983 
continuously. By using this arrangement the magnetising current 
could in one minute very gradually be increased e.g. from 0.200 
Amp. to 0.230 Amp. 
The discontinuities which occur in the magnetic induction in the 
NiFe wire, the magnetic field being controlled by the thermal 
method, are shown in fig. 4, which gives two photographic reproductions 
on the same plate of the deflection of an ordinary StemeNs and HALSsKE 
moving coil galvanometer. This galvanometer was connected (without 
series resistance or triode amplifier) to a long secondary coil of 
16500 turns (566 Ohm), which narrowly surrounded the NiFe wire 
over its total length. In 6 seconds the field increased from 6.0 to 
6.2 Gauss, it having been brought before a few times alternately 
to + 36 Gauss. As the galvanometer was very damped, we can 
consider the curves of fig. 4 to approximately represent a small 
part of the hysteresis curve. (See appendix). The discontinuities in 
the induction are very well visible; the upper curve e.g. shows 6 
sudden increases of the 5. 
Obviously the biggest discontinuities only are registered by a 
moving coil galvanometer. However, the phenomenon can be followed 
more in detail by using an EiNTHoveN string galvanometer. Various 
photograms directly on bromide paper were obtained by using the 
latter galvanometer, the bromide paper having been mounted on a 
revolving cylinder, every point of which described a screw curve 
with a pitch of 1 centimetre. 
Figures 5 and 6 are parts of larger photograms. Figure 5 is 
obtained with the above mentioned nickelsteel wire and figure 6 
with a soft iron wire. In both cases the 566 ohm induction solenoid 
surrounded the ferromagneticum over its total length, and in both 
cases the sensitivity of the galvanometer was the same, viz. such, 
that a deflection of 1,0 centimetre (the distances between the sub- 
sequent pitches) corresponds to 0,18.10-° Amp. The width of either 
photogram corresponds to one second. The photos were taken after 
(in both cases) the material was brought on the steep part of the 
hysteresis curve, where the discontinuities are most frequent. The 
continuous increase of the field was obtained with the thermal current 
control of fig. 3 such, that the field, when using nickelsteel, increased 
in 37 seconds from 6.0 to 6.7 Gauss and, when using iron, in 60 
seconds from 4,8 to 5,5 Gauss. In the photograms the time runs 
from left to right aud the bottom part was described first. The time 
in which the string reaches its new equilibrium position when a 
constant current is made and broken, is shown at the bottom of 
the photograms. 
64* 
