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XIX. — Magnetization and Resistance of Nickel Wire at High Temperatures. 

 Part II. By Professor 0. G. Knott, D.Sc. 



(Read December 17, 1906. MS. received same date. Issued separately April 1, 1907.) 



The experiments which form the subject of the present communication were carried 

 out two years ago, and supplement results already published.* A brief note of some of 

 the results was read before the Society in June 1904, and was also read before the 

 British Association Meeting at Cambridge in August of the same year. 



The previous paper discussed the effect of high temperature on the relation between 

 electrical resistance and magnetization when the wire was magnetized longitudinally, 

 that is, in the direction in which the resistance was measured. 



The present results have to do with the effect of high temperature on the relation 

 between resistance and magnetization when the magnetization was transverse to the 

 direction along which the resistance was measured. 



Since the publication of my note in 1904, an interesting paper by W. E. Williams, 

 B.Sc, on the same subject, has appeared in the Philosophical Magazine for January 

 1905. His work has to do chiefly with resistance change in the direction of magnetiza- 

 tion, and covers a good deal of the ground I had mapped out for my own investigation, 

 so that it is no longer necessary for me to pursue that line of inquiry. Mr Williams 

 was able to work up to much higher fields than I was able to obtain with my form of 

 apparatus, and one novel result obtained by him was the reversal of the sign of the 

 resistance change in high transverse fields at ordinary temperatures. He does not 

 seem, however, to have studied the effect of transverse fields at high temperatures. 

 Some of his results in the high-temperature experiments in longitudinal fields have a 

 resemblance to the curious effect communicated in my note of 1904. This peculiarity 

 I now desire to give in detail. 



As mentioned in the former paper, my first attempts to measure the change of 

 resistance of nickel wires due to transverse magnetization were unsuccessful, simply 

 because of the thinness of the wire in the direction of the magnetizing force, and 

 because the fields attainable were too small. By inserting a flat coil of nickel wire in 

 the short air-gap of an electromagnet, I was able to obtain measurable changes. The 

 wire was carefully wound in a flat coil between two mica strips, the contiguous parts of 

 the coil being kept apart by asbestos thread coiled in between, t The coil was enclosed 



* " Magnetization and Kesistance of Nickel Wire at High Temperatures," Trans. Roy. Soc. Edin., vol. xli. 

 pp. 39-52, 1904. 



t It is of great importance to make sure that, when the flat nickel coil is magnetized, the lines of force are 

 directly transverse. A slight component of field along the wire brings in the longitudinal effect which may, under 

 certain conditions, affect the sign of the change of resistance, especially in low fields. It was only after several trials 

 that a satisfactory flat coil was obtained. 



TRANS. ROY. SOC. EDIN., VOL. XLV. PART III. (NO. 19). 77 



