212 
Proceedings of the Eoyal Society of Edinburgh. [Sess. 
The copper wires belonging to the junctions at A and C were then 
connected to one of the galvanometer circuits, and the constantan wires 
of the E.M.F.’s in these two circuits were taken, first when the magnetic 
field was zero, and afterwards with magnetic fields of known strength in 
each direction. The thermoelectric force between copper and constantan 
at various temperatures being known from the results of a special 
experiment, the transverse temperature difference and the transverse 
potential difference due to the magnetic field could then be calculated, 
and hence the values of S and Q. 
Calculation of the Transverse Temperature Difference 
and Potential Difference. 
Before the magnet is excited there will be a certain difference of 
temperature between A and C. Let 0 be this difference, A being at 
a higher temperature than C. On account of this there will be an 
E.M.F., E, acting from A to C in the copper circuit, and an E.M.F., e, 
acting from A to C in the constantan circuit. If M and N are the 
thermoelectric powers of the metal of the plate with respect to copper 
and constantan respectively, there will be the relations : — 
When the magnetic field is excited, the temperature difference 0 is 
altered to some value 0 + SO, and at the same time a transverse potential 
difference is set up. Let this potential difference, measured from A to C, 
be denoted by V. 
Let the new values of E and e be E + <SE and e -f Se. 
There will be the relations : — 
from A and C to the other galvanometer circuit. Simultaneous readings 
E= -M0 
e= -N 0 
( 1 ) 
( 2 ) 
E + SE = V-M (6 + 8$) 
e + 8 e = Y_N (0 + S0) 
(3) 
(P 
Now, by subtraction of (4) from (3), 
(E - e) + (SE - Se) = (N - M)0 + (N - M )S0 
and from (1) and (2), 
E-e = (N-M )6; 
therefore 
SE-8e = (N-M)S0, 
or 
