144 
MR. H. TOMLINSON ON THE INFLUENCE OF STRESS 
Experiment LXIII. 
An annealed iron wire, '094 centim. in diameter, was arranged with the same pre¬ 
cautions and in the same manner as the nickel wire in the last experiment; but as it 
was found difficult to make observations in the ordinary way in consequence of the 
Villari’s “ shock-currents” being very pronounced, the B.C., for which one Grove’s 
cell was employed, was kept flowing until the wire and the comparison-wire had 
assumed a sufficiently stable resistance-ratio which was very nearly equal to unity. 
The alteration of resistance produced by various magnetizing forces was measured by 
the deflection of the image of the illuminated wire on the scale, and the mode of 
taking the readings and the nature of the corrections to be applied for the direct 
action of the magnetizing coil on the galvanometer are described in Experiments 
LXTX. and LXXI. 
The following table contains the results of this experiment 
Table XXVITI. 
M.C. in 
divisions of the 
scale of the 
tangent 
galvanometer. 
a. 
Throw of the 
galvanometer 
needle due to the 
induction current 
caused by the 
magnetization of 
the iron. 
B.C. flowing. 
(S. 
Throw of the 
galvanometer 
needle due to the 
induction current 
caused by the 
magnetization of 
the iron. 
B.C. not flowing. 
/s'. 
Increase 
of resistance 
in terms of 
divisions of the 
galvanometer 
scale. 
7- 
a 
y 
P 
/s 
A 
Increase of 
resistance 
calculated from 
the formula 
y = a.n + b.i3 
a = -0397 
£> = ■106. 
21 
20 
17 
1-9 
•091 
' -095 
1-18 
2-9 
43 
56 
42 
5-0 
•116 
•090 
133 
7-7 
82 
107 
71 
1ST 
T60 
1-220 
1-51 
14-6 
130 
134 
91 
193 
T48 
1-440 
1-47 
19-4 
203 
153 
103 
23-9 
118 
1-562 
1-49 
23-9 
383 
200 
36'9 
•096 
1-845 
36-4 
519 
220 
172 
43-9 
•085 
2-000 
1-28 
43-9 
Table XXVIII. shows that with iron as with nickel the increase of resistance can be 
represented by the formula y=a.a-\-b./5 ,* and, here again therefore, it seems as if the 
alteration of resistance would go on increasing as the magnetizing force increased even 
when there would be no perceptible increase of induced magnetism. The cases of iron 
and nickel, however, differ considerably in one respect, namely, that whereas with the 
latter metal the magnetizing force played the more important part in altering the 
* The discrepancies between the observed and calculated values of 7 for the first three magnetizing 
forces is, I believe, almost if not entirely due to the fact that, unfortunately, before any exact measurements 
had been made with the lower values of a, the full magnetizing force had been employed. This would 
not perhaps have affected the result, as far as the agreement between observation and calculation is 
concerned, had the induced magnetism been measured at the same time as the alteration of resistance, 
but this was not the case. 
