GOG 
PROFESSOR J. A. EWING ON EXPERIMENTAL 
Effects of Stress on a Stretched Iron Wire in Constant Magnetic Fields, Plate 63, 
fig. 42. 
(1) 
Mag¬ 
netising 
field, 
b- 
(2) 
Initial 
(S) 
This was 
changed . 
Difference 
Cyclic effects of 18*5 kilos. 
Value of load in kilos giving 
maximum of 15. 
No. of 
curve. 
3 
value of 
before 
loading. 
by first 
appli¬ 
cation of 
18‘5 kilos, 
to 
(3)-(2) 
showing 
effect of 
first on. 
Value of 
3 
for off. 
Value of 
3 
for on. 
Difference 
on — off 
During 
first 
loading. 
During 
cyclic on. 
During 
cyclic off. 
i. 
0 - 34 
7 
75 
68 
110 
183 
73 
14 
10 - 7 
7 - 0 
ii. 
2 - 49 
50 
590 
540 
463 
614 
151 
11 
98 
6 - l 
in. 
5 - 75 
195 
740 
545 
642 
748 
106 
10 
9 - 6 
5 - 9 
IV. 
8 - 6 
372 
842 
470 
776 
845 
69 
9 - 8 
9 - 5 
5 - 7 
V. 
11-6 
527 
907 
380 
870 
910 
40 
9 - 6 
9-4 
5 - 4 
VI. 
20-1 
875 
1045 
170 
1115 
1045 
- 70 
8 - 4 
8 - 2 
4 - 7 
VII. 
34 - 0 
1185 
1140 
- 45 
1270 
1141 
-129 
4-8 
Xo maxi¬ 
mum. 
1 
The numbers in column (2) are the values of 3 reached by applying each magnetic 
field to the previously demagnetised wire. They correspond to the starting points of 
the dotted lines in fig. 42. 
By comparing figs. 40, 41, and 42, as well as from fig. 36, we see that the position 
of the maximum point is shifted out (that is, towards higher values of the load) the 
more the wire is stretched. It is not, however, shifted out so far as to prevent the 
descending (right hand) limb of the curve from becoming relatively larger as the 
range of loading is extended by successive stretchings. This limb is most prominent 
in fig. 42, where the range of loading is extended to 18'5 kilos., although the maximum 
points occur there at higher loads than in figs. 40 and 41, in which the amount of 
stretching was less. 
§ 89. Similar Experiment with a Soft Annealed Wire. — Only one more 
experiment of the same class as the foregoing need be referred to in detail. It 
was made (May 26, 1882) on another specimen of the same kind of iron wire 
as before (0‘79 mm. diameter and 33 centims. long) to test the effects of load 
in various magnetic fields when the wire was in the soft annealed state. The wire 
was carefully annealed and surrounded by two solenoids, in one of which a current 
was maintained which neutralised the vertical component of the earth’s field, while 
the other was used to give the desired magnetising force. The wire (whose limit of 
elasticity was pretty sharply defined at 10 kilos.) was never loaded with more than 
6 kilos., and instead of reducing the load to zero in each cyclic application, a load of 
1 kilo, was kept always on, in order to avoid errors due to local bending and unbend¬ 
ing - , which are much more Table to occur when we are dealing with annealed wire 
than with wire which has been well straightened by stretching. The process ol 
experiment was in other respects the same as before. Before the application of each 
magnetising field the wire was demagnetised by reversals (with 1 kilo, on), then the 
