PREFACE TO THE FIRST EDITION. This book was written at the suggestion of the publisher, Dr. Enke. It was originally intended to be an abridged form of my larger book Elektrornagnetische Schwingungen und drahtlose Telegraphie Stuttgart, 1905. It has, however, developed into something quite different - evidence of this lies in the fact that only 79 of the 332 illustrations of the larger book have been reproduced here. Since I began writing this book winter 1905-1906 conditions in wireless telegraphy have changed greatly. The mere fact that new devices and methods have appeared would be of relatively little importance but the points of view determining the consideration of many of the problems of the art have changed entirely. This necessitated rewriting many portions of the book, which would otherwise have been out of date from its very publication. I need hardly dwell on what this has meant for both the publisher and myself. The mathematical premises are the same as in my larger book. In the text, knowledge of only elementary mathematics-the use of differential and integral calculus would have offered no advantage,-in the Notes, knowledge of the electromagnetic theory is assumed. The physical premises are somewhat higher than in the larger book knowledge of experimental electro-physics and of the phenomena of alternating currents, in short the ground covered by the first four chapters of my larger book, is necessary for a thorough understanding of this volume. I have been somewhat more sparing with the bibliography, for since a year ago, Dr. G. Eichhorn, in the Jahrbuch fiir drahtlose Telegraphie, gives detailed references to the literature on the subject. As regards the commercial form of the apparatus, most frequent reference has been made to the German manufacturers Ges. f. drahtl. Tel. and Amalgamated Radio-telegraph Co., i. e., C. Lorenz, A. G.. In so doing I had no desire to show these firms any preference. Description of all the different makes of apparatus would have been prohibitive, and I have simply chosen as examples the apparatus of those firms which placed exact data and photographs at my disposal. Moreover other makes of apparatus are fully described in other books I might mention the excellent works of J. A. Fleming and particularly of J. Erskine-Murray in this connection. J. ZENNECK. BRAUNSCHWE P I H G Y , S IKALISCHES INSTITUT DEB TECHNISCHEN HOCHSCHULE, - Dez., 1908. AUTHORS PREFACE TO THE SECOND EDITION Only two and a half years after the appearance of the first edition, a second one has become necessary, even though a French edition had already appeared in the mcantime. The book, therefore, has been accorded a much more favorable reception than I had dared hope. This served particularly to spur me on to do everything within my polvcr to make the second edition representative of the present status of vireless telegraphy...