1000 
PROFESSOR J. A. EWINO AND MISS H. G. KLAASSEN 
Ring III.—Thick Sheet Iron : Values of | H dl and Coercive Force. 
Number of cycle. 
Limits of H. 
Limits of B. 
Limits of I. 
iHtt 
Coercive force. 
1 
32-34 
15920 
1265 
13960 
2-10 
2 
21-60 
14920 
1187 
12050 
2-10 
3 
14-62 
13730 
1092 
10240 
2-10 
4 
10-42 
12460 
991 
8550 
2-01 
5 
8-05 
11340 
902 
7270 
1-96 
6 
5-59 
9520 
757 
5240 
1-79 
7 
4-01 
7790 
620 
3760 
1-61 
8 
2-89 
5830 
464 
2270 
1-44 
9 
2-05 
3720 
296 
1130 
1-20 
10 
1-32 
1360 
108 
230 
0-69 
11 
0-76 
400 
32 
, , 
0-28 
12 
0-45 
170 
14 
• • 
0-12 
The values of | H dl, in relation to B, will be found plotted in fig. 21 , along with 
corresponding results for other samples of sheet and wire iron. 
The next sample to be tested (Bing IV.) was of thin sheet iron, which, like the 
last, had been supplied to form the core of a dynamo armature. This iron, though 
supplied for a purpose in which magnetic softness is important, did not compare 
favourably with the thick sheet of Bing III. The ring was built up of 30 flat annuli, 
which were turned out of larger punched discs. The thickness of the sheet varied in 
different discs from 0‘044 to 0‘050 centim. The external diameter was 10'9 centims. 
and the internal diameter 8'45 centims., and the mean thickness of the sheets was 
0'47 millim. The discs were insulated from one another with paper. Nine cycles 
were measured in the first instance, and then six small cycles, with a larger induction 
coil and a more sensitive adjustment of the current galvanometer. The results are 
given numerically below, and graphically in figs. 11 and 12. The larger cycles, with 
the exception of the second, are drawn on fig. 11. Fig. 12 exhibits the small cycles. 
The induction coil used in measuring the large cycles had 12 turns, but in the small 
cycles a coil with 195 turns was used to give a large magnification of the ballistic 
readings, the sensibility of the ballistic galvanometer itself being unchanged. The 
curves of the small cycles have been determined in this instance with particular 
minuteness, as a study of tlie behaviour of the iron under reversals of weak 
magnetizing forces. In the lowest cycle the limits of the magnetizing force are 
so narrow that the condition is approaching that of quasi-elastic magnetization : 
there is, however, still a distinct trace of hysteresis. 
