618 
PROFESSOR J. A. EWING ON EXPERIMENTAL 
§ 92 and already exemplified in figs. 45 and 48, where the magnetisation reached under 
each load is plotted in terms of the load. This is done in Plate 66, fig. 53, the full lines 
of which refer to the observations made when the wire after being loaded in a mag¬ 
netically neutral state was not again subjected to the process of demagnetising by 
reversals before its susceptibility was tested, and the dotted lines refer to the corre¬ 
sponding observations made when the wire, after being loaded, was again subjected to 
the process of demagnetising by reversals. The two-curves (plain and dotted) start 
of course from the same point (at the zero of load), but within the range of magnetisa¬ 
tion and load here examined each dotted curve lies below the corresponding plain one; 
in other w r ords the process of demagnetising when loaded reduces the susceptibility. 
The load giving maximum susceptibility is slightly different in the two, being greater 
in the dotted than in the plain, and the range of difference of susceptibility under 
different loads is strikingly less in the dotted than in the plain curves, especially when 
the magnetisation is feeble. The numbers on the right of the plain curves show the 
magnetising force corresponding to each pair. 
§ 104. Up to this point the experiments on the residual effects of previous stress 
on susceptibility to subsequent magnetisation had all been made on iron wires which 
had been hardened by stretching beyond their elastic limit. It seemed desirable to 
examine in the same way a soft annealed wire, and accordingly the one already used 
in § 89 was also tested (May 24, 1882) by applying magnetising force while the load 
was kept constant. The glass-tube solenoid (§ 101) was again used, and the load was 
not allowed to exceed 6 kilos., nor to be less than 1 kilo., as in § 89. Plate 66, fig. 54, 
shows the curves of magnetisation obtained in the following four conditions :— 
O o 
First 
pair. 
Second 
pair. 
r I. Demagnetised with 1 kilo, on ; tested with 1 kilo. on. 
; II. Demagnetised with 1 kilo, on ; loaded to 6 kilos, and unloaded 
L to 1 kilo. ; tested with 1 kilo. on. 
Mil. Demagnetised with 1 kilo, on ; loaded to 6 kilos, and again 
subjected to the process of demagnetising by reversals with 
6 kilos, on ; then tested with 6 kilos, on. 
IV. Demagnetised with 1 kilo, on; loaded to 6 kilos, and the cycle 
6 — 1 — 6 performed three times, ending with 6 kilos.; then 
s. tested with 6 kilos, on. 
One kilo, of load gives a stress of 2'04 kilos, per square mm. 
We find that the 6-kilo, curve No. III. lies at first higher and afterwards lower 
than the 1-kilo, curve No. I.—a result which is entirely in agreement with the con¬ 
clusions deducible from experiments made by changing loads in a constant magnetic 
field. We find also that the two curves in each pair differ, in virtue of the residual 
effects of previous operations, in the manner which previous experiments lead us to 
expect—namely, that the process of applying reversals after the load is on reduces 
susceptibility. 
