72 
MESSRS. G. F. C. SEARLE AND T. G. BEDFORD 
Ho. 
2-50 
4-98 
7-57 
10-86 
14-70 
20-05 
Percentage change in 
17-1 
11-0 
3-1 
2-0 
-9 
-4 
Percentage change in 
W . 
27-5 
17-0 
) 
11-0 
5 • 5 
3-7 
1-9 
§ 48, Soft Iron demagnetised “ hy Reversals.”* —The same piece of wire and the 
same key were used as in § 47. The wire was very completely demagnetised by 
reversals before the tests for Bq and W were made ; a mirror magnetometer served 
as indicator. The results are shovii in the table below 
No. 
Ho = 
2-.50. 
Ho = 
7-45. 
Ho = 
20-50. 
Bo. 
Bo. 
W. 
Bg. 
M'. 
1 
1 
2068 
711 
9950 
8000 
13480 
16670 
2 
1997 
662 
9980 
8000 
3 
1984 
669 
9960 
8000 
4 
1997 
652 
11 
1960 
638 
9940 
7910 
13510 
16590 
21 
1960 
633 
9940 
7850 
41 
1950 
613 
9890 
8000 
13510 
16580 
81 
1913 
603 
13480 
16610 
101 
9900 
7820 
1 
For Hq = 7'45 and Hg = 20'50 the values of Bg and W are constant within the 
errors of observation. For Hg = 2'5 there is a considerable diminution in both Bg 
and W during the first 41 cycles, but much less than in the case of the wire 
demagnetised by annealing, the changes in the first 41 cycles being now for Bg 
5'8 per cent., and for W 13‘8 per cent. 
The wire had been annealed before the tests for H = 2’5 in §47 were made. 
Without further annealing, the tests of the present section for Hg = 7‘45, 20'50, 
and 2'5 were made in the order written. This treatment has had the result of 
diminishing the initial value of Bg and raising its value after 41 reversals ; the value 
of W is at the same time considerably increased. 
§ 49. Steel Rod. —A few experiments were made upon a steel rod ’0925 sq. centim. 
in section, using the key of § 31. We endeavoured to demagnetise it by reversals 
before the tests for Bg and W were made, but we were only partially successful. The 
dynamometer was not sensitive enough to enable us to go to small magnetising 
forces. The induction remained practically constant for both values of Hg ; in 41 
cycles the hysteresis fell by 10 per cent, when Hg = 7'29 and by 2’5 per cent, when 
* See Ewing, ‘ Magnetic Induction . . .,” 3rd Edition, fig. 155. 
