70 
MERSES. G. F. C. SEARLE AND T. G. BEDFORD 
sq. centim. An ordinary mercury rocking key was used, and the choking coil was 
inserted in the circuit. 
We now give the results of one of these experiments. The numbers heading the 
columns indicate the cycle to which the pair of semi-cycles in any column belong. 
Cycle. 
1. 
9 
3. 
4. 
5. 6. 
28. 
50. 
^ for -t-Ho to - Hq 
5440 
4820 
4650 
4570 
4480 4470 
4260 
4190 
1 Hf/B for - Ho to + 
in J 
4540 
4380 
4290 
4230 
1 
4210 4160 
4030 
3990 1 
1 
In this example the inequality is greater and more persistent than in most cases. 
The inequality is generally much more marked for small than for large magnetic 
forces. It will be noticed that the hysteresis diminishes with continued reversals."^ 
Efect of Continued Reversals. 
§ 46. In the course of the experiments undertaken in the hope of finding the cause 
of the inequality of the two throws of the dynamometer, 6^ and do, for the two semi¬ 
cycles belonging to a single cycle, we had occasion to put the sjjecimen through many 
cycles. We then discovered that the hysteresis diminishes very considerably with 
continued reversals of the magnetic force. To investigate this matter more com¬ 
pletely a systematic set of experiments was made in 1899 with the object of 
determining how the effect depends upon the limits of the magnetic force. The 
experiments were carried out in the following manner:—The specimen, demag¬ 
netised by annealing or “ by reversals,” was placed in the solenoid when no current 
was flowing. The magnetic force was first applied in the positive direction ; the 
magnetic force was then reversed from Hq to — Hq and the throws of the dyna¬ 
mometer and the galvanometer were read simultaneously. The next reversal — Hq to 
Hq was observed in like manner. These two reversals constituted the first cycle. 
The observations were repeated for other cycles as shown in the tables, where in each 
case the first column shows the number of the cycle. The two throws of the 
dynamometer, dj and d^, sometimes showed an inequality which was rather persistent, 
though it was never greater than that recorded in § 45. We have therefore thought 
it sufficient to give the value of the hysteresis deduced from each complete cycle. 
The mean maximum magnetic induction, Bq, which diminished in much tlie same 
manner as the hysteresis, is also recorded in the tables. 
* The initial asymmetry of the hysteresis loop and its gradual shrinking Muth continued reversals are 
well shown in fig. 154 in Professor Ewing’s Magnetic Induction . . .’, 3rd Edition. Much labour would 
have been saved had we realised the significance of Professor Ewing’s curves. 
