50 
MR. H. TOMLINSON ON THE INFLUENCE OF STRESS 
Experiment VII. 
An annealed iron wire which had been loaded for 24 hours with 30 kilogs. 
Number of kilogs. 
in load. 
Temporary alteration 
of resistance. 
Average alteration 
per 2 kilogs. 
Difference between 
consecutive averages. 
2 
9'0 
9-00 
4 
20-5 
10-25 
1-25 
6 
32-2 
10-73 
•48 
8 
44-0 
11-00 
•27 • 
10 
56-3 
11-26 
•26 
12 
68'5 
11-42 
■16 
14 
80-8 
11-54 
12 
16 
92-9 
11-61 
•07 
18 
105T 
11-68 
•07 
20 
1174 
11-74 
•06 
22 
129-8 
11-80 
■06 
24 
142-3 
11-858 
•058 
26 
155-0 
11-92 
•062 
Remarks on Experiments I.-VII. inclusive. 
All these experiments prove that the ratio of the resistance-increase to the load is 
not quite constant, but that the former increases in a greater proportion than the 
latter. This want of proportionality is seen from Experiments I.-IY. inclusive to be 
materially diminished, though never entirely made to vanish, by repeated heavy 
loading and unloading, and it appears impossible to find any single formula which 
will express exactly the relation between the load and the alteration of resistance for 
all conditions of the wire ; consequently the values of x given in Table I. are calculated 
from observations made with two weights, the larger never exceeding one-fourth of 
the “ breaking-weight,” and being twice the smaller; and the mean of the two 
numbers obtained by dividing the observed alteration by the load is taken to 
represent the change produced by unit load, this mean being in no case different 
from either of the numbers by more than 1 per cent. 
The columns in which are recorded the differences between the consecutive average 
alteration per kilogramme show that when the load employed in determining the 
temporary alteration of resistance approaches closely to the highest load which has 
been used in the preliminary operations, a comparatively rapid increase takes place 
in the ratio of the temporary alteration of resistance to the load. 
From Experiments VI. and VII. we learn that in the case of a metal which has 
been rendered very hard by the process of drawing, or in the case of iron* which has 
been subjected to a heavy load for some time, the average alteration of resistance per 
* Probably also in the case of any metal possessing a coercive force comparable with that of iron. 
