984 
The considerable difference between the discontinuities in the iron 
and nickelsteel is very well marked in these figures. When using 
nickelsteel the clapses are much stronger; the photograms therefore 
confirm the observations made before with triode amplifier and 
telephone. Apart from giving the intensity, the photograms also enable 
us to count approximately the number of discontinuities. 
Thus for nickelsteel 1554 clapses were found for a change of 
field from 6.0 to 6.7 Gauss, and for iron 1546 clapses for a change 
of field from 4.8 to 5.5 Gauss. Moreover the region on the hyste- 
resis curve where the discontinuities occur (see fig. 1 and 2) being 
known, as well as the fact that the number of clapses at A and C 
in the figures mentioned does not reach its maximum value at 
once, we can approximately estimate the number of clapses during 
a complete reversal of the magnesitation. Thus we found: 
for nickelsteel wire (dia. 1.98 mm., length 343 mm.) 5000 clapses, 
soft iron wire (dia. 1,82 mm., length 349 mm.) 6500 clapses. 
We did not examine more in detail the dependency of the number 
of discontinuities upon the diameter and the length of the ferro- 
magnetic wire. One should be inclined to expect this number to be 
proportional to the volume or, if long iron filaments are magnetised 
as a whole, to the diameter; but on the other hand eddy currents 
will occur in the outer layers, if an ironerystal in the inner part 
is suddenly remagnetised, which eddy currents may be expected to 
reduce the suddenness of the currents in the induction solenoid, and 
also the rustling noise in the telephone receiver. Very likely, owing 
to these eddy currents, jumps of most different values appear on the 
photograms, though possibly one definite intensity of magnetic moment 
of the crystal is prevalent. 
Finally, the assumption that, under certain circumstances, the mag- 
netic moments of long filaments suddenly" change as a whole (see 
Le.) was found confirmed by the following experiment. 
The nickelsteel wire was brought into the magnetising solenoid, 
and the current was controlled thermally in the way described 
above. The nickelsteel core was surrounded by two small flat coils 
of 3 mm. axial length, on either of these coils 2600 turns of ena- 
melled copper wire of 0,05 mm. had been wound (the inner dia- 
meter of the coil being 3,4 mm., the outer one 13.0 mm.). The 
distance between the two coils could be given any arbitrary value. 
Hither coil was connected to one of two identical moving coil 
galvanometers. Both the galvanometer spots had the form of a line 
inclined at 45° to the horizon. They were projected on the same 
scale and formed together a cross. |X| 
