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IlIl.—Magnetization and Resistance of Nickel Wire at High Temperatures. 
By Professor C. G. Knott, D.Sc. 
(Read May 4, 1903. Given in for publication November 12, 1903. Issued separately March 3, 1904.) 
In a recent paper published in these Transactions* I gave an account of certain 
experiments upon the change of electric resistance of nickel due to magnetization at 
different temperatures up to 100° C. In the closing sentence of that paper I pointed 
out the advisability of trying to push the temperature up to 400° C., the temperature 
at which nickel loses its pronounced magnetic properties. This has been accomplished 
in the experiments now to be described. These refer, meanwhile, to the effect of 
longitudinal magnetization on the resistance of the wire. The experiments on the 
effect of transverse magnetization are still incomplete, and are reserved for a 
future communication. 
1. THE APPARATUS USED.—Since the temperature was to be raised to about 400° C., 
it was necessary to use asbestos for insulation. Accordingly, two exactly similar anchor- 
ring coils with nickel-wire cores were constructed. ‘These coils were about 18°3 cm. in 
diameter. Round the flat circular coil of nickel which formed the nucleus of the 
anchor-ring two independent layers of copper wire, carefully insulated throughout, were 
coiled, with the same number of turns in each. The ends of the two copper-wire coils 
could be joined in different ways, so that it was possible to have a strong current pass- 
ing through both, and yet to have, at will, either strong magnetization within or none 
at all. The magnetizing force could thus be removed at a moment’s notice by simply 
reversing the current through one of the coils of copper wire, while the heating effect 
of the current on the whole coil could be maintained unaltered. To preserve as con- 
stant a temperature as possible during any one set of observations was of the highest 
importance, for the change of resistance due to a very slight change of temperature was 
sufficient to mask completely the change due to magnetization. This change was 
measured by means of a Wheatstone Bridge arrangement. The galvanometer was made 
of a convenient sensitiveness for the purpose; and only when a very steady tempera- 
ture was obtained during a set of observations was the galvanometer in a steady 
enough state of approximate balance to render measurements possible. It was for the 
purpose of further reducing the disturbances due to changing temperature that two 
anchor-ring coils were used, with equal lengths of nickel wire as the cores, and with 
the same magnetizing or merely heating current flowing through both double coils of 
copper wire. 
* Vol. xl. pp. 5385-545. 
TRANS, ROY. SOC. EDIN., VOL, XLI. PART I. (NO. 3). 7 
