1913-14.] The Hall and Transverse Thermomagnetic Effects. 221 
the plate, and this will have an effect on the value of Q. In consequence 
of this, it is not to be expected that the ratio ^ will be so nearly 
constant as | 
On examining the experimental results, it will be seen that there is 
no simple relation between the temperature coefficient of Q and those of 
R and S. This is easily accounted for by the fact, previously pointed out, 
that the potential effect is influenced by causes other than those which 
determine the other two effects. On the other hand, some relation is to 
be expected between the temperature coefficients of R and S. 
On the assumption that only negative carriers need be considered, 
the electron theory leads to the expressions 
R = A 
eXu 
S = B 
eXu 
I^T 
j 
where e = the electronic charge 
A = mean free path, 
u= ^/njean square velocity of electrons, 
«T = K.E. of electron at absolute temperature T due to its linear 
motion. 
A and B are factors depending upon the distribution of the magnetic 
field within the metal. 
Now, if R and S are influenced in the same way by the distribution 
R 
of the magnetic field, the value of is unity, and should be independent 
o 
both of field strength and temperature. There is a rough approximation 
to this in the case of copper and zinc. In the case of iron the value of 
R 
g-, although considerably greater than unity, does not vary greatly with 
variation of either field strength or temperature. 
In the case of nickel, however, a very considerable discrepancy is 
apparent. It is difficult to account for this discrepancy except on the 
assumption that the values of R and S do not depend in quite the same 
way upon the distribution of the magnetic field. This is not inconceivable, 
since in the case of the heat current the electrons are moving with 
velocities which remain constant between two collisions, whereas in the 
case of the electric current the velocities of the electrons are subject to an 
acceleration. 
The galvanomagnetic temperature effect, which has not been considered 
in this paper owing to the difficulty experienced in measuring it in such 
