THE ELECTRICAL RESISTANCE OF CERTAIN ALLOYS. 605 
These measurements may be condensed in the following formula : 
R= 201797 + :000875¢— 0000004177, 
whence 
‘ r=1+°00043361¢— 000000206657’, 
an 
k=1—-00043361¢ + 000000394677’. 
It will be noticed that the resistances corresponding to the lowest three 
temperatures and calculated by the formula do not agree well with those ob- 
served. They are all somewhat less. If the temperature and resistance 
measurements be plotted so as to give a curve, it will be found to be very 
nearly a straight line at the lower temperatures. From about 70° C. down- 
wards the rate of change of resistance is sensibly constant. We have thought 
it better, however, to use a formula of the same form as we have used for the 
other alloys, than to seek slightly greater accuracy in a new form. 
MArruHiessEN and Vocrt have studied no alloy whose composition is nearer 
this one’s than that to which we have already referred. 
The coefficient of ¢is in this case also less than the coefficient of ¢in the 
formula of either of the constituent metals. 
Platinum-Inidium Alloys. 
We have examined four platinum-iridium alloys. Table V. gives the ob- 
servations on one containing 6 per cent. by mass, or about 6°57 per cent. 
by volume of iridium. 
TABLE V. 
Resistance. 
Temperature. 
Observed. Calculated. 
16:07 C. 14945 14°876 
40:0 15:351 15°351 
61:8 IPs eye 15°761 
80:5 16:095 16:095 
100°5 16:465 16°435 
119°8 16°75 16°745 
155-2 17:245 17-270 
From these numbers we deduce the formula, 
R=14'543 + :021125¢—-00002291772?, 
whence 
r=1+:'0014526¢ — :000001575842?, 
and 
k=1—'00145262 + 000003685927, 
