Later Van Rysselberghe changed these
arrangements for the still simpler device of introducing permanently
into the circuit either condensers or else electro-magnets having a
high coefficient of self-induction. These, as is well known to all
telegraphic engineers, retard the rise or fall of an electric current;
they fulfill the conditions required for the working of Van
Rysselberghe's method better than any other device.
Having got thus far in his devices for destroying induction from one
line to another, Van Rysselberghe saw that, as an immediate
consequence, it might be concluded that, if the telegraph currents
were thus modified and graduated so that they produced no induction in
a neighboring telephone line, they would produce no sound in the
telephone if that instrument were itself joined up in the telegraph
line. And such was found to be case. Why this is so will be more
readily comprehended if it be remembered that a telephone is sensitive
to the changes in the strength of the current if those changes occur
with a frequency of some hundreds or in some cases thousands of times
_per second_.
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