124 Proceedings of Royal Society of Edinburgh. [sess. 
On the Interaction of Longitudinal and Circular Magnet- 
isations in Iron and Nickel Wires. (Second Note.) By 
Professor Cargill G. Knott. 
(Read February 16, 1891.) 
In a preliminary note communicated last July,* I drew attention 
to what seemed a novel property of iron wire under the combined 
influence of circular and longitudinal magnetisations. Similar ex- 
periments were subsequently tried with nickel, and similar results 
obtained. It appeared, however, that in some respects nickel behaved 
oppositely to iron. The first series of observations brought out the 
fact that a current along the nickel wire seemed to assist the ac- 
quiring, under a longitudinal magnetising force, of a polarity 
oppositely directed to the direction of the current. 
Unfortunately the necessity of stopping work during the hot 
summer months postponed the discovery that much if not all of the 
supposed curious effect in iron and nickel was due to the existence 
of a twist in the wire. It should he mentioned that the wires were 
set up with great care, being first annealed, then brazed to terminal 
pieces, then annealed a second time under horizontal tension sufficient 
to keep them straight in a direction perpendicular to the magnetic 
meridian. To one of the terminals two copper wires, laid parallel 
to and on each side of the nickel or iron wire, were soldered ; and 
the set of three wires was placed in position in suitably arranged 
grooves cut along the plane surface of a semi-cylinder of wood. The 
other half of the cylinder was then superposed so as to keep the 
wires firmly in position ; and the whole arrangement was lifted 
from the place where the final annealing had been accomplished 
and inserted into its position in the heart of the magnetising coil. 
Exactly when the wire got twisted it is impossible to say. It must 
have been a small twist ; but that it did acquire a permanent twist 
is sufficiently proved by later experiments in the months of October 
and November 1890. 
In these later experiments a slightly different arrangement was 
adopted. The wire to be treated, after careful annealing, was 
* See also Phil. Mag. for September 1890. 
