496 MR JAMES RUSSELL ON THE SUPERPOSITION OF MECHANICAL VIBRATIONS 



first is the B — H hysteresis loop determined by what is virtually Ewing's method of 

 single steps from a maximum. The second measures the instantaneous change of 

 induction which takes place when mechanical vibrations are superposed at any and all 

 stages of the normal cycle. 



Experimental Methods under B Conditions. 



After demagnetisation as before, the mechanical vibrations are put on. They 

 remain " on " until any set of readings has been completed. Under these conditions 

 the usual curves showing either the relationship between H and B or the B — H hysteresis 

 loops are determined, as the case may be. In the former case, one-half the average 

 induction change on the 30th and 31st reversals determines the value of B, commencing 

 in the usual way with the lowest values of H, and finishing with the highest. In the 

 latter case, the loops are determined by what is now exactly Ewing's method of single 

 steps from a fixed maximum. The area enclosed by this loop, like the normal cycle 

 above described, and with which it is compared, measures the energy loss per cycle, when 

 the properties of the magnetic metal are altered by permanently acting mechanical 

 vibrations. It is hardly necessary to point out that the loop delineating the instan- 

 taneous changes due to superposed vibrations under the A conditions does not do so. 



Diagrams. 



The experimental results are shown in the diagrams. The abscissae are in all cases 

 values of H in C.G.S. units. The ordinate values of B are likewise in C.G.S. units. In 

 those figs. (III., IV., V., XII., XIII., XIV.) where ratio ordinates also occur, the ratio 

 values are on the left, those of B on the right. 



It was found, on plotting the diagrams, that the observations with vibrations fell as 

 readily into line as when no vibrations were acting. When the fields are cyclic, each 

 arm of the loops is obtained by plotting the average readings taken on both arms. 

 This secures symmetry of the diagrams in reference to the origin. 



Intensity of Vibrations, Varied. 



The intensity of the vibrations could be increased by increasing the voltage at 

 the terminals of the electric bell. When the voltage was too great, the fundamental 

 note of the bell was entirely lost in the louder rattle of the hammer, and the tingling 

 sensation felt by the fingers on touching the vibrating wire was markedly reduced. In 

 the following experiments the musical note of the gong was not overpowered in this 

 way even with the highest voltage used. 



Figs. I. and II. show, for annealed iron and for one low value of field (H = 0*92), the 

 cyclic results obtained under the A and B conditions respectively, for three different in- 



