639 
may be repeated 5 or more times. When bv stretching the remanent 
magnetism has been destroyed, further stretching does not recall the 
sound. Exactly the same phenomenon is observed during small torsions 
after magnetisation of the wire and also during a short heating of 
the wire e. g. by touching the wire with a Bunsen-flame, each time 
during part of a second. The sound heard during stretching, torsion 
or heating has quite the same character as that observed during the 
magnetisation. We therefore conclude: the destruction of the remanent 
magnetism in soft-iron by stretching, torsion or heating gives rise to 
discontinuities analogous to those occurring during the magnetisation 
or demagnetisation. 
A strong circular magnetisation causes a superponed magnetisation- 
in longitudinal direction of the rod to take place without disconti- 
nuities. For the above mentioned 1 mm. thick soft-iron wire a current 
of 7 Amp. had to be sent through it to produce the circular mag- 
netisation before the sound vanished. During such an experiment the 
temperature of the wire is of course considerably higher and one 
might feel inclined to ascribe the failing of the discontinuities to 
the rise of temperature. However, immediately after the closing 
of the current of 7 Amp. the sound vanishes in the case of longi- 
tudinal magnetisation and immediately after the breaking of the 
current it reappeared. In both cases the change of temperature must 
be still small. These experiments therefore prove that it is the circular 
magnetisation that prevents the discontinuities in the longitudinal 
magnetisation taking place. 
An annealed iron wire shows further by this sensitive method of 
observation the following remarkable property. When the iron has 
received its remanent magnetism in the above described way, this 
may be destroyed under the characteristic iron sounds by bending 
the part of the rod within the solenoid alternately to the right and 
to the left. But when afterwards this bending is continued the 
characteristic sound remains audible though somewhat weaker. Also 
a freshly annealed wire that has not been magnetised before, shows 
this last phenomenon. This bending may be repeated indefinitely, 
always the sound is heard with the same intensity. Tbis experiment 
seems to be a proof for the theory of Weiss on the spontaneous 
magnetisation of iron crystals. We may not consider the phenomenon 
to be due to the presence of the terrestrial field; for a weak direct 
current through the solenoid compensating or increasing the field in 
the coil has no influence whatever. We might formulate an explanation 
in the following way: by the bending the mutual positions of the 
spontaneously magnetised crystals are changed and by reversing 
41* 
