166 
MR. H. TOMLINSON ON THE INFLUENCE OF STRESS 
in Thomson’s experiment on the effect of transverse magnetization on the electrical 
resistance of iron;* but when one considers the small effect of even a far larger stress 
than could have been produced by magnetization on the electrical resistance of iron, as 
shown in Table I., these objections must, I think, vanish ; and further, with nickel 
whose resistance Thomson has proved to be altered similarly to iron,f the effect of 
mechanical stress is of an opposite nature to that produced by magnetization. 
Remarks on the Nature or the Alteration oe Resistance which is 
Produced by Magnetization. 
It will be observed in Table XXXIII., in which are given the values of the increase 
of resistance produced by unit magnetizing force, that of all the metals examined 
annealed nickel is the most affected,^ and that next in order come soft iron, soft steel, 
cobalt, and bismuth. Evidently the condition of the metal may largely affect the 
susceptibility to alteration of resistance, and from what we have previously learned 
the thickness may do so also, but in a direction opposite to that which was at first 
expected, namely, that thick wires would be less affected than thin ones when the 
same B.C. and M.(J. were employed. 
Table XXXIII. 
Name of metals. 
Condition. 
Diameter 
in millimetres. 
Increase of resistance 
per unit, produced 
by unit magnetizing 
force. 
Iron. 
Annealed. . 
0-94 
2335 x10- 8 
Steel. 
Annealed . 
0-85 
1500 x10- 8 
Steel. 
Unannealed . 
2-33 
1137xl0- 8 
Steel. 
Very hard . . 
2-33 
70 x10- 8 
Nickel .... 
Annealed. 
1-05 
8070 x10- 8 
Nickel . 
Unannealed . 
7-00 
4343 x10- 8 
Cobalt . . 
Unannealed . 
7-50 
628 x10- 8 
Bismuth .... 
Unannealed . 
3-30 
21 x 10- 8 
Had the nature of the change of resistance been the same for mechanical longi¬ 
tudinal stress as for longitudinal magnetization in the case of all metals, there is nothing 
in the actual amount of alteration that might not lead us to suppose that the change 
of resistance from the latter cause is due to mere rotation of the molecules, as mole¬ 
cules, without regard to the electric currents, which, according to Ampere’s hypothesis, 
are constantly circulating round these molecules. But when we find that with nickel 
* Pliil. Trans., 1856, p. 741. 
| Proc. Roy. Soc., vol. viii., 1857. 
1 It is remarkable that the value of the “ rotational coefficient ” of nickel shonld also exceed that of 
the other magnetic metals. 
