304 Proceedings of Royal Society of Edinburgh. [sess. 
specimen of platinum wire and the other the cobalt strip that 
was the special object of investigation. The upper extremities 
of the rods were joined by stout copper strips to a commutator 
connected to a Wheatstone Bridge resistance-box of ordinary con- 
struction. 
In one series of experiments the lower ends of the rods with their 
connecting wires were dipped in a vessel of oil which could be 
heated up to a temperature of 240° C. A thermometer, centrally 
placed so that its bulb lay at the mean level of the platinum and 
cobalt coils, was used for measuring the temperature. The oil was 
heated very gradually and was kept briskly stirred until a few 
seconds before a reading was to be taken. One of the wires was 
meanwhile thrown into the Wheatstone Bridge, and the resistance 
adjusted slightly in advance. The temperature was then allowed 
to rise very slowly until reversal of the commutator in the galvano- 
meter branch gave no deflection. When the equilibrium was thus 
attained the thermometer reading was noted. In this experiment 
chief attention was given to the cobalt ; a few measurements of 
resistance were made with the platinum, sufficient to give the most 
important temperature coefficient. 
The resistance curves for the cobalt and the platinum are shown 
in the diagram, Nos. 1 and 2. All corrections have been carefully 
applied and the resistances are in legal ohms. 
By interpolation amongst a number of contiguous measure- 
ments, the resistances corresponding to the temperatures 100°, 
140°, 180°, and 220° C. were calculated. They are given in 
Table I., together with the measured resistance at the tempera- 
ture of the air. 
Table I .—Resistance of a Cobalt Strip in Legal Ohms at 
Different Temperatures. 
Temperature. 
Resistance. 
First Diff. 
Ratio. 
7°‘5 C. 
100 
140 
180 
220 
0-09604 
•12340 
•13694 
•15210 
T6859 
•01354 
•01516 
•01649 
' 
1T097 
1-1109 ! 
1-1084 i 
1 
