302 Effect of a Longitudinal Magnetic Field on Internal Viscosity 



effects are much smaller. The curves for higher fields moved con- 

 tinually to the right, and showed no tendency to become coincident. 



In both iron and steel the logarithmic decrements, as the curves 

 show, were much more nearly constant throughout each curve than 

 was the case for nickel. In steel the decrement fell off rapidly at first, 

 so that throughout the greater part of the curve it was nearly con- 

 stant at a distinctly smaller value than at the beginning of the curve. 



Experiments were also made with a view to ascertaining whether 

 the change in the physical properties of the wires produced by drawing 

 them through a draw-plate altered in any way the effects of magnetisa- 

 tion on the rate of subsidence. In the case of drawn nickel wire the 

 most striking alteration was the disappearance of the reversal of the 

 effect of magnetisation. The magnetisation increased slightly the rate 

 of subsidence, and this increase continued quite regular to the highest 

 values of the field obtainable (about 400 C.G.S.), no critical value of 

 the field similar to that observed for the undrawn wire being obtained. 

 In the case of drawn iron, on the other hand, the effect of magnetisa- 

 tion was to regularly diminish the rate of subsidence. The effect was 

 thus similar to that obtained for the undrawn wire, the chief point of 

 difference being that, in the case of the drawn wire, further increase 

 of the field gave farther perceptible diminution in the rate of subsi- 

 dence, so that there was not that approximation to constancy of effect 

 of field, apparently depending on magnetic saturation, which was 

 observed in the case of the undrawn wire. The drawing of the wires 

 was found to result in a considerable increase of their rigidity. 



As a check upon the experiments detailed above, a copper wire was 

 substituted for the iron or nickel wire along the axis of the coil, and a 

 field of 230 C.G-.S. units was applied. No perceptible effect upon the 

 rate of subsidence was found to be produced. 



[Note, added May 30, 1902. — The effect of annealing the nickel wire 

 which had been hardened by drawing has now been observed. The 

 wire was heated to a bright red heat and then suddenly cooled by 

 being plunged into water. It was found that the wire had returned 

 to its former state, as all the features of the curves of Diagram II were 

 again observed, with the difference that the curve of maximum rate of 

 subsidence occurred with a field of only about half the former value. 

 Experiments on the effect of annealing the iron wires are in progress, 

 and show that the effect of annealing, by heating and slow cooling, is 

 to annul the change produced by drawing.] 



