470 Mr. J. Russell on the Superposition of 



importance. Both experimental methods were adopted, and: 

 are as follows : — 



A. Mechanical vibrations are superposed upon constant 



field. 



B. A change of field is superposed upon mechanical vibra- 



tions permanently acting. 



These methods are fully described in the paper. Suffice 

 it to say here that, under the A conditions, mechanical 

 vibrations are superposed by simply ringing the electric bell. 

 This necessitates that demagnetization by decreasing reversals 

 must follow upon every superposition of vibrations, before 

 the next observations are made. Under the B conditions, on 

 the other hand, the bell is rung after demagnetization, and con- 

 tinues ringing until any set of readings has been completed. 



Intensity of Vibrations varied. — Figs. I. & n. (PL XI.) show 

 for annealed iron, and for one value of field at cyclic extremes, 

 11 = 0*92, the experimental results under the A and B con- 

 ditions respectively, for three different intensities of vibrations 

 obtained by suitably altering the voltage at the terminals of 

 the electric bell. The normal loops without vibrations are 

 the same in both cases. The other curves show the effect of 

 increasing the intensity of vibrations in the ascending order 

 indicated by the numerals 1, 2, and 3. A glance at the 

 curves shows that the order of superposition under the A 

 and B conditions produces apparently very different results. 

 Note that the horizontal and vertical ordinates H and B are 

 in O.G.S. units in all the diagrams. 



Intensity of Vibrations constant. — In the experiments now 

 to be described the strongest vibrational intensity, corre- 

 sponding to curves 3 of figs. I. and n., is used. 



Permeability and Retentivity Diagrams. — Figs. III. and iv. 

 show for annealed steel and nickel, and tigs. vin. and ix. for 

 quenched steel and nickel, BH curves, and curves of residual 

 magnetization (likewise plotted against H), obtained by with- 

 drawing the field at all values of induction measured. The 

 full and faint dotted and continuous lines are the induction 

 and residual magnetization curves respectively, with and 

 without permanently acting vibrations (B conditions). The 

 full and faint dash lines show the ratios B v /B and 

 B v — R v /B — R respectively for all values of H. B v , R v and 

 B, R signify the induction and residual magnetization with 

 and without vibrations respectively. The values of these 

 ratio ordinates are to the left of the diagrams and are to the 

 same scale throughout. The different scales to which H and 

 B are drawn should be noted when comparison is made 

 between these figures. 



