12 MR. H. TOML1NSON ON THE INFLUENCE OF STRESS AND 



i 



Logarithmic decrement due Ditto when the magnelifl- 

 to internal friction when ing stress Tag alwayn 

 the magnetising stress applied in the game 



wag reversed, direction. 



017416 -0064C4 



The effect in the former of the two cases is very much greater than in the latter, 

 and this might have been anticipated, for the change of magnetisation with each 

 reversal is much greater than that produced by each repetition of the stress. No 

 doubt the difference in the effects in the two cases would be proportionately still 

 greater for a lower value of magnetic stress, for, with this particular specimen of iron, 

 when the magnetising stress was about 4 C.G.S. units, the change of magnetisation 

 produced by each reversal was from eighteen to twenty times as great as the change 

 produced by each repetition of the stress.] 



It has been remarked that when the amplitudes of the vibrating wire are such as only 

 to produce very small molecular displacements neither the internal friction nor the 

 torsional elasticity is sensibly affected by sustained magnetisation. Since, however, 

 the author's investigations, mentioned in the outset of this memoir, and in which the 

 wire had been vibrated through comparatively large arcs, seemed to show that 

 magnetism did slightly affect the torsional elasticity, he proceeded to re-try some of 

 his old experiments relating to the effect of magnetisation on torsional elasticity, and 

 at the same time also to study the alteration of internal friction which might ensue 

 with large amplitudes of vibration. 



Experiment XI. 



The mirror was twisted round through an angle of 18, then refixed ; afterwards 

 the vibrator was twisted so as to bring the reflected spot of light just on to one end 

 of the scale ; the vibrator was then let go, and as soon as the subsidence of the 

 amplitude had caused the spot of light to reach the division on the scale marked 100,* 

 or thereabouts, readings were taken. For the battery power 10 GROVE'S cells were 

 used, and the magnetising stress was very nearly 35 in electromagnetic units. 



> The zero of the scale was, in this instance, at the end of the scale from which the vibrator was 

 started, so that as the amplitudes of the vibrations subsided the readings increased. 



