| LIST OF PLATES |
| I | One of the Lines of Towers at Radio Central | Frontispiece |
| II | Bird’s-Eye View of Radio Central | 10 |
| III | Dry Battery for Use in Audion Circuits, and also Storage Battery | 27 |
| IV | Radiotron | 42 |
| V | Variometer and Variable Condenser of the General Radio Company. Voltmeter and Ammeter of the Weston Instrument Company | 91 |
| VI | Low-Power Transmitting Tube, U V 202 | 106 |
| VII | Photographs of Vibrating Strings | 155 |
| VIII | To Illustrate the Mechanism for the Production of the Human Voice | 170 |
| IX | Western Electric Loud Speaking Receiver. Crystal Detector Set of the General Electric Co. Audibility Meter of General Radio Co. | 203 |
| X | Audio-Frequency Transformer and Banked-Wound Coil | 218 |
| XI | Broadcasting Equipment, Developed by the American Telephone and Telegraph Company and the Western Electric Company | 235 |
| XII | Broadcasting Station of the American Telephone and Telegraph Company on the Roof of the Walker-Lispenard Bldg. in New York City where the Long-distance Telephone Lines Terminate | 250 |
