1890-91.] Prof. Knott on Interaction of Magnetisations. 127 
length of 48 centimetres, or 12 J minutes per centimetre length. 
The results' obtained were as follows for this and other twists, all 
indicated in the first column : — 
Twist. 
Current. 
Field. 
Range. 
Polarity. 
+ 12'-5 
0 
± 
343 
+ 1-5 
+ 2-1 
195 
+ 12*5 
-2T 
3 3 
187 
-18-5 
+ 25' 
0 
3 3 
350 
-5 
+ 21 
195 
+ 17-5 
-21 
33 
193 
-24-5 
+ 37 *'5 
0 
> ) 
338 
-6 
+ 21 
3 3 
168 
+ 39 
-21 
3 3 
167 
-43-5 
+ 12' -5 
0 
3 3 
355 
+ 0*5 
+ 21 
202 
-4 
-21 
3 5 
202 
-1 
0 
+ 21 
207 
-1-5 
-21 
33 
211 
-3-5 
-37-5 
0 
3 3 
357 
+ 1-5 
+ 21 
3 3 
205 
-10-5 
-21 
3 3 
206 
+ 5 
In Part II. of my paper on certain relations between magnetism 
and twist on twisted iron and nickel wires,* I have worked out in 
detail the changes of longitudinal polarity produced by twisting a 
wire when a current is passing along it, or by reversing the current 
along it when the wire is twisted. In the latter case, if the wire is 
twisted right-handedly (so that any line in it originally parallel to 
the axis becomes a right-handed screw), the longitudinal intensity 
is co-directional with the current in iron, anti-directional in nickel 
—a fact first established by Wiedemann. In the light of this fact, 
the experiments just described become intelligible. The sign of 
the polarity acquired is to a large extent determined by the twist in 
the wire. In the fourth series, in which the wire was untwisted 
* Not yet published. See, however, a short paper on “ Magnetic Priming 
and Lagging in Twisted Iron and Nickel Wires,” Journal of the College of 
Science, Imperial University, Japan, vol. iii. (1889) — Abstract in Wiede- 
mann’s Beiblatter, vol. xiii. 
