1890-91.] Prof. Knott on Interaction of Magnetisations. 129 
polarity was in this case obtained at the first putting on of the 
current. The necessary fingering of the wire when clamping its 
ends seemed to give a slight twist, sufficient, however, to produce 
the effect spoken of. We may suppose the existence of the effect 
to prove that a twist did originally exist in the wire. I shall call 
for convenience this unknown initial twist x'. The results are 
these : — 
For Nickel Wire of Diameter 09 mm. 
Twist. 
Current. 
Field. 
Range. 
Polarity. 
x' 
0 
± 
273 
+ 20*5 
+ 2*43 
3 3 
240 
+ 113 
-2*43 
3 3 
238 
- 46*5 
£c' + 12'*5 
0 
3 3 
287 
+ 29*5 
+ 2*43 
237 
- 66*5 
-2*43 
3 3 
239 
+ 102*5 
In the first series (for twist x'), the range of polarity due to the 
reversal of the current was only 10, whereas the difference of the 
average polarities associated with positive and negative currents is 
as much as 159*5. It will he noticed that in passing from twist x' 
to twist x' + 10', the sign of the difference of polarities changes 
from positive to negative ; while the amounts of the differences are 
nearly the same. This would indicate that x ' had a value of approxi- 
mately - 5 ' ; so that a?' +10 becomes +5'. I am by no means 
satisfied, however, that (in nickel wire at any rate) there does not 
exist a measurable difference of polarities due to the current only. 
The great difficulty is to be sure that no twist exists in the wire ; 
for it is quite evident that a very small twist is sufficient to produce 
a very large average polarity, when the wire is subjected to a steady 
circularly magnetising force in conjunction with a cyclically vary- 
ing longitudinal field. If the effect is due only to the twist in the 
wire, we have here an extremely sensitive process for demonstrating 
the existence of a twist, especially in nickel wire. 
The whole subject calls for more detailed discussion ; and I am 
impelled to communicate these earlier results chiefly with the desire 
of correcting any false impressions that my preliminary note of last 
July might very easily give rise to. The facts there described are 
vol. xviii. 30/4/91 i 
