572 
PROFESSOR J. A. EWING ON EXPERIMENTAL 
In the first part of the above operations, during the five gradual reversals of 
magnetising force, intermediate readings were taken, which enabled the curves shown 
in Plate 61, fig. 26, to be drawn. These show at a glance the manner in which the 
range of magnetic change diminishes. Sudden reversals, following on these, cause at 
first an increase of range, thus illustrating the comparative effects of gradual and 
sudden change of <§, but on being repeated many times they reduce the range to a 
lower value than before. 
§ 56. The same piece of wire was next subjected to a magnetising force about 
fire times greater than the above, and was then demagnetised by reversals (§ 19). 
Experiments similar to the above were then made on it, when it was found that the 
tendency to a diminution of range with repetition of a cyclic alteration of magnetising 
force had disappeared. The diagram, Plate 61, fig. 27, shows the effect of applying, 
reversing, and reapplying the same magnetising force as in the former case, after the 
wire had been demagnetised by reversals. It shows that the changes of magnetism 
are now cyclic. The same result was given by other specimens, which when freshly 
annealed gave much diminution of range, but when demagnetised by reversals after 
the magnetising force had been raised to a high value, were found to have lost this 
property. In this respect, then, a wire demagnetised by reversals differs from the 
same wire in its primitive annealed state. It will be seen, too, by comparing figures 
26 and 27, that the unsymmetrical susceptibility with respect to forces of opposite 
signs which exists in the annealed wire has given place to a very perfect symmetry 
after demagnetisation by reversals. Pe-annealing the wire restored all the charac¬ 
teristics of the primitive state. 
§ 57. Similar experiments with other specimens of wire, and at other points in 
the curve of magnetisation, gave results confirmatory, in every particular, of the 
above. When the magnetisation is strong, however, the differences produced by 
repetitions of the same process are insignificantly small: and it is in the early parts of 
the curve that we find the most striking effects. One or two other examples may be 
given very briefly. 
Soft iron wire, freshly annealed. 
Magnetising Current. 
Magnetometer. 
Gradually .... 
100 
+ 130 
-100 
-125 
33 .... 
+ 100 
+ 117 
-100 
-116 
Suddenly .... 
+ 100 
+ 109 
1 Here the repetition of the reversal, although 
33 .... 
-100 
-114 
J sudden, still causes diminution of range. 
Fifty more double reversals, 
then—• 
Suddenly .... 
+ 100 
+ 106 
-100 
-106 
Gradually .... 
+ 100 
-100 
+ 103 
-104 
j Here even after many sudden reversals a gradual 
> reversal still causes a decided lessening of the 
J range. 
