MAGNETISATION ON THE THERMOELECTRIC QUALITY OF IRON. 
367 
of the load. The influence of hysteresis is still observable, though to a far less degree 
than when the wire was undisturbed. The change caused by vibration will be best 
understood by considering the figs. 10a and 10b in their relation to the curves which 
have been already given for the complete cycle of loads, 0 — 21—0. 
§ 15. In another experiment the influence of vibration in removing the accumulated 
effect of hysteresis was examined as follows:—The wire was loaded, without vibration, 
to 9 kilos. The galvanometer deflection, measuring the thermoelectric current, was 
then —99. Then, with the load of 9 kilos, kept constant, the wire was vigorously 
tapped, and the deflection changed to —144. Next the load was increased to 
21 kilos, and then reduced to 9 kilos. The deflection was then —175. On tapping 
the wire, with the load of 9 kilos, kept constant, this changed to —150. Thus the 
total difference due to hysteresis of 175 — 99 or 76 scale-divisions was reduced by 
tapping to 6 divisions. 
§ 16. In a supplement to his original communication to the Royal Society in 1881, 
the writer described a further experiment which showed that changes of magnetisation 
had an effect like that of vibration in removing the influence of hysteresis in the 
relation of thermoelectric quality to stress. When a constant load was applied, and 
the wire was gently stroked along its length by a bar magnet, the thermoelectric 
current changed in much the same way as it would have changed had the wire been 
subjected to a comparatively violent amount of mechanical disturbance, and to a 
degree much greater than could be explained as due to the slight mechanical 
disturbance caused by contact with the magnet. The influence of magnetisation, both 
in this and other respects, has formed the subject of many other experiments which 
will be described in the sequel. 
§ 17. So far, only those results have been stated which were mentioned in the 
paper, “ Part I.,” communicated to the Royal Society in 1881. Figs. 1 to 10 inclusive 
have been copied from that paper. It remains to describe later experiments, made 
for the most part in 1883. Their principal object has been to examine the relation 
between the effects of stress on thermoelectric quality, on the one hand, and on 
magnetisation on the other. A glance at the figures given here and at those given 
elsewhere,* to illustrate the changes of magnetism produced by loading and unloading 
an iron wire, will show that there is a very striking likeness between them; enough 
likeness, in fact, to make the hypothesis very natural that stress acts on the thermo¬ 
electric quality of iron by altering its magnetisation, and that the variations of 
magnetism are the immediate cause of thermoelectric change. In the writer’s earlier 
experiments no precautions were taken to rid the iron of magnetism to begin with, 
nor to place it in a position where it would escape magnetisation by the terrestrial 
field, and it was certainly in a more or less magnetic condition throughout the 
experiments. Sir W. Thomson has shownt that change of magnetism does give rise 
* Phil. Trans., vol. 176 (1885), Plates 62, 63; Proc. Roy. Soc., vol. 34 ^1882) pp. 43, 44. 
t Ilicl., vol. 146 (1856), p. 722, § 134. 
