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VIII. — The Electrical Resistance of Nickel at High Temperatures. By 

 Cargill G. Knott, D.Sc. (Edin.), F.RS.E., Professor of Physics, 

 Imperial University, Tokayo, Japan. (Plate XII.) 



(Read 5th July 1886.) 



In the Proceedings of the Royal Society of Edinburgh for 1874-75 there is a 

 short paper on the "Electrical Resistance of Iron at a High Temperature." 

 It is the record of certain experiments made by three of us, then students in 

 the Physical Laboratory of the University of Edinburgh ; and its conclusion is 

 that there is a peculiarity in the behaviour of iron as an electric conductor 

 at the temperature of a dull red heat. At this temperature other physical 

 peculiarities are known to exist, particularly as regards its thermal expansion, 

 its thermal capacity, and its specific heat for electricity. The discovery 

 of these striking properties we owe respectively to Dr Gore,* Professor 

 Barrett,! and Professor Tait.J 



Professor Tait's discovery, that the Thomson effect in iron changes sign at 

 certain high temperatures, is in itself very striking ; and, when taken in connec- 

 tion with other coexistent peculiarities, suggests various lines of inquiry. 

 The most obvious is, perhaps, the question as to its occurrence in other metals. 

 There is one other metal which rivals iron in thermoelectric eccentricity, namely, 

 nickel. At a temperature of 200° centigrade, its Thomson effect gradually 

 changes sign from a considerable negative value to a large positive value, 

 changing back again to nearly its original value at 300° C. If nickel thus 

 agrees with iron in one exceptional feature, it may well be expected to agree 

 in others. In short, Does nickel between the temperatures of 200° and 300° C. 

 undergo exceptional changes in length ? is there a phenomenon corresponding 

 to Barrett's reglow % and has the electric resistance any unusual change at 

 these temperatures ? The first and third questions may be readily answered 

 by experiment ; the second, however, seems to offer almost insuperable diffi- 

 culties as a subject of investigation. The following paper deals with the third 

 of these inquiries. 



I have thought it well to embody, along with the results for nickel, corre- 

 sponding results for iron. The chief reason for this is, that in the experiments 

 conducted in 1874 by Messrs Smith and Macfarlane and myself, only a 



* Proc. Roy. Soc. Edin., 1869, and Phil. Mag., 1869. 

 t Phil. Mag., 1873. 

 % Trans. Roy. Soc. Edin., 1872-73. 

 VOL. XXXIII. PART I. 2 C 



