140 
ME, H. TOMLINSON ON THE INFLUENCE OF STRESS 
“ throw ” of the needle, both with and without the RC. flowing through the nickel. A 
preliminary set of observations had given the means of determining the amount of 
current which would be induced when the nickel was not in the coil, and, therefore, by 
subtraction the induced currents due to the nickel only could be determined. The 
glass tube and the fine silk-covered copper wire on it would have served to shield the 
nickel from any change of temperature likely to be caused by the magnetizing current; 
but as a further precaution, the solenoid was well wrapped up in paper so that it 
would just fit inside the coil A, The comparison-wire w^as also surrounded with glass 
and caoutchouc tubing, and, as with the iron, the whole arrangement was well covered 
over with baize. 
The following values (Table XXVI.) of the alterations of resistance are the means of 
five or six trials with each of the various magnetizing forces employed. 
Table XXVI. 
M.O. 
in divisions of 
the scale of 
the tangent 
galvanometer 
a. 
Throw of the 
galvanometer 
needle due to 
induction current 
caused by- 
magnetization 
of the nickel when 
the load on the 
wire = 0 kilog. 
P- 
Increase of 
resistance in terms 
of division of 
the platino-iridium 
wire when the 
load on the wire 
= 0 kilog. 
y • 
a 
y 
p‘ 
Increase 
of resistance 
calculated 
from 
the formula 
y = a.a + b.fi 
a = -2992 
6=1514. 
Increase 
of resistance 
caused by 
magnetism 
with 
2 kilogs. on 
the wire. 
Increase 
of resistance 
caused by 
magnetism 
with 
6 kilogs. on 
the wire. 
Increase 
of resistance 
caused by 
magnetism 
after the 
removal of 
the 6 kilogs. 
and after 
a rest of two 
days. 
19 
87 
7-0 
•368 
■805 
7'00 
6-0 
2-0 
8-6 
35 
16-2 
12-4 
•354 
•765 
12-92 
53 
25-6 
19T 
•360 
•746 
1973 
69 
31-0 
24-6 
•356 
•781 
25-30 
24-5 
19'8 
331 
86 
36-8 
31-3 
•364 
■851 
31-30 
159 
56-4 
57-0 
•358 
1-011 
56T0 
53-0 
45-0 
80-0 
279 
81-5 
95'8 
•343 
1175 
95-80 
99T 
85-2 
131-0 
It is evident from the last experiment that the increase of resistance which can be 
produced by magnetizing nickel wire longitudinally is diminished by temporary longi¬ 
tudinal stress not carried beyond a certain limit, provided the magnetizing force does 
not exceed a certain critical value depending upon the amount of stress applied. 
Thus we see that when the value of a is somewhere between 159 and 279, the load of 
2 kilogs. begins to increase the alteration of resistance caused by the magnetization. 
Now, Sir W. Thomson has proved'"—and in the case of this particular wire I have been 
able to verify the factt—that with nickel the magnetism induced by any magnetizing 
force is increased or diminished by stress according as the magnetizing force does or 
does not exceed a certain critical value. With iron, on the contrary, the induced 
* “ Electrodynamic Qualities of Metals ”—Part VII., Phil. Trans., Part I., 1879. 
f I shall have occasion to refer to this experiment in Pai’t III. of my paper. 
