1902.] on the Electric Conductivity of Iron and Nickel. 39 



place in the highest fields, a peculiarity that could not be accounted 

 for by the experimental errors. In order to investigate this effect in 

 still higher fields, the following experiment was made :— 



Experiment II. — longitudinal Effect in Nickel. 



The method used was the same as in Experiment I, but the apparatus 

 was simplified and made as small as possible. The nickel wire was 

 wound on a glass cylinder as before, the number of complete turns 

 being thirty-four and length of cylinder only 5 mm. A small ballistic 

 coil was placed in the axis of the nickel coil in order to determine the 

 field. Finer pole pieces were used and the distance between them 

 reduced to 7*5 mm. No attempt was made to measure the magnetisa- 

 tion, and the field determined by the ballistic coil is assumed to be 

 the same as that in the nickel : as this had been proved to be approxi- 

 mately true in the former experiment. 



Results. — The change of resistance now exhibits a decided maximum — 



Ac£ = 0-0156, H = 2000 c.g.s., 



and in higher fields decreases continuously to the value 



= 0-0100, H = 18,000 c.g.s. 



To explain this result it appears necessary to consider the effect of 

 the end-elements of the nickel coil. In this apparatus the end-elements 

 formed a considerable fraction of the whole coil, whereas in Experi- 

 ment I this fraction was small. These elements of the wire are 

 magnetised transversely. Even if there were no transverse effect in 

 nickel, the existence of the end elements reduces the observed change 

 of resistance, and the necessary correction cannot be estimated. But 

 the electrical resistance of nickel is diminished by the transverse mag- 

 netisation, and this effect may therefore easily explain the peculiar 

 results of the above experiment. 



Experiment III. — Transverse Effect in Nickel. 



The above experiments suggested that an examination of the 

 transverse effect in the same specimen of nickel would prove of con- 

 siderable interest. For this purpose a coil of the nickel wire was 

 wound non-inductively on a short brass bobbin provided with wide 

 flanges. The plane of the coil was placed at right angles to the lines 

 of force, so that the whole of the wire was magnetised transversely. 

 Very strong fields were obtainable on account of the small thickness 

 of the coil, 3 mm. only. It is impossible to measure the magnetic 

 field which exists in the metal in such a case, but the field undis- 

 turbed by the nickel coil was determined for each measurement of the 



