306 Proceedings of Royal Society of Edinburgh. [sess. 
and by a rigorous process of interpolation, the cobalt resistances 
corresponding to assumed values of the platinum resistances were 
calculated. These are the numbers given in Table II., which 
epitomises the results of the four distinct experiments. The first 
column contains the platinum resistances, taken as convenient 
multiples of the resistance at 7° C., measured after the experiment. 
These virtually serve as a temperature scale. The other columns 
give in order the corresponding resistances of the cobalt, likewise 
all expressed in terms of the cobalt resistance at 7° C., measured 
after each experiment. 
Table II. 
Platinum 
Resistances. 
Cobalt Resistances. 
Experiment 
Experiment 
Experiment 
Experiment 
I. 
II. 
III. 
IV. 
2-0 
5-8047 
5-7996 
5-9748 
6-0361 
1-8 
4*5101 
4-3423 
4-4511 
4-4580 
1-6 
3-1822 
3-0536 
3-0932 
3*2216 
1*4 
2-2029 
2-1795 
2-1111 
2-2602 
1-2 
1 -5329 
1-5337 
1-5050 
1*0 
1-0000 
1-0000 
1-0000 
1-0000 
If we assume that the changes in the platinum resistance follow 
the same law as in the earlier experiment with the oil, the rise 
of temperature, which will just double the resistance, is about 
680° C. ; and the interval from 1 to 1*2 may be taken as 
corresponding to a rise of temperature of 136° C. According to 
the experiment in oil, this rise of temperature would have increased 
the resistance of the cobalt in the ratio 1*425 to unity. It is 
apparent then, that under the influence of the first excessive 
heating, the cobalt has been considerably altered in its properties, 
so that the average temperature coefficient for resistance up to 
150° C. has been increased by a quarter. The only other pos- 
sible explanation of this discrepancy is that the corrections to be 
applied for the resistances of the connections or contacts may 
have been underestimated in the second series of experiments, 
or overestimated in the first. There could, however, be no doubt 
as to the resistances of the connections, which were the same in 
