RESEARCHES IN MAGNETISM. 
571 
showing the relation of 33 or 2> to <§, the same thing exhibits itself in what may be 
called the over-closing of loops formed by removing and re-applying a given value of 
A good example of this is furnished by Plate 60, fig. 17, which shows how 
much more considerable the action now spoken of is at early than at late stages 
of the magnetisation. 
The following experiment (also on annealed iron) shows that the same kind of 
action occurs when the current is slowly changed by the slide of § 18, and the 
magnetism is determined by a magnetometer. 
Magnetising Current. 
4 
Magnetometer 
Deflection. 
s. 
Gradually raised to . 
. 70 
2-46 
93 
298 
,, reduced to . . 
. 0 
0 
65 
208 
,, raised to . 
. 70 
2-46 
97 
310 
,, reduced to . 
. 0 
0 
70 
224 
Tlien 100 sudden makes and breaks— 
Suddenly raised to . 
. 70 
2-46 
103 
330 
,, reduced to . 
. 0 
0 
80 
256 
§ 55. Effects of Repeated Reversal of Magnetising Force. —When a magnetising force 
is applied and then repeatedly reversed, the changes of magnetism, instead of being 
strictly cyclic, form what may be termed unclosed loops. Instances of this are given 
by a number of the preceding figures, especially by Plate 60, fig. 16, which shows a 
series of these unclosed loops in the magnetisation of steel wire. The result is, as in 
the former case, that successive repetitions of the process give a gradually diminishing 
range of magnetic change. This action, like the last, occurs most conspicuously at 
points in the early part of the curve of magnetisation. The following observations 
were made specially to exhibit it, on a piece of annealed iron wire, 400 diameters 
long, by the magnetometric method. 
Magnetising Current. 
Magnetometer. 
0 
0 
Gradually raised to . 
+ 190 
+ 146 
0 
„ reversed to . 
-190 
-141 
5» 55 55 
+ 190 
+ 127 
[Here there is gradual diminution of range, 
f This part of the operation is shown in fig. 26. 
55 55 55 
-190 
-133 
55 55 55 
+ 190 
+ 120 
55 55 55 
-190 
-132 
Suddenly „ „ . . 
+ 190 
-190 
+ 190 
+ 124 
-136 
+ 123 
Here there is an increase of range due to the 
55 55 5 5 » 
’5 55 55 
f suddenness of these reversals. 
Fifty double reversals, then 
Suddenly reversed to 
+ 190 
+ 111 
1 
But after repeating the sudden reversals often 
-190 
-127 
J 
enough the range becomes smaller than ever. 
Then gradually „ . . 
+ 190 
+ 108 
And a gradual repetition of the cycle causes 
55 55 55 
-190 
-126 
still a further reduction of range. 
