AND RESISTANCE OF NICKEL WIRE AT HIGH TEMPERATURES. 551 



covery, there is a marked change in the Thomson Effect in nickel about these tempera- 

 tures, and it is conceivable that peculiarities may be detected in the same region if 

 definite search is made for them. 



Accordingly I asked Miss Eveline MacLaren, a student working in the Physical 

 Laboratory, to make a search for such a peculiarity. To this end a fairly long nickel 

 wire was coiled seven times on itself and made the core of an anchor ring coil. Four 

 separate coils were wound round it : two for magnetizing purposes, one for heating to 

 various temperatures, and one for measuring the induction ballistically. The heating 

 coil was wound anti-inductively, and all the wires were insulated with asbestos. The 

 temperature of the nickel wire in any experiment was measured by the resistance of the 

 wire. The investigation was carried out only between the limits of temperature already 

 indicated ; for there was nothing to be gained by repeating experiments which have 

 already been done on the relation of permeability and temperature. I give the results 

 at the end, although no peculiarity of the kind looked for was observed. It should be 

 noted, however, that in these experiments we are dealing with comparatively weak 

 longitudinal fields, and not with fairly strong transverse fields. 



The lowest temperatures used in these experiments are just low enough to show the 

 maximum reached by the induction in given fields as the temperature rises from about 

 200° to 240° C. The induction and permeability fall off very rapidly as the tempera- 

 ture of 320° C. is approached, and there is a suggestion that the temperature at which 

 magnetic permeability becomes unity depends to some extent upon the magnetizing 

 force applied. There is, however, no hint of anything peculiar corresponding to the 

 effect described above. 



As noted above, Mr Williams obtained, in high longitudinal fields at high tempera- 

 tures, a result somewhat resembling the effect discussed in this paper, At the higher 

 temperatures the curves showing the relation between longitudinal field and resistance 

 increase had each a distinct maximum, dipping down towards the axis in the higher 

 fields. At temperature 328° the curve cut the axis at field 630, so that the resistance 

 change became decrease in higher fields. At temperatures 334° and 345° the curves 

 cut the axis at fields 230 and 120 respectively, and the resistance decrease attained 

 considerable values in the highest fields. At temperature 355°, however, the curve lay 

 wholly below the axis, but very close to it throughout the whole range of magnetizing 

 force. When the results are shown by means of curves for constant fields, giving the 

 relation between resistance change and temperature, we find that in field 50 the change 

 of resistance is always increase and falls off to very small values as temperature 350° is 

 approached. On the other hand, in field 800 the resistance change is increase up to 

 temperature 326°, becomes decrease for higher temperatures, passing through a 

 minimum (maximum decrease) about temperature 340°, and thereafter diminishing 

 numerically to very small values as 370° is approached. 



That is to say, the change of resistance due to the application of certain longitudinal 

 fields passed through a minimum value before finally vanishing at the highest tempera- 



