rise during the first years succeeding the invention of
the telephone to a considerable number of investigations, the principal
results of which may be summed up in the two following points:

1. All the parts of a telephone receiver--core, helix, disk, handle,
etc.--vibrate simultaneously (Boudet, Laborde, Breguet, Ader, Du Moncel,
and others). But there is no doubt that by far the most energetic effects
are those of the disk. It has been possible to put the vibrations of the
core and helix beyond a doubt only by employing very energetic
transmitter currents, or very simplified and special arrangements of the
receiver (Ader, Du Moncel, and others).

2. In telephone receivers we may employ disks or diaphragms of any
thickness up to six inches (Bell, Breguet, and others).

From the first point it had already resulted that the diaphragm was no
more indispensable in the receiver than it was in the transmitter, as I
have already shown (_Comptes Rendus_, t. ci., p. 944); and, from the
second point, that there were other effects in a receiver than those that
could result from the transverse vibrations corresponding to the
fundamental sound and to the harmonics of the diaphragm.

So Du Moncel, basing a theory upon these two categories of facts,
asserted that the effects of the telephone receiver were principally due
to the molecular vibrations of the core of the electro-magnet (analogous
to those that had been studied by Page, De la Rive, Wetheim, Reis, and
others), super-excited and re-enforced by the iron diaphragm operating as
an armature.

This theory has certainly truth for a basis; but it is incomplete, in
that the molecular vibrations of the core are but a very feeble accessory
phenomenon, and not a prominent one. At all events, I believe that we
can, in a few words, and very simply, present the theory of the telephone
receiver by going back to the facts that served me as a basis for the
theory of the transmitter, and that result from studies made with
telephones of ordinary forms.

In fact, it is enough to remark that the iron filings telephone
transmitter described in a preceding article (_1. c_.) is reversible and
capable of serving as a receiver--not a very intense one, it is true, but
here it is a question of the _nature_ of the phenomena, and not of their
intensity. It at once results that in receivers, as in transmitters, the
rigidity of the iron diaphragm is in nowise indispensable for telephonic
effects, s