310 
Proceedings of Boy al Society of Edinburgh. [sess. 
The Thermoelectric Positions of Cobalt and Bismuth. 
By Professor Cargill G. Knott, D.Sc., E.R.S.E. 
(Read July 6, 1891.) 
So far as I know, the only satisfactory determination of the 
position of the cohalt line on the thermoelectric diagram was made 
by Professor Tait’s students in the Physical Laboratory of Edinburgh 
University some fifteen years ago. The position of the cohalt line, 
so found, was given along with the positions of certain alloys in a 
paper by Professor J. Gordon MacGregor and myself, published in 
the Transactions of the Royal Society of Edinburgh , vol. xxviii. 
(1878). The particular specimen of cobalt used in these early 
experiments was a short rod obtained by electrolytic decomposition. 
The noteworthy facts regarding its thermoelectric line were that it 
lay below nickel on the diagram, and that its inclination to the lead 
line was much greater than the inclinations of the iron and nickel 
lines. 
As a laboratory exercise, I gave to Mr Sawada, one of our students 
of physics, the task of studying the thermoelectric properties of the 
cobalt described in the preceding paper on electric resistance. The 
plan adopted was to form a multiple arc of palladium and bismuth, 
and, by proper adjustment of the resistances in these branches, to 
obtain an intermediate line which should cut through the cobalt line 
at temperatures within easy reach. 
Such an intermediate line passes through the neutral point of the 
component metals. It divides the region between their lines so that 
any transversal is cut into portions which are directly as the resist- 
ances in the branches of the multiple arc. Thus, by varying the 
ratio of the resistances in these branches, we may sweep through 
the region between the two corresponding diagram lines, interpolat- 
ing, so to speak, any intermediate line suitable for our purpose. 
The extreme accuracy with which we can measure electric resistance 
enables us to fix the position of this intermediate line as accurately 
as the positions of the component lines are known. 
In the present case, the low position of cobalt on the diagram 
very much circumscribed the choice of metals for the multiple arc. 
