83 
of Edinburgh, Session 1875 - 76 . 
specific gravity produced by the rolling up of the wires, their 
extension by weight between the first determination of specific 
gravity and the first determination of resistance, the irregularity in 
their cross section produced by stretching, and the slight contrac- 
tion of the wires after the removal of the weights and before the 
second determination of specific gravity,— all of which, however, 
must have been exceedingly slight. It seems to warrant the state- 
ment that if tension has any effect upon silver wires at all the effect 
is exceedingly small. This differs from Mousson’s conclusion as 
to steel, iron, and copper wires. He found that the increase in 
their resistance produced by stretching was not fully accounted for 
by the change of their dimensions. 
In the course of the experiments I found that by raising a silver 
wire, which had been stretched, to a red heat, its resistance was 
very slightly diminished. A wire of about the dimensions of No. 
III., which, after having been stretched by 6985 grms. had a re- 
sistance of 1-8135, had, after being heated red hot, a resistance of 
1-8103. This is again different from what Mousson has found to 
be true of steel, iron, and copper wires, but it agrees with a deter- 
mination made by Becquerel on silver wires.* 
The following tables contain series of observations made for the 
purpose of finding the relation between the stretching weight and 
the total increase in the resistance of the silver wires used. In 
these determinations, the constant resistance with which the resist- 
ances of the stretched wires were compared was that of a silver 
wire. Both wires were surrounded by a coating of steam. The 
stretched wire, in order that, by its being kept at a high tempera- 
ture, greater elongations might be produced by the same weights ; 
the constant wire in order that thermo-electric effects might be 
eliminated. The steam coating was formed by enclosing the wires 
in glass tubes, and these tubes in a much larger tube, and conduct- 
ing steam between them. In other respects the apparatus and 
mode of procedure were quite the same as before. The observa- 
tions were made when the appended weights had ceased to produce 
any appreciable elongation, and with the steam coating half-an- 
hour was generally found to be a sufficient length of time for the 
production of the total stretching effect. 
* “ Ann. de Chimie et de Physique” (3), xvii. 1846, p. 253. 
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VOL. IX. 
