72 Mr. W. C. Baker on the Hall Effect in 



but above J5=t00 the rate becomes less and the contraction 

 reaches a maximum in ^==900, whence to return gradually 

 with further increase of the field. 



[b) Annealed cobalt contracts at a steady rate as the 

 field is increased. The contraction becomes ultimately greater 

 than in cast cobalt. 



3. The increase of volume in 46 per cent. Ni, 36 per cent. 

 Ni, 29 per cent. Ni steels takes place almost in proportion to 

 the strength of the field. The amount of the increase becomes 

 greater as the percentage of nickel becomes less. The volume 

 change in 29 per cent. Ni is the greatest that has ever been 

 observed, and is nearly 40 times that in iron, in strong fields. 



Wiedemann Effect. 



The twist produced by the combined action of circular and 

 longitudinal magnetization in iron, nickel, and nickel-steel 

 increases with the longitudinal field-strength, and reaches a 

 maximum whence it decreases gradually as the field is further 

 increased. The sense of twist in iron and nickel-steel is 

 opposite to that in nickel. The transient current produced 

 by twisting a longitudinally magnetized wire and the 

 longitudinal magnetization caused by twisting a circularly 

 magnetized wire are reciprocally related to the twist 

 produced by longitudinal and circular magnetizations. 



Physical Laboratory, Imperial University, 

 Tokyo, March 1902. 



V. On the Hall Effect in Gold for Weak Magnetic Fields. 

 By Will. C. Baker, M.A., 1851 Exhibition Scholar from 

 Queen* s University, Kingston, Ontario , Canada, JVon- Col- 

 legiate Student, Cambridge *. 



VON ETTINGSHAUSEN and Nernstj found that the 

 Hall coefficient in certain bismuth-tin alloys depended 

 on the strength of the magnetic field employed. This change 

 extending, in some cases, even to a reversal of the sign of 

 the effect. Kundtf, in his work on the Hall effect in iron, 

 cobalt, and nickel, showed incidentally that the coefficients for 

 gold and silver remained constant even to fields of 21500 

 C.G.s. units. 



In view of the above, Professor J. J. Thomson suggested 

 that it would be of interest to examine the behaviour of pure 



* Communicated by Prof. J. J. Thomson. 

 i Wied. Ann. xxxiii. p. 474 (1886). 

 j 2«xlix. p. 21x4(1893). 



