another room or in another house, with the receiver at his ear, might hear exactly what those did who were in the same room with the buzzers. The wires from the receiver were connected with the coil in each buzzer so as to get the induced current, as shown in detail in Fig. 160. [Illustration: Fig. 160] [Illustration: Fig. 161] [Illustration: Fig. 162] We took a telephone induction coil (Fig. 162) and fastened it to a board as represented in Fig. 163, _I_. One wire of the primary circuit was fastened to the binding post _a_. The other wire from the primary coil passed to the switch _S_ and then to the battery. From the battery the wire ran to the binding post _b_. _C_ is a steel tuning fork. The secondary circuit is closed through a telephone receiver. These wires are extended so that the receiver is too far distant for the tuning fork to be heard through the air. When the switch _S_ is closed the tuning fork acts as the interrupter for the primary circuit, and it interrupts according to its time of vibration. If, for instance, the fork gives the tone of middle _C_ on the piano it vibrates 256 times a second. It interrupts the primary circuit 256 times a second. It induces an alternating current of the same frequency in the secondary circuit. The diaphragm of the telephone receiver vibrates in perfect time with the tuning fork and produces the same tone as the tuning fork. We had a series of tuning forks giving a variety of tones, which we could substitute one after another in place of this one. The receiver reproduced accurately the tone of each one of them. [Illustration: Fig. 163] [Illustration: Fig. 164] We took a small induction coil (Fig. 164) _c_ and fastened one end of the primary circuit to a battery, _B_. The wire at the other end of the primary circuit was bent into a hook _h_. This hook was adjusted about a quarter of an inch from the end of the iron core of the coil. The other wire from the battery was attached to the steel strings of a piano, _P_. When the coil _c_ was brought over a string and the hook _h_ was allowed to pass beneath the string and touch it very gently, the primary circuit was closed through the string, which served as an interrupter of the current and vibrated according to its tone. The secondary coil, not represented in the figure, was connected to a distant telephone receiver, which reproduced the tones of the piano strings.