616 
PROFESSOR J. A. EWING ON EXPERIMENTAL 
Galvanometer 
readings. 
(To reduce to 4? 
multiply by 
0*067 5.) 
Magnetometer readings. 
I. 
Demagnetised 
with no load. 
Then no-load ( nor¬ 
mal) curve. 
11 . 
Demagnetised 
with no load. 
Then 0-18*- 3. 
Load = 3 kilos. 
III. 
Demagnetised 
with no load. 
ThenO —18* —0 —3. 
Load = 3 kilos. 
IV. 
Demagnetised 
with no load. 
Loaded to IS*, 
unloaded to 3 kilos., 
and tapped 
before magnet¬ 
ising. 
Load = 3 kilos. 
V. 
Demagnetised 
with no load. 
Loaded to 3 kilos, 
and tapped 
before magnet¬ 
ising. 
Load = 3 kilos. 
0 
0 
0 
0 
0 
0 
25 
61 
22 
13 
11 , 
10 
50 
20 
70 
14 
36 
34 
75 
45 
139 
109 
103 
100 
100 
79 
198 
176 
174 
168 
125 
242 
226 
227 
219 
150 
150 
276 
265 
268 
259 
200 
212 
328 
323 
328 
320 
250 
262 
365 
369 
365 
300 
398 
398 
403 
4<i0 
350 
354 
424 
425 
429 
427 
450 
420 
461 
462 
467 
466 
588 
477 
491 
494 
499 
498 
0 
184 
274 
275 
277 
276 
Curves corresponding to cols. L, II., and III. of the above table are given in Plate 65, 
fig. 50. The table and curves show that the susceptibility, except when the magne¬ 
tisation is high, is greater with a load of 3 kilos., reached by unloading from 18-|, than 
with the same load reached by loading from zero. But columns IV. and Y. show 
that when, after each of these processes, we subject the wire to vibration before 
beginning to magnetise (it must not be supposed that there was any vibration 
during magnetisation) this difference is so much reduced as to be scarcely sensible. 
The effect of tapping is, so to speak, to blot out the recollection of previously existing 
stresses, and to make the susceptibility depend only on the actually present load. 
In addition to the observations stated above, a magnetisation curve was taken after 
the operation 0 — 18^ — 0 —18^ — 3, but this, as might be expected, 'was almost 
absolutely coincident with No. II. A repetition of the conditions of col. III. gave 
sensibly the same readings as those of col. III. 
In this experiment 3 kilos, was selected as the load under which the wire should be 
tested, because in the curves of fig. 42 the difference between the on and off curves 
is on the whole greater for 3 kilos, than for any other load. 
§ 101. Iu the experiment of the last paragraph the magnetising solenoid was wound 
directly on the iron wire, and it seemed conceivable that the wire might have been 
grasped by it so closely as to be prevented from fully responding throughout its 
whole length to the change of stress caused by loading and unloading. I did not 
think it possible that this could have occurred to such an extent as to account for 
the hysteresis of susceptibility with regard to load which had been observed, but to 
