132 
MR. H. TOMLINSON ON THE INFLUENCE OF STRESS 
Table XXV. 
Metal. 
Percentage temporary alteration of elasticity 
caused by raising the temperature from 
15° C. to 100° C. + signifies increase of elasticity 
produced by rise of temperature. 
Percentage increase of 
alteration of resistance caused 
by raising the temperature 
from 15° C. to 100° C. 
— signifies decrease of 
alteration. 
Wertheih. 
Tomlinson. 
English steel wire . 
+ 23'20 
-2-58 
Iron wire. 
+ 6-91 
-1-64 
+ 570 
Copper. 
- 6'59 
-474 
+ 1-87 
Nickel. 
-8-41 
-50-00 
Remarks on Experiments LV.-LVIII., and on Table XXV. 
It appears from the last experiments that there is really a permanent increase of 
elasticity produced in annealed iron and steel by merely raising the temperature to 
100° C. ; and what is still more remarkable, there was in the case of one specimen of 
iron wire, which was so ductile as to lengthen by 24 per cent, before breaking,* such a 
large loss of ductility that its maximum permanent elongation barely reached 13 per 
cent, after it had been heated to 100° C. and allowed to cool again. As the last 
discovery was made when experimenting on the effect of permanent extension on the 
susceptibility of the resistance of iron to change of temperature, it was thought at 
first that the passage of the current used in determining the electrical resistance might 
have some influence on the ductility, but on heating three other pieces of the same 
wire to 100° C., and afterwards allowing them to cool without permitting any current 
to flow through them, almost exactly the same change was observed ; and yet in all 
these cases the rate of cooling was slow; so much so, indeed, that with the last specimen 
employed, in which special precautions had been taken to surround the small air chamber 
in which the wire was heated with several coatings of baize, the chamber was sensibly 
warm to the touch 12 hours after the cooling had commenced. How far other kinds of 
annealed wrought-iron might show a change of ductility from like cause I know not, 
but it seems evident that changes comparatively enormous can be produced in the 
elasticity and ductility of this metal by small alterations of temperature. 
It has also been shown by Experiment XXXIX. that the electrical conductivity of 
annealed steel is increased by heating slightly and then cooling quickly, and it will be 
proved in Parts III. and IV. that there is a correspondingly large effect on the magnetic 
inductive capacity and on the thermo-electric properties of steel produced by the same 
process. It would appear, therefore, that researches of this kind might lend valuable 
* This wire I received through the kindness of Mr. J. T. Eottomley, and was especially prepared for 
experiments on magnetic induction carried on in the physical laboratory of Sir W. Thomson. 
