150 
ME. H. TOMLINSON ON THE INFLUENCE OF STRESS 
The Effect of Longitudinal Magnetization on the Electrical Resistance 
of a Bar of Nickel. 
Experiment LXIX. 
A bar of nickel, 8 - 3 centims. long and 70 centim. in diameter, was soldered to two 
stout copper terminals, whilst a similar bar, similarly provided, served as a comparison 
piece. The bars were arranged in the same manner as the steel bars in the last experi¬ 
ment, but the magnetizing coil B was used instead of A. Before placing the nickel in 
B it was covered with several layers of stout caoutchouc, and the comparison piece having 
been furnished in like manner, the usual precautions of well covering both bars were 
taken. The B.C. was furnished by two Grove’s cells and the M.C, by eight Grove’s 
cells with adjustable external resistance. The circuit of the B.C. was kept closed, and 
the alteration caused by magnetization in the resistance of the bar was measured by 
the deflection of the image of the illuminated wire on the scale." 
As the resistances to be compared are in this case very small, it is advisable to show 
how far any measurements of alteration of resistance can be depended upon, and for 
this purpose the first set of readings with the smallest M.C. are given :— 
Total deflection caused by 
passing the M.C. in terms of 
divisions of the galvanometer- 
scale. + signifies increase 
of resistance.! 
Number of trial. 
+ 8-50 
1 
+ 8-25 
2 
+ 7-00 
3 
+ 6-25 
4 
+ 775 
5 
+ 8-50 
6 
+ 8-00 
7 
+ 9-00 
8 
+ 8-25 
9 
+ 7*75 
10 
+ 7-25 
11 
+ 7*9 
Mean. 
* In this, and in every otter instance in which such a mode of measuring alteration of resistance was 
adopted, the direct action of the magnetizing coil and of the included metal core on the galvanometer 
when the latter was not in circuit was always determined by a separate set of experiments, as though such 
action was small, it could never he entirely avoided. The distance (several yards) of the coil from the 
galvanometer was however such that no perceptible difference in the sensibility of the latter was introduced 
when the M.C. was closed. Similar remarks apply to the tangent galvanometer, and the readings given 
are in the case of both instruments always corrected for the above mentioned direct action. For the mode 
of taking the readings see Experiment LXXI. on Bismuth. 
t Each number is calculated from three consecutive readings in the manner described in 
Experiment LXXI. 
