570 
PROFESSOR J. A. EWING ON EXPERIMENTAL 
such as they are, are of the kind which Yon Waltenhofen’s experiments would lead 
us to expect, but their magnitude is not such as to make results got by the ballistic 
method be materially different from results got by the magnetometric method. 
In the following experiments the comparative effects of slow and sudden 
changes of magnetising force are involved, along with certain other phenomena which 
will now be described, and which are in part a mere confirmation of results already 
published by C. FrommeA 
§ 54. Effects of Repeated Application and Removal of Magnetising Force .— 
When a magnetising force is first applied, then removed, and then re-applied, whether 
suddenly or gradually, the resulting value of 3 is somewhat higher than that reached 
by the first application. A third application gives a somewhat higher value, and so 
on, the effects apparently approaching an asympotic limit. This has been already 
shown by the experiments of Fromme. At each removal of the magnetising force 
the residual magnetism is also left somewhat greater than before. And this second 
action (the increase of the residual magnetism) exceeds the increase of the induced 
magnetism, with the result that the changes of magnetism between residual and 
induced diminish in range with successive removals and re-applications of the 
magnetising force. 
The following observations were made by the ballistic method on a long piece of 
soft annealed iron wire. The readings are given without reduction to absolute 
measure ; they relate to a point which falls early in the steep part of the curve of 
magnetisation. 
Magnetising Current. 
Throw of Ballistic 
Galvanometer- 
Magnetism. 
First made. 
203 
203 
broken , . 
-53-6 
149-4 
made. 
+ 54-2 
203-6 
broken . . 
-47'8 
155-8 
made ........ 
+ 48-7 
204-5 
broken . 
-45-7 
158-8 
made. 
-f-46'6 
205-4 
broken . 
-44-9 
160-5 
made. 
+ 46-1 
206-6 
broken . 
-44-0 
162-6 
made. 
+ 45-6 
208-2 
After many makes and breaks— 
broken.. 
-42-6 
made. 
+ 43-1 
After many more makes and breaks—• 
broken . 
-39-5 
made. 
+ 39-8 
Similar results were repeatedly obtained, both with freshly aimealed wires and wires 
from which a previous strong magnetism had been shaken out by tapping. In curves 
* Pogg. Ann., Ergbd. vii., 1875, and Wied. Ann., iv., 1878. 
