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 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).