t clearly
demonstrates.

II. Let us now pass to the _magnetic role_ of the telephone diaphragm.
Such _role_ can be clearly enough defined by the following facts:

(1.) The presence of the magnetic field of the telephone in nowise
changes the preceding conclusions.

(2.) Upon farther and farther diminishing the stiffness and elasticity of
the diaphragm, I have succeeded in suppressing it entirely. In fact, it
is only necessary to substitute for it, in any telephone whatever, a few
grains of iron filings, thrown upon the pole of the magnet, covered with
a bit of paper or cardboard, in order to render it possible to reproduce
all sounds, and articulate speech with its characteristic quality,
although, it is true, with very feeble intensity.

(3.) In order to increase the intensity of the effect produced, it
suffices to substitute for the iron diaphragm a thin disk of any sort of
slightly flexible substance, metallic or otherwise, cardboard, for
example, and through the aperture of the usual cover of the instrument to
scatter over it from 11/2 to 3 grains of iron filings. In this way we
obtain an iron filings telephone. By properly increasing the intensity of
the magnetic field, I have been able to form telephones of this kind that
produced in an ordinary receiver as intense effects as those given by
the usual transmitters with stiff disks, and which, too, were reversible.
But for a field of given intensity, there is a weight of iron filings
that produces a maximum of effect.

We thus see that the advantage of the iron diaphragm over filings is
truly reduced to the presentation of a much larger number of magnetic
molecules to the action of the field and to external actions, within the
same volume. It increases the _intensity_ of the telephonic effects,
although for _the production_ of the latter with all their variety,
fineness, and perfection it is nowise indispensable. It suffices, after a
manner, to materialize the lines of force with iron filings, and to act
mechanically upon them, and consequently upon the field itself.

* * * * *

ON THE THEORY OF THE RECEIVER OF THE ELECTRO-MAGNETIC TELEPHONE.

By E. MERCADIER.

[Footnote: Note presented to the Academy of Sciences, November 16, 1885.]

On a former occasion I described some experiments that had led me to a
theory of the telephone transmitter; a few words will suffice to expose
that of the receiver.

Such theory gave