AND STRAIN ON THE ACTION OF PHYSICAL FORCES. 
79 
case if 100 feet of the wire could be tested in the ordinary way with the catheto- 
meter, and in the second, all errors arising from the wires not being perfectly straight 
at the commencement of the experiments are entirely avoided. 
The limit of elasticity raised by previous loading. 
Robert Thalen " with, no doubt, others has shown that in the cases of iron and 
steel the limit of elasticity can be raised by previous loading. 
This was found to be so for all the metals examined, and the next experiment 
furnishes a fair example of the kind. 
Experiment XXI. 
An annealed copper wire was very carefully loaded and unloaded by allowing water 
to flow slowly into and out of a pail attached to it, and the permanent increase of 
resistance determined after each unloading. The water entered the pail from a vessel 
containing 5814 grms. of the liquid, and this quantity took five minutes to pass into 
or out of the pail. 
Number of trial. 
Number of 
measures each 
= 5814 grms. 
Number of divisions through 
which it was necessary to 
move the sliding-piece in 
ordtr to restore the balance 
after each unloading. 
1 
1 
14 
2 
1 
1 
Q 
o 
2 
31 
4 
1 
0 
5 
2 
2 
6 
3 
54 
7 
1 
0 
8 
2 
2 
9 
3 
9 
10 
4 
80 
11 
1 
0 
12 
2 
0 
13 
3 
0 
14 
4 
7 
15 
5 
122 
16 
1 
0 
17 
2 
0 
18 
3 
0 
19 
4 
0 
20 
5 
25 
21 
6 
235 
22 
1 
0 
23 
2 
0 
24 
3 
0 
25 
4 
0 
26 
5 
8 
27 
6 
29 
28 
7 
1084 
* Pogg. Ann., April, 1865, and Phil. Mag., December, 1865. 
