10G 
MR. H. TOMLINSON ON THE INFLUENCE OF STRESS 
Table XVII.—Curves showing the permanent alteration of specific resistance 
produced by permanent torsion. 
Remarks on Table XVII. 
The effect of torsion on the specific resistance is evidently of a similar nature to 
that of the effect of permanent extension and hammering, but the amount of alteration 
shown at the turning point of the curves is in all cases much less than that observed 
at the turning points of the curves exhibiting the results of hammering and extension. 
In the case of iron, the first torsion applied increases the specific resistance, but further 
torsion acts in the same direction as the strain caused by hammering ajid extension, 
i.e., diminishes the specific resistance up to a certain point, but beyond this point 
increases it. It may be that the increase produced in iron by the first few turns is due 
to magnetic influence on the resistance, for as Thomson has observed," the electric 
current instead of flowing rectilineally along the wire would flow in helical lines, and 
would therefore increase the resistance by longitudinal magnetization.t 
* W. Thomson, “ Electroclynamic Qualities of Metals,” Pliil. Trans. 1879, Part I., § 229. 
f W. Thomson, “ Electrodynannic Qualities of Metals,” Pliil. Trans. 1856. Bakerian Lecture, § 146, 
and H. Tomlinson, Proc. Roy. Soc., June 17, 1875. [Note added May, 1882.—I have since found that 
very slight extension increases the specific resistance of iron, and am therefore inclined to reject the 
above hypothesis, and to believe that very slight strain of any kind increases the specific l'esistance.] 
