996 
PROFESSOR J. A. EWING AND MISS H. G. KLAASSEN 
felt. The figures show in a striking way how small the loss of energy through 
hysteresis becomes when the limits of magnetization or of magnetic force are restricted 
within certain values. 
A characteristic of the curves of fig. 5 is the remarkably uniform rate at which 
B changes with respect to H during a great part of the process of magnetic reversal. 
After the shoulder of the descending curve has been turned, by applying a sufficiently 
strong demagnetizing force, the quantity r^B/cZH takes a large and nearly constant 
value which it retains until a tolerably strong reversed magnetization has been pro¬ 
duced. The steep and nearly straight portion of the curve which corresponds to this 
part of the process has, moreover, nearly the same gradient in all except the smallest 
cycles. The same characteristic will be found in examples of annealed iron, to be 
given later, and the gradient in them is of course even steeper than it is here. In 
the present sample of steel wire (Bing II.), the maximum value of c?B/<iH is about 
4950 ; nearly half the whole magnetic change in the highest cycle occurs at approxi¬ 
mately this rate. In some of our soft iron samples c?B/c^H reaches a value nearly 
three times as great as this. 
The amount of demagnetizing force just sufficient to bring the magnetism to zero 
lias been called by Hopkinson* the coercive force. It will be seen from these tests 
that the coercive force rises progressively as the magnetization is increased. We have 
measured its values for the cycles of Bings I. and II., and these may conveniently be 
expressed in relation to the limits of H and of the intensity of magnetization I. 
Bing I. 
Limits of H. 
Limits of I. 
Coercive force. 
58-36 
1320 
4-75 
35-93 
1176 
4-55 
26-48 
1027 
4-20 
18-23 
863 
3-84 
13-01 
703 
3-59 
8-80 
539 
3-20 
6-59 
418 
2-88 
4-40 
261 
2-25 
2-91 
112 
1-46 
1-23 
22 
0-36 
* J. Hopkinson, ‘-Magnetization of Iron,” ‘ PFil. Trans.,’ 1885, p. 460. 
