134 
MR. H. TOMLINSON ON THE INFLUENCE OE STRESS 
Beetz and Chwolson both confirmed the results of Thomson as far as longitudinal 
magnetization was concerned ; but with the former of the two first observers an experi¬ 
ment where transverse magnetization was employed, ended in giving purely negative 
results. The values obtained in my own experiments differed considerably from those 
of Thomson as regards amount and in the case of hard steel also in nature. Moreover, 
it appeared that the circular magnetization which ensues when a current is passing 
through an iron wire caused an increase of resistance, and as we might perhaps expect 
circular magnetization to cause a similar effect, as regards nature, on the conductivity 
to transverse magnetization, 4 ' these results were not in accordance with those of 
Thomson. Unfortunately I had not at the time read Sir W. Thomson’s paper, and 
investigations made in later years convinced me that the observations recorded in my 
“ Preliminary Notice ” were not reliable, partly because alteration of resistance from 
change of temperature had not been sufficiently guarded against, and partly because of 
a “ Peltier effect,” which I have since found would, with the large battery-power 
employed in the circuit of the “Wheatstone’s bridge” arrangement, vitiate the 
results. To my astonishment, Auerbach, three years afterwards, published an essayt 
“ On the Passage of the Galvanic Current through Iron,” in which my own observa¬ 
tions both as regards the magnitude and nature of the changes produced in iron and 
hard and soft steel by longitudinal magnetization were apparently fully confirmed. 
Moreover, it appeared that he also agreed with me that circular magnetization caused 
increase of resistence in iron ; and ingeniously reasoning that, this being the case, feeble 
longitudinal magnetization should decrease the resistance of iron, brought forward a 
series of experiments which seemed fully to bear out his views. Under these circum¬ 
stances it seemed to be advisable to retry some of my old experiments on iron and steel 
rods, and further to extend the enquiry to wires of iron and steel. 
As several of the instruments used in this part of the investigation have also been 
employed in several experiments yet to be described in the other parts of this paper, 
it seems advisable to give here some description of them, as well as certain data which 
will be required for converting the measurements taken into absolute units. 
The tangent galvanometer. 
This was of the usual Helmholtz-Gaugain pattern, made by Elliott Bros., where 
there are two stout copper rings for measuring currents where it is desirable that the 
resistance of the galvanometer should be small, and three pairs of coils of finer wire 
for other purposes. In these investigations the former only were employed, and 
therefore we may consider tire resistance of the galvanometer itself to be neglectable. 
* This, however, is not, I believe, the case. 
t Phil. Mag., July, 1879, vol. viii., p. 1. Translated from the original essay (Leipzig, 1878), com¬ 
municated by the author. 
