608 ON ELECTRICAL RESISTANCE OF CERTAIN ALLOYS. 
platinum and iridium as the above, we found that “at low temperatures, the 
greater the percentage of iridium, the higher is the line on the diagram ;” but 
that “when we consider the position of the lines of other alloys of platinum 
and iridium determined by Tart, the above simple relation between the con- 
stitution of the alloy and the position on the diagram, does not seem to hold.” * 
It would thus appear that the thermo-electric properties of these alloys present 
peculiarities with reference to their chemical constitution similar to those of 
their electric conductivity. 
We have given above the formula showing the relation which holds between 
the conductivity and temperature of platinum. It is scarcely necessary to point 
out that for these alloys, as well as those we have considered above, the rate of 
variation of resistance is less than the rate of variation of the resistance of the 
chief constituent. As no observer has yet determined this rate for iridium, the 
conclusion on this point cannot be so general as in the case of the other alloys. 
For purposes of easy reference we give in Table LX. a synopsis of the above 
experiments. It contains the coefficients of the formule used above, which, 
stated generally, are: 
r=1+at—dt’, 
and 
k=1—at+ct’, 
as well as particulars as to the constitution of the alloys to which the coefficients 
refer. 
TABLE IX. 
Percentage Composition. 
Alloy. a. b. C. 
By Volume 
By Mass. (about) 
Tron-Gold, 5 of Fe. | 11-9 ‘of Fe. ‘00037198 00000038217 | :00000052054 
Platinum-Silver, 35 of Pt. | 21-1 of Pt. 00034802 ‘00000028066 | -00000040178 
Palladium-Silver, | 25 of Pd. | 23°6 of Pd. 00035764 00000011612 | :00000024403 
4 Se 20 of Pd. | 18°85 of Pd. ‘00043361 00000020665 | 00000039467 
Platinum-Ividium, | 6 of Ir. 6°57 of I. 0014526 00000157584 | -0000036859 
R +, 10 of Ir. | 10:92 of Ir. 0011766 ‘00000010855 | -0000014929 
is ‘. 15 of Ir. | 16:29 of i. ‘00078229 000000021063 | 00000063305 
7 e 20 of tr, |, 21-61 of Ir. 0010475 00000036832 | 0000014156 
The above experiments were performed in Prof. Tarr’s Laboratory, University 
of Edinburgh, nearly three years ago. Their publication has been delayed 
because of the lack of an opportunity of working up the results. 
Our thanks are due to Prof. Tarr, who furnished us both with the alloy wires 
themselves and the means of studying them. 
* See p. 335 of our paper cited above. 
