[Illustration:  DR. HERZ’S TELEPHONIC SYSTEMS.]

This arrangement evidently presented its advantages; but it likewise possessed its inconveniences, one of the most important of these being the necessity of employing rather strong piles and consequently of exposing the line to those effects of charge which react in so troublesome a manner in electrical transmissions when they occur on somewhat lengthy lines.  Now the fact should be recalled that Dr. Herz’s principal object was the application of the telephone to long lines, and he has been applying himself to this problem ever since.  He at first thought of employing reversed currents, as in telegraphy; but how was such a result to be attained with systems based upon the use of sonorously-vibrating transmitters?  He might have been able to solve the problem with the secondary currents of an induction bobbin, as Messrs. Gray, Edison, and others had done; but then he would no longer have been benefited by those amplifications which are furnished by the variations of pressure-derivations in microphones, and this led him to endeavor to increase the effects of the induced currents themselves by prolonging their duration, or rather by combining them in such a way that they should succeed each other, two by two, in the same direction; and this is the way he solved the problem in the beginning.

The fact should also be recalled that Dr. Herz had, from his first experiments, recognized the efficiency of those microphonic contacts that are obtained by the superposition of carbon disks or other semi-conducting substances.  He has employed these under different arrangements and with very diverse groupings, but, as a general thing, it has been the horizontal arrangement which has given him the best effects.

Let us suppose, then, that four systems of contacts of this nature are arranged at the four corners of an ebonite plate, C C (Figs. 1 and 2), at A, A¹, B, B¹, and that they are connected with each other, as shown in the cuts—­that is to say, the upper disks, e, f, g, h, parallel with the sides of the plate, and the lower disks, A, A¹, B, B¹, diagonally.  Let us admit, further, that the plate pivots about an axis, R; that the disks are traversed by small pins fixed in the plate; and that small leaden disks rest upon the upper disks.  Finally, let us imagine that the plate is connected at one end, through a rod T, with a telephone diaphragm.  Now it will be readily understood that the vibrations produced by the diaphragm will cause the oscillation of the plate, C C, and that there will result therefrom, on the part of the disks, two effects that will succeed one another.  The first will be, for the ascending vibrations, an increase of pressure effected between the disks of the left side, by reason of their force of inertia being increased by that of the lead disks; and the second will be, for the disks to the right, and, for the same reason, a reduction of pressure which will take place through resilience, at the moment of change in direction of the vibrating motions.