601 
of Edinburgh, Session 1871 - 72 . 
The two oblique straight lines in the diagram belong to the metals 
a, b , respectively. The tangents of their inclination to the horizontal 
axis (the line of the supposed metal for which k = 0) are h a , k b —and 
they cut it at the points T a , T d , where they are neutral to it; cut¬ 
ting one another at a point A whose abscissa is their own neutral 
point T ab . The only change which would be introduced, by taking 
as horizontal axis the line corresponding to a metal for which k 
does not vanish, would be a dislocation of the diagram, by a 
simple shear. This follows at once from the equation of one of 
the lines— 
y = h a (x- T„). 
The diagram gives the Peltier effect at the junction of a and b 
for any temperature t v by drawing the ordinate at t v and completing 
a rectangle cc'gf' on the part intercepted, its opposite end being at 
absolute zero. The area of this rectangle is to be taken positively 
or negatively according as the corner corresponding to a is nearer 
to, or further from, the horizontal axis than that corresponding 
to b , the current being supposed to pass from a to b. 
The electro-motive force in a circuit of the two metals, a and b , 
with its junctions at t x and t 2 respectively, is found by drawing 
ordinates at these temperatures, so as to cut off triangular spaces 
Acc', Add', whose vertices are at the neutral point. The difference 
