16 
MR. H. TOMLINSON ON THE INFLUENCE OF STRESS 
an average alteration of 8*49 for 4 kilogs. Allowing for the permanent diminution of 
section, the last alteration would correspond to 8 *3 6 for 4 kilogs. on a wire of the same 
section as that previous to the second permanent elongation. 
We have, in the case of this wire, therefore, a small but decided diminution of elasticity 
produced by this amount of permanent extension, when the wire is allowed to rest 
unloaded after the extension has taken place. 
Experiment XIII. 
An annealed iron wire of the same length as the previous one was tested in the same 
manner, except that after each permanent extension it was loaded wdth a weight of 
20 kilogs., and this load was suffered to remain on the wire for 24 hours. 
Total percentage of per- 
manent extension .. J 
10 
49 
8-0 
8-9* 
Load in kilogs. 
Average alteration of length in half-millims. per load of 2 kilogs. on unit area.t 
2 
1-590 
1-571 
1-554 
1-522 
4 
1-579 
1-571 
1-514 
1-516 
6 
1-557 
1-557 
1-510 
1-494 
8 
1-544 
1-545 
1-504 
1-497 
10 
1-540 
1-537 
1-502 
1-484 
12 
1-539 
1-529 
1-495 
1-482 
14 
1-543 
1-525 
1-486 
1-482 
16 
1-515 
1-490 
1-477 
18 
1-492 
1-477 
20 
1-476 
It appears, therefore, that in the case of annealed iron the elasticity is increased by 
permanent extension if the wire be allowed to remain heavily loaded for some time 
after such extension has taken place. 
Moreover, it is remarkable that when the wire has been treated in the above- 
mentioned manner the average alteration per unit load diminishes * as the load 
* The wire was broken at a point about 3 inches from the scalc-pan by this last extension. 
t The unit area is assumed to be the area of the section of the wire after the last permanent extension; 
this area was '00137 square centim. 
t [Note added April, 1882.—It should be stated here that a load of about 6 kilogs. (not included in 
the loads given) was left permanently on the wire. I have since found by an indirect method (see 
Part II.) that, if the wire be entirely relieved from stress before beginning to test for the temporary effect 
of loading, the temporary elongation increases with the first few loads in greater proportion than the 
latter. We may say, therefore, that in the case of iron wire which has suffered very considerable per¬ 
manent extension and afterwards been allowed to rest for some time either unloaded or loaded, the ratio 
of the temporary elongation to the load producing it first increases with the latter to a certain limit, then 
diminishes to a second limit, and finally begins to increase again. If, however, the wire has during the 
interval of rest been heavily loaded, the first limit is reached more quickly than is the case when the wire 
has rested unloaded; so that if, as in this instance, it is necessary to leave even a comparatively small 
