CHANGE OF ELASTIC CONSTANTS OF FERROMAGNETICS. 9 



above tlie desceiulinp; one. In the following tables, the length 

 changes iintler constant tension arc results for the stage of in- 

 creasing weights, taken after several cycles of loading and un- 

 loading.- The usual processes of observation were followed. The 

 wire was lirst loaded with the smallest weight, which was generally 

 1 kilogram ; the demagnetization by reversals was then carefully 

 effected. A series of gradually increasing currents was passed 

 through the magnetizing coil, and the corresponding deflections 

 of the scale were noted. The wire was then completely demag- 

 netized, and the zero position of the scale tested. Another weight 

 of 1 kilogram was added and demagnetized, and the same processes 

 were repeated. In this \Yay, a set of observations corresponding 

 to the different weights was taken. 



The change of elasticity was next measured. We applied an 

 initial load to the pan, demagnetized the wire l)y reversals, added 

 and removed a weight of 1 kilogram, and adjusted the compen- 

 sation, until the deflection due to the additional weight was as 

 small as possible. The demagnetization was then carefully effected. 

 The small deflection due to the additional weight for no field was 

 recorded. Then we applied a magnetizing field and observed the 

 deflection due to the additional weight. After the demagnetiza- 

 tion, the deflection due to the same load for no field was again 

 tested. The difference between the two deflections for no field 

 and for the magnetic field gives the change of elasticitv due to 

 magnetization, provided we know the total elongation caused by 

 the additional weight of 1 kilogram. To avoid any accidental 

 eiror in observing these deflections, the deflections for several 

 cycles of loading and unloading were, in each case, recorded, and 

 their mean was taken. The initial w^eigbt was next increased. 



