119.—Details of the Magnet Spools, and Yoke for an Electric Bell. ............................................................. Fig. 120.—Details of the Armature, and Contact Screw. ............. Fig. 121.—The Completed Bell. ..................................... Fig. 122.—Diagram showing how to connect a Bell, Battery, and Push-Button. ...................................................... Fig. 123.—Two Simple Push-Buttons. ................................ Fig. 124.—Diagram showing how to arrange a Bell System of Return Signals. .......................................................... Fig. 125.—Burglar-Alarm Trap. ..................................... Fig. 126.—An Early-Riser’s Electric Alarm Attachment for a Clock. . Fig. 127.—Details of the Chain Electrodes, etc. ................... Fig. 128.—An Annunciator Drop. .................................... Fig 129.—Details of the Drop-Frame and Armature. .................. Fig. 130.—A Typical Telegraph Key, showing the Various Parts. ..... Fig. 131.—A Typical Telegraph Sounder, showing the Various Parts. . Fig. 132.—A Simple Home-made Telegraph Key. ....................... Fig. 133.—A Simple Home-made Telegraph Sounder. ................... Fig. 134.—A Diagram showing how to connect two Simple Telegraph Stations. ......................................................... Fig. 135.—A Complete Telegraph Set, consisting of a Keyboard and a Sounder. .......................................................... Fig. 136.—Details of the Telegraph Set shown in Figure 135. ....... Fig. 137.—A Diagram showing how to connect two Complete Telegraph Sets, using one Line Wire and a Ground. The Two-Point Switches throw the Batteries out of Circuit when the Line is not in use. ......... Fig. 138.—Details of the Relay Parts. ............................. Fig. 139.—The Completed Relay. .................................... Fig. 140.—A Diagram showing how to connect a Relay, Sounder, and Key. Closing the Key will operate the Relay. The Relay will then operate the Sounder in turn. ...................................... Fig. 141.—How to hold a Telegraph Key. ............................ Fig. 142.—The Morse Telegraphic Code. ............................. Fig. 143.—A Microphone connected to a Telephone Receiver, and a Battery. .......................................................... Fig. 144.—A Very Sensitive Form of Microphone, with which the Footsteps of a Fly can be heard. .................................. Fig. 145.—A Telephone System, consisting of a Receiver, Transmitter, and a Battery connected in Series. Words spoken into the Transmitter are reproduced by the Receiver. ................................... Fig. 146.—A Watch-Case Telephone Receiver. ........................ Fig. 147.—A Simple Form of Telephone Receiver. .................... Fig.