114) On an Alloy to be used as a Standard of Electrical Resistance. 
Taking the conducting power at 0°=100, we have 
for (a), X=100—0:06714¢ + 0:0000218 7?, 
(6), N=100—0:06753 ¢ + 0-:0000274 2?, 
mean A=100—0:06734¢ + 0:0000246 2, 
which shows there is a difference in the conducting powers at 
different temperatures between annealed and hard-drawn wires 
of this alloy. 
A similar difference we have already found between hard- 
drawn and annealed silver wires. 
Although the values found for x and y do not agree very well 
with each other, yet for all purposes it will not make much dif- 
ference which is used, as they will lead to the same results ; 
thus, if we calculate the conducting power for the highest ordi- 
nary summer temperature (in a room), say 30°C, we find it in 
the one case to be 
98:005, and in the other 97-999. 
In Table IX., I have given the differences in the conducting 
powers of some metals between O° and 100°, taking the con- 
ducting power at 0°=100. 
Table IX. 
Silver iahs sshageaeeeasinde 28°5 per cent. (annealed). 
GOpper «osc 0pendejsenasseani 29°0 per cent. (annealed). 
GOld: cn iesapsnayenacnssesss 28°0 per cent. (annealed). 
MBrCar ysis ins cccsesvanpes sss 8°7 per cent. (Siemens). 
The gold-silver alloy...... 6°5 per cent. (hard-drawn). 
6°7 per cent. (annealed). 
From the foregoing Table it will be seen how well the alloy is 
adapted for use as a standard to compare the resistances of 
other metals. . 
Whilst making these experiments, I have found that as soon 
asmost of the pure metals are alloyed with traces of any other, 
these differences rapidly decrease, in fact, almost in the same 
proportion as the conducting power of the metals themselves. This 
may explain why the copies of Weber’s standard vary so much 
one from another. For imstance, I have tested a commercial 
copper wire whose conducting power only varied between O° and 
100° 7 per cent (about), whilst pure copper varies 29 per cent. 
Now, suppose a wire of that copper whose conducting power 
only varies 7 per cent. between O° and 100° be compsred with 
one of Weber’s standards at a certain temperature, and then with 
a pure copper wire at another temperature, say 20° difference, it 
is obvious that the pure copper wire will not have the same re- 
sistance as the original standard. It has as yet been generally 
assumed that the conducting power of all copper wire, whether 
