Elasticity of Ferromagnetic Substances by Magnetization. 63 



the coefficient of rigidity for different fields from the periods 

 of oscillation. The wires tested were the same as those used 

 in the above experiment for the change of elasticity. The 

 wire was hung vertically in the field of the magnetizing coils 

 used in the previous experiment. Its upper end was brazed 

 to a rigid brass rod, which was clamped to the frame above. 

 To the lower end a similar rod was brazed, to which the 

 oscillatino- weights were fixed. In order to sufficiently 

 diminish the disturbance due to the resistance of air, 

 Foueault currents &c«, the period of oscillation was made 

 very long by using a weight with considerable moment of 

 inertia. °A rectangular brass bar (42*80 x 0"S95 x 1/946 cm. 3 ) 

 was fixed horizontally to the lower end of the lower rod, at 

 its middle point. Two equal cylindrical weights (each 657 gr.) 

 made of lead could be fixed symmetrically on the bar at any 

 desired distance from the middle. Besides, two equal 

 cylindrical weights (1671 and 1610 gr.) of lead could be pat 

 on the bar with their axes coinciding with that of the rod. 

 Suitable combinations of these different weights enabled us 

 to adjust the periods o£ oscil'ations for different tensions to 

 convenient values. A light mirror was fixed to the lower 

 rod. The image of a horizontal scale placed in front of the 

 arrangement was observed with a telescope in the usual 

 manner. 



To start the torsional oscillation of the wire, a lead tube 

 was directel to one end of the horizontal bar. The tube 

 ooino- to the observer was held by his hand ; the oscillation 

 was started by blowing through the tube, while observing 

 through the telescope. The amplitude of the oscillation 

 could be increased or diminished at will, by blowing with 

 suitable force on the bar in a suitable phase of its oscillation. 

 In this way, the equality of the amplitude could easily be 

 effected within 1 mm. of the scale. It was usually 5 cm. 

 with a scale distance of 1*46 m.. which corresponds to an 

 amplitude of about 1°. 



It was necessary to protect the oscillating system from 

 disturbance due to air-currents. 



Our procedure was as follows : — The wire to be tested was 

 first demagnetized by reversals, the zero of the scale set to 

 the position of equilibrium ; a field was applied, and then 

 oscillation started. Care was taken to adjust the amplitude 

 for different fields so as to make them as equal as possible. 

 in order that in the comparison of periods for different field.-, 

 the effects of amplitudes might be neglected. One of the 

 observers signalled at each complete oscillation, while the 



