i 10 MR. H. TOMLINSON ON THE INFLUENCE OF STRESS 
Expei 'imei 1 1 XXXIX. 
A piece of annealed piano-steel wire, S feet in length and '083 centirn. in diameter, 
cooled suddenly by plunging it into cold water after it had been heated to various 
temperatures. 
Condition. 
Number proportional to 
specific resistance.* 
Soft. 
•91168 
Heated and cooled, hiss not audible. 
•91095 
Heated and cooled, hiss just audible. 
■91094 
Heated below dull red but hiss very audible on cooling . 
•91118 
Heated to dull red and cooled. 
•91891 
In this last experiment the wire was tempered when coiled, the coils being held 
together by wrapping fine iron wire round them, and passing a burner rapidly round 
the coils until it was supposed that the requisite temperature had been applied, when 
the wire was suddenly plunged into water at a temperature of 10° 0. 
This experiment, though rough as regards the mode of tempering, shows plainly that 
the specific resistance is decreased by the sudden cooling until the tempering is per¬ 
formed at some temperature under dull red, when the specific resistance begins to 
increase. It will be shown also in Part TV. that the thermo-electric properties of steel 
are affected in precisely the same manner, that is, that tempering beyond a dull red 
temperature produces opposite effects to tempering under a dull red temperature. 
The Recovery of Electrical Conductivity produced by Time in Wires 
WHTCH ARE IN A STATE OF STRAIN. 
In all the experiments described in this Part it was observed that when the wires had 
been subjected to stresses of any kind, whether purely mechanical or otherwise, which 
sufficed to produce permanent strain, they invariably gained in electrical conductivity 
when allowed to rest. The amount of decrease of resistance produced by rest varied 
however considerably with different, metals, being very conspicuous in German-silver 
and hardly perceptible with platinum-silver. 
Table XIX. shows the influence of rest in restoring the electrical conductivity of 
wires of German-silver, copper, iron, zinc and platinum-silver after hammering so as to 
increase the length about 15 per cent. ; the observations being commenced 20 minutes 
after the hammering had been completed. 
The abscissse of the curves rejmesent the decrease of resistance on a scale of '0085 
per cent, to 1 millim., and the ordinates on a scale of one hour to the millimetre. 
* The resistance of the comparison-wire is here taken as unit. 
