108 C. Barns — Apparent Hysteresis. 



viscous effect has vanished and the result is simply increased 

 rigidity in definite amount during the continuance of each 

 magnetization. 



In figures 8, 9, and the corresponding figures 12, 13, 14, 15 

 (cf. the zigzag curves c), i. e., at low strains, 45° and 90°, the 

 viscous effect preponderates. On first making the current 

 after a fresh twist, rigidity is decreased ; on breaking it rigidity 

 is further decreased by a greater amount ; on again making 

 the current rigidity is increased definitely and the same occurs 

 after all subsequent magnetizations. 



In figures 10, 11, and 16, 17, the increased rigidity pre- 

 ponderates after the first magnetization. There is increased 

 rigidity on first making the current, a numerically larger 

 decrement on breaking, and thereafter definite increments of 

 rigidity during the continuance of each subsequent making of 

 the magnetizing current. Thus it follows that the magnetic 

 increment of rigidity increases and decreases faster than the 

 coexisting decrement of viscosity due to the first magnetiza- 

 tion. 



So understood, moreover, the observed hysteresis is a mechan- 

 ical phenomenon and the magnetization acts as does ordinarily 

 heat in producing the instabilities essential to viscous deforma- 

 tion. The molecular shake-up due to magnetic action is 

 practically instantaneous, whereas the heat motion within the 

 body is gradual in its action : hence the kaleidoscopic dis- 

 placement of molecules in the one case seemingly without 

 resistance, and the viscous displacement of molecules in the 

 thermal case (seemingly with resistance). Again the displace- 

 ment of the zero if due to viscosity should under like circum- 

 stances be of about the same order both in the cases of 

 longitudinal and of circular magnetization (aside from the heat 

 effect in the latter, which makes it larger). A comparison of 

 figures 3' to 6', with the subsequent figures 7 to 17 show dis- 

 placements of about the same order for both. 



11. Simpler in its nature is the evidence contained in figures 

 18-20, for the displacement of the zero after the first mag- 

 netization. If the wire is twisted to say 360° and back again 

 to zero, the resulting strain does not correspond to the zero of 

 stress. Certain configurations lag behind in the direction of 

 the twist which has last acted. The first magnetization, how- 

 ever, produces the necessary molecular shake-up to bring the 

 strain back again to zero in correspondence with the stress. 

 Hence the subsequent magnetizations produce no deflection 

 since the wire is without twist. Residual strain has been 

 wiped out. 



Figures 18-20 show that the residual strain when stress is 

 zero, increases with the preexisting stress, being greater at 



