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XXIII. — Change of Electric Resistance of Nickel due to Magnetisation at Different 

 Temperatures. By Professor C. G. Knott, D.Se. 



(Read 16th June and 19th July 1902. Issued separately December 31, 1902.) 



Since Lord Kelvin showed that the resistance of the magnetic metals was influenced 

 by the state of magnetisation of these substances, a good deal of work has been done in 

 investigating more carefully the extent and nature of the relation. It does not appear, 

 however, that any attempt has been made to discover how change of temperature affects 

 this influence. Twelve years ago in Japan I set one of my Japanese students to the 

 construction of an apparatus suitable for making this research. A few preliminary 

 experiments were made ; and leaving Japan shortly after, I brought the apparatus with 

 me in the hope of continuing the work in this country. Not till this summer, however, 

 did I find leisure to return to the problem. The results obtained I wish now to lay 

 before the Society. 



The apparatus was constructed with a view to compensate as far as possible for the 

 inevitable changes of temperature accompanying the application of magnetising forces 

 by means of currents through coils. Two nickel wires of exactly the same length and 

 resistance were made into two similar flat coils which then serve as anchor ring cores 

 for the magnetising coils to be wound round. The magnetising coil round each 

 nickel was wound in two distinct portions with exactly the same number of turns. 

 When these two portions were joined together end to end so that the current flowed in 

 both in the same direction round the nickel core the nickel was of course magnetised. 

 But when they were connected so that the current in one flowed round the nickel in a 

 direction opposite to that in which the current flowed in the other, then the nickel was 

 subjected to no magnetising force at all. Thus by simply reversing the current in one 

 portion we could at once pass from strong magnetising force to none, and yet keep the 

 heating effect of the current practically unaltered. In the experiments, as conducted, 

 the two nickel wires formed neighbouring arms of a Wheatstone Bridge, and the same 

 current was passed round both, but generally in such a manner that only one was 

 magnetised. When the current was passed so as to magnetise neither, there was 

 observed no abrupt change of resistance at make and break of the current circulating in 

 the copper coils. This showed that the magnetic compensation when the two portions 

 of the coils acted in different directions was perfect. 



The nickel wires forming the cores of the anchor rings I shall distinguish by the 



letters M and N. Their ends were attached to the ends of stout nickel rods, three in 



all, one forming the junction where M and N met. These rods were lashed to a central 



brass pillar covered with asbestos cloth, so that all were carefully insulated one from 



TRANS. ROY. SOC. EDIN., VOL. XL. PART III. (NO. 23). 4 l 



