984 
At 14°.5 K. the Harreffect is strictly proportional to the field, 
as is also the case at 20°.3 K..as far as H—9060. At 90° K: 
the Harrcoefficient is a linear function of the field, diminishing as 
the field increases. 
For the Harreoefficient in very weak fields the relation 
RK, =ce? 
holds. 
ne R 
The Lepuc quantity Dy = = the tangent of the angle of rotation 
of the equipotential lines in unit field, is here a linear function of 
the temperature. 
The following Table shows the extent to which those relations hold. 
f — Roobs, | Rocale. he Leate. | Props. 
290° K. || 66.0x 10-4 | 67.5x10-4|| 5.31 | 5.37 
9 | 41.2 10.5 | 3.07 | 3.10 
| |} | 
20.3 5.0 es Sapa 2250 
(14.5 5.1 | 5.0 fea | io apy 
For the nickel plate the magnetic change of resistance was also 
measured. / was 0.2 to 0.3 amp. 
As the resistance of the plate is very small, and the changes 
were, at the most, 1.5 °/,, it was not possible to evaluate them with 
any greater accuracy. 
As has also been observed by F. C. Brake *), G. Bartow?) and 
C. W. Herap*), there is an increase in the resistance of nickel in the 
weaker fields (H< 3000); in stronger fields the resistance diminishes, 
and, in the region 5600<H<10270, it does so approximately linearly 
with the field. This behaviour is, to a large extent, the same throughout 
the region 290° K. >7 > 14°.5 K. 
In strong fields the diminution in the resistance is somewhat greater 
at low temperatures than at ordinary temperature. 
1) F, CG. BLAKE. Ann. d. Phys. 28, 449, 1909. 
2) G. Bartow. Proc. Roy. Soc. 71, 30, 1903. 
5) CG. W. Heap. Phil. Mag. (6) 22, 900, 1911, 
