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XXIX. The Interactions of Circular and Longitudinal Mag- 

 netizations. {Preliminary Note.) By Prof. C. G. Knott, 

 D.Sc* 



IN the course of an extended series of investigations into 

 the relations of magnetism and stress, part of which is 

 already published in the Trans. Roy. Soc. Edinb. (vol. xxxv.), 

 I was led to consider the effect of a current passing along a 

 wire upon its longitudinal magnetic intensity. Wiedemann, 

 Buff, and Villarif have discussed this problem in some of its 

 aspects. It does not seem possible, however, to deduce from 

 their results completely satisfactory conclusions as to the 

 effect of the current upon the apparent longitudinal permea- 

 bility. The question as it presented itself to my mind was 

 not so much as to the effect of a varying current along the 

 wire upon the apparent longitudinal moment, but rather as to 

 the behaviour of the wire in various longitudinal fields 

 according as it was carrying a current or not. It was to be 

 expected, in accordance with the results of previous investi- 

 gators, that a diminution of longitudinal intensity would be 

 an evident accompaniment of a steadily sustained circular 

 magnetization. In other words, the susceptibility to a longi- 

 tudinal magnetizing force would, in all probability, be smaller 

 when a current was passing along the wire. This has been 

 fully established in the experiments, of which this forms a 

 short preliminary note. Other effects, however, have been 

 observed, which are (so far as I know) novel, and which may 

 lead to clearer views regarding the internal structure of 

 magnets and magnetized matter. 



In the experimental work I have been assisted by Mr. Tsuruta, 

 a graduating student of physics in the Imperial University. 



The wire to be experimented with was carefully annealed 

 and then inserted as the core of a solenoid of copper wire of 

 138 coils per centimetre length. The wire and solenoid lay 

 magnetically east and west, and at a suitable distance from 

 the one end a delicately suspended mirror with small magnets 

 attached to its back served in the usual way as the magneto- 

 meter. The deflexions were measured by the familiar reflected - 

 beam method, the spot of light moving over a scale at a dis- 

 tance of 1"7 metre from the magnetometer-mirror. Before 

 the w r ire was inserted, the electromagnetic action of the coil 

 on the magnetometer was corrected by a small adjustable coil 



* Communicated by the Author, having been read before the Royal 

 Society of Edinburgh, July 21, 1890. 



t For references, see Wiedemann's Die Lehre von der Elektrieitiit, 

 vol. iii. pp. 456-462 ; for theoretical discussion see p. 476. 



