981 
and is 343 millimetres long. Figure 2 shows the hysteresis curve ot 
a soft iron wire (diametre 1.82 millimetres, length 349 millimetres). 
Fig. 2. 
In order to obtain (for the determination of the part where the 
discontinuities occur) a very gradual increase of the magnetising 
current, two copper plates in series with the magnetising solenoid 
were placed next to each other in a glass jar. With the aid of a 
siphon arrangement this jar was gradually filled with a copper- 
sulphate solution, which caused a decrease of the resistance and a 
rather continuous increase of the current through it. After the Ni Fe 
or Fe wire was put in the magnetising solenoid together with a 
second induction solenoid closely surrounding the wire, we determined 
with the aid of a telephone connected to the induction solenoid 
through a three stage triode amplifier, the point on the hysteresis 
curve where the discontinuities for the first time occur and the spot 
where they disappear again. 
It appeared that the discontinuities in the magnetic induction only 
occur on the steep parts of the hysteresis curves, viz. in figure 1 
and 2 on the parts A—S and C—D. The part from saturation to 
where =O, and where therefore only the remanent magnetisation 
is left, is, at any rate as far as can be observed, quite continuous. 
However, as soon as H changes its sign and therefore the existing 
magnetisation is reduced, the discontinuities begin to occur. They 
are further audible over a certain distance, which however does not 
reach quite to saturation. The rustling noise in the telephones, as 
64 
Proceedings Royal Acad. Amsterdam. Vol. XXIII. 
