6o 
PHYSICS: C. BARUS 
Proc. N. a. S. 
20 amperes, I observed no temporary effect in excess of the quiver of the 
fringes. 
a 
— 
■i 
— >■ 
FIG. 1 
The following data were obtained for the fringe displacement AA/", 
showing the permanent effect of reversal of current: 
Current, 3 Am. 
10 Am. 
20 Am. 
AiV = ? 
0.00031 cm. 
0.00065 cm. 
Below 3 amperes I was unable to observe a displacement. For larger 
currents the twist increases proportionally to the current passing the tube. 
It is probable that here, as in similar cases in magnetization, fields below 
a certain small value are ineffective, as though there were static friction. 
A further observation is to be made: If a certain magnetic set is 
produced by a stronger current (say, 20 amperes), then a weaker current 
(say, 10 amperes) is unable to modify it, provided both currents are in the 
same direction. If this weaker current is reversed, the change of twist 
