1890-91.] Prof. C. G. Knott on Electric Resistance of Cobalt. 308 
The Electric Resistance of Cobalt at High Tempera- 
tures. By Professor Cargill G. Knott, D.Sc., F.R.S.E. 
(With a Diagram.) 
(Read July 6, 1891.) 
The manner in which the electric resistance of cobalt varies with 
high temperatures does not seem to have been studied with any 
great care. The peculiar behaviour of iron and nickel as regards 
their change of resistance with temperature is now well known.* 
With a view to discover if cobalt presented any similar peculiarity, 
I set Mr Omori, one of the physical students in the Imperial Uni- 
versity, Japan, to investigate the question. The chief results are 
embodied in the present short paper. 
The piece of cobalt used was cut from a sheet of rolled cobalt 
which had been given me by Professor Tait. Dr E. Divers, E.R.S., 
very kindly determined its composition by analysis of a small 
quantity (about 20 grains) supplied to him. The result of the 
analysis is as follows : — 
Carbon found, . . . . 0*77 per cent. 
Silicon, . . . . . 0T5 „ 
Iron, ..... 0*73 „ 
with a minute quantity of manganese and perhaps y 1 ^ per cent, of a 
metal undetermined. The carbon might be as much as 1 per cent. 
Dr Divers regarded the cobalt as of remarkable purity for a furnace 
product. 
The experiments now to be described were carried out in January 
and February of 1890. The method was essentially the same as 
that used in my earlier investigations on nickel. Four stout copper 
rods, 60 cm. long, 0'7 square cm. cross-section, were fixed in a 
vertical position some little distance apart. Their lower extremities 
were joined in pairs by two coiled wires, one of which was a 
* See my paper “On the Electric Resistance of Nickel at High Tempera- 
tures,” Trans. Roy. Soc. Edin., vol. xxxiii., 1886. 
