708 
Proceedings of the Royal Society 
2. It was found, however, that when the secondary circuit was 
broken, loud sounds were emitted at the pools of the mercury break. 
These sounds appear to he due to electrostatic action. They are 
most probably of the same nature as those obtained in Thomson’s 
singing condenser, Edison’s condenser telephone, &c. 
3. If the wire of the wire telephone he placed across the lines of 
force in a strong magnetic field, very loud and pure sounds are ob- 
tained when a current interrupted by a tuning-fork is passed through 
it. These sounds can he obtained with very thick wires of any 
metal. If a tolerably thin wire he used, although the sound is not 
much louder, the amplitude of the vibration increases ; as much as 
2 mm. was observed. 
4. Experiments were also made with a view to explain the 
anomalous behaviour of iron wires established by De la Eive and 
Dr Ferguson. 
Experiments with soft iron wires showed that the sounds did not, 
in the case of iron, depend in the same way on the length and 
thickness as they do in the case of ordinary metals, and that their 
quality is essentially different. The note of the interruptor is often 
not heard at all, but instead, a variety of other notes are produced, 
some of them very high accompanied with a fizzing or buzzing noise. 
The sound depends on the temperature of the wire, being loudest 
about a dull red heat, just above the temperature at which the 
abnormal extension and contraction and the re-glow are usually ob- 
served. At higher temperatures the sound falls off very rapidly. 
These results suggested that the sound is a consequence of the 
magnetism of the iron ; for, in the case of soft iron, the magnetic 
susceptibility is at a maximum about the temperature above men- 
tioned, and falls off very rapidly at higher temperatures. 
Experiments with steel wires settled the question, for it was 
found that when the steel was made white hot and then tempered, 
so as to deprive it of its permanent magnetism and make it hard, it 
gave no sound at all in the wire telephone. On magnetising it, 
however, by stroking once or twice with a bar magnet, it sounded 
quite distinctly, giving a high note and a soft fizzing sound. 
The effect of heating a magnetised steel wire is as follows : — At 
first the sound falls off, first the fizzing disappears, then the high 
note ; then comes an interval of silence j then, ‘as the temperature 
