ON STANDARDS OF ELECTRICAL RESISTANCE. 149 
that care was taken to have the alloy drawn by different persons, in order to 
see if this would influence the results obtained with them, as well as to ascer- 
tain whether the wires would show the same faults as silver and copper does 
when not carefully drawn. It has been argued that the molecular condition 
of all alloys is liable to undergo a change by age, and that, therefore, alloys 
are not fit to be used as standards. Thus, it is well known that brass and 
German silver become brittle and crystalline by age, and that the same may 
eccur with the gold-silver alloy; but on looking at the composition of the 
alloy, it will be found to have nearly the same as that of the gold chains of 
commerce. Now, we do not know of a single instance where such a 
chain, even after years of use, becomes brittle or crystalline; so that we 
think it more than possible that the alloy will not change its molecular 
condition by age. It must also be remembered that even when German sil- 
ver becomes brittle, it does not materially alter in its conducting power. The 
same has already been proved, and mentioned in this Report, to be the case 
with iron and cadmium. 
3. On the effect of annealing on the conducting power of the alloy—When 
the alloy is heated to redness and cooled slowly, its conducting power was 
found to have increased only 0-3 per cent.—this value being the mean of 
eight wires annealed in different ways,—proving, therefore, that if the wires 
may be only partially hard-drawn, it will make but little difference in the 
conducting power. 
4. On the influence of temperature on the conducting power of the alloy — 
When wires of this alloy are heated from 0° to 100°, a decrement in the con- 
ducting power, amounting to 6-5 per cent., will be found. The same argu- 
ments may, therefore, be put forward in favour of the use of the alloy asa 
standard, as were done in the case of mercury when speaking of this pro- 
perty. 
To sum up, therefore, the arguments in favour of and against the use of 
the three propositions made to reproduce standards of electric resistance, we 
find in favour of a pure metal in a solid state :— 
1. That it appears that all descriptions of electrotype copper, when carefully 
drawn, have the same conducting power. 
Against it :— 
1. That their preparation, with the exception of the electrotype copper in 
a state of purity, is exceedingly difficult ; so that independent persons pre- 
paring the same metal find, on comparing the conducting powers obtained 
for them, that they vary several per cent. 
2. That the influence of annealing on their conducting powers is so great 
that differences may occur simply because the wires are partially hard-drawn. 
3. That the influence of temperature on their conducting power is very 
great; so that slight errors in thermometers, or in the reading of them off, 
would materially affect the result. 
In favour of using mercury as a means of reproducing standards the fol- 
lowing may be said :— 
1. That no molecular change can take place in the metal, nor can any 
alteration occur in its conducting power, on account of annealing ; for its tem- 
per is always the same. 
2. That the influence of temperature has only a small effect upon its con- 
ducting power. 
And against it :— 
1, That there is a difficulty in obtaining absolutely pure mercury ; 80 that 
the results obtained by different observers show great variations. 
