1913-14.] The Hall and Transverse Thermomagnetic Effects. 209 
In the case of the Hall effect, the value of R is calculated for unit 
potential gradient instead of for unit current density, as it would seem that 
the coefficient calculated in this way should be more directly comparable 
with the coefficients S and Q. The value of R, therefore, is the transverse 
R 
s 
Q 
4- 
Warm 
- — 
Electric \ 
Current ^ 
Heat 
Current 
Heat x. 
Current 
— 
Cold 
+ 
Fig. 1. 
E.M.F. (electromagnetic units) in a plate of unit breadth when placed in 
unit magnetic field, the potential gradient along the axis being 1 electro- 
magnetic unit per cm. 
Apparatus. 
The specimen plate, abed (fig. 2), to be tested was soldered to two 
copper lugs L, L, which were themselves soldered to two brass tubes T, T. 
These tubes were fixed to a wooden frame, which served as a support. 
The breadth of the specimen plate was in all cases about 2 cm., and the 
distance between the lugs about 5 cm. The thickness differed for the 
different specimens, but was in all cases less than a millimetre. Wires 
were soldered to the brass tubes to enable an electric current to be sent 
through the plate for the Hall effect measurement. 
Five copper-constantan thermocouples were soldered to the plate at five 
points A, B, C, D, E. The three points E, B, and D were on the axis 
of the plate, while A and C were on a line perpendicular to this axis 
and passing through B. The distances between B and the other points 
were approximately 1 cm., but the actual distances were measured for 
each plate. 
The thermocouples were made of line wire (No. 42 S.W.G.), so as to 
avoid as far as possible any cooling effect due to conduction of heat along 
the wires. 
Two water jackets J, J, 8 cm. by 5 cm. and about 1 mm. thick, were 
placed one on each side of the plate, and were kept at a distance of 0*84 cm. 
apart by brass distance-pieces, thus forming a kind of box enclosing the 
specimen plate. The space between the plate and these jackets was filled 
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