For several years my attention was almost exclusively directed to the production of an instrument for making and breaking a voltaic circuit with extreme rapidity, to take the place of the transmitting tuning-fork used in Helmholtz’ researches. I will not trouble you with the description of all the various forms of apparatus that were devised, but will merely direct your attention to one of the best of them, shown in fig. 2. In the transmitting instrument T, a steel reed _a_ is employed, which is kept in continuous vibration by the action of an electro-magnet _e_ and local battery. In the course of its vibration the reed strikes alternately against two fixed points _m_, _l_, and thus completes alternately a local and a main circuit. When the key K is depressed an intermittent current from the main battery B is directed to the line-wire W, and passes through the electro-magnet E of a receiving instrument R at the distant end of the circuit, and thence to the ground G. The steel reed A is placed in front of the receiving magnet, and when its normal rate of vibration is the same as the reed of the transmitting instrument it is thrown into powerful vibration, emitting a musical tone of a similar pitch to that produced by the reed of the transmitting instrument, but if it is normally of a different pitch it remains silent. [Illustration: Fig. 2.] [Illustration: Fig. 3. Fig. 4. Fig. 5.] A glance at figs. 3, 4, and 5 will show the arrangement of such instruments upon a telegraphic circuit, designed to enable a number of telegraphic despatches to be transmitted simultaneously along the same wire. The transmitters and receivers that are numbered alike have the same pitch or rate of vibration. Thus the reed of T´ is in unison with the reeds T´ and R´ at all the stations upon the circuit, so that a telegraphic despatch sent by the manipulation of the key K´ at the station shown in fig. 3 will be received upon the receiving instruments K´ at all the other stations upon the circuit. Without going into details, I shall merely say that the great defects of this plan of multiple telegraphy were found to consist, firstly, in the fact that the receiving operators were required to possess a good musical ear in order to discriminate the signals; and secondly, that the signals could only pass in one direction along the line (so that two wires would be necessary in order to complete communication in both directions). The first objection was got over by employing the device which I term a “vibratory circuit-breaker,” shown in the next diagram, whereby musical signals can be automatically recorded. [Illustration: Fig. 6.]