AND STRAIN ON THE ACTION OF PHYSICAL FORCES. 
G3 
Experiment XII. 
An annealed nickel wire loaded and unloaded several times on three different 
occasions, with weights of 18, 20, and 22 kilogs. respectively, and then tested with 
equal or lesser loads. 
Load in kilogs. 
put on and off several 
times = o. 
18 ^ 
I 
L 
20 
/ 
l 
Load used in 
testing after a=/3. 
Temporary 
alteration of resistance 
produced by 13. 
— Decrease of resistance. 
+ Increase of resistance. 
Time after 
using a at which /3 
was applied. 
First 8 
Next 10 
First 8 
Next 10 
First 8 
Next 10 
First 8 
Next 12 
First 8 
Next 12 
First 8 
Next 12 
First 8 
Next 12 
-89 
-95 
+ 60 
-99 
+ 57 
-79 
+ 71 
-82-5 
+ 67-5 
-72-0 
+ 6+5 
— 73 5 
+ 62 - 5 
j hour. 
1 „ 
24 hours. 
1 hour. 
7 hours. 
\ hour. 
12 hours. 
We see here that rest produces a very appreciable effect, increasing the negative 
alteration of resistance and diminishing the positive alteration; but we notice also 
that as the loads a become larger and larger the influence of rest becomes less and less 
marked ; and, lastly, that as a increases to nearly the breaking load of the wire the 
effects both of the moderate load to produce decrease and of the excessive load to pro¬ 
duce increase become more and more equal, and if we turn to Table V. we see plainly 
that the points in the curves showing the position of maximum decrease of resistance, 
which at first become wider and wider apart, at length begin to close up. 
All this is intelligible if we bear in mind what has been proved in Part I., namely, 
that the‘elasticity of all metals is diminished by permanent extension carried to a 
certain point, and beyond this point increased, and provided that we assume that 
temporary elongation without regard to the stress producing it causes increase of 
resistance. The question then naturally arises, do stress and the consequent 
temporary strain produce on the electrical conductivity of substances opposite effects ? 
* Permanent elongation we stall find produces in most metals first increase of specific resistance and 
tfien decrease, but in iron and nickel first decrease and then increase. 
