposing that the 

 groups of magnetic molecules in nickel lie in layers across the wire, 

 separated by a matrix of conducting material which becomes hardened 

 by drawing, and prevents the progressive changes in the groups from 

 the initial condition of closed chains, which is brought about by 

 magnetic force. On the other hand, the supposition would be that in 

 iron the molecular magnets are in longitudinal groups with non- 

 magnetic material between. Thus, in the vibrating wire in the first 

 case, the conducting material moving in the field of the molecules 

 would give rise to dissipation of energy, and there would be a greater 

 rate of subsidence in the field than without it. 



In the other case it is conceivable that the changes of the longitudinal 

 and initially more or less nearly closed chains might result in such a 

 modification of field as to result in less dissipation of energy by 

 induction currents due to relative motion of the conducting substance 

 and the molecular magnets, for the conducting matter between the 

 longitudinal rows of elementary magnets may move in a feebler field 

 after the magnetisation than before, owing to the breaking-up of the 

 closed chains. 



The effect of permanent and temporary longitudinal strain in nickel 

 seems contrary to what we should have expected. It is known that 

 longitudinal strain on nickel diminishes its longitudinal magnetisation, 

 and judging from this we should have rather expected the contrary 

 effect to that which we have observed. There is however, no doubt as 

 to the result, which is borne out by many sets of observations. The 

 cause must be matter for further consideration and experiment. 



