COMMON COMMODITIES AND INDUSTRIES "LITTLE GEEKO" DIRECT WORKING TELEPHONES For operating on existing bell circuits in Shops, Offices, Warehouses, Factories, Private Houses, etc. Easily installed. Efficient in working. G.E.C. Telephones have many years of unequalled reputation behind them and can be recommended with the utmost confi- dence. Sound construction, com- bined with expert workmanship, and the use ol iho finest materi als , has resulted in the pro- duction of instru- ments of first class quality. Full particulars and expert advice can always be obtained K7765 on application. The GENERAL ELECTRIC CO., LTD. Principal Showrooms and Sales Depot 67 Queen Victoria Street, London, E.C.4 Branches throughout the United, Kingdom K7730 YOUR ORGANISATION |TT ^jj is incomplete without THE RELAY AUTOMATIC TELEPHONE SYSTEM, which is entirely AUTO- MATIC and requires NO OPERATORS. In four seconds you are either connected and can speak to the desired number, or in- formed by a low buzzing sound in the receiver that the line is engaged. Call and see the system demonstrated or write to-day for an illustrated booklet. The Relay Automatic Telephone Co., Ltd. .5S4=&/^ Marconi House Strand, London W.C.2 Telephone City 281 AUTOMATIC INTERPHONES THE present-day perfection of STERLING TELE- PHONES is the direct result of twenty years practical experience in the manufacture of Telephones for The STERLING " " every purpose. PRIMAX SYSTEM is unequalled for simplicity and efficiency. Selecting and ringing are per- formed at one operation there are no buttons to push. Made throughout at the STERLING WORKS, DAGENHAM, Essex, by skilled British labour using the best obtainable material. Write for latest lists STERLING TELEPHONE & ELECTRIC Co. Ltd. 210-212 Tottenham Court Road, London, W.I Telegrams " Telephone Cucumis, Ox, London." Nos. 4144 Museum (7 Lines). 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THE INDUSTRY. By B. W. POOLE, M.U.K.A. THE BOOT AND SHOE INDUSTRY. TELEGRAPHY, TELEPHONY, AND By J. S. HARDING WIRELESS. By J. POOLE, GAS AND GAS MAKING. By A.M.I. E.E. W. H. Y. WEBBER PERFUMERY. By E. J. PARRY. FURNITURE. H. E. BINSTEAD By THE ELECTRIC LAMP INDUSTRY. COAL TAR. By A. R. WARNES By G. ARNCLIFFE PERCIVAL. PETROLEUM. A. LIDGETT By ICE AND COLD STORAGE. By B. H. SALT. By A. F. CALVERT SPRINGETT. OTHERS IN PREPARATION P PITMAN'S COMMON COMMODITIES AND INDUSTRIES SERIES TELEGRAPHY, TELEPHONY AND WIRELESS J. POOLE, WH.SCH., A.M.I. E.E. AUTHOR OF " THE PRACTICAL TELEPHONE HANDBOOK " LONDON SIR ISAAC PITMAN & SONS, LTD. PARKER STREET, KINGSWAY, W.C.2 BATH, MELBOURNE, TORONTO, NEW YORK PRINTED BY SIR ISAAC PITMAN & SONS, LTD. BATH, ENGLAND PREFACE THIS book is intended as a short general introduction to the three industries, or vocations, dealing with the electrical transmission of intelligence, which have now assumed such very great importance in the intercourse between the peoples of all civilized nations. They are all really different branches of the oldest of them, which was born about 1834 telegraphy, commercially ; the telephone industry commencing about forty-five " " years later, in 1878-9, and that of wireless in 1904, when an arrangement was made by which the British Post Offices received messages for transmission by Marconi wireless stations. The historical method has been used, as it was con- sidered best adapted to impress the principles of working on readers new to the subjects dealt with, by leading up from the simpler to the more complex apparatus. A somewhat larger share of space in the book has been given to the wireless than to the other two sections, as it, no doubt, attracts more general interest at the present time, but it is believed that no important feature of the other two sections has been neglected. The writer is indebted to the following books for borrowed illustrations, viz., Herbert's Telegraphy, 3rd edition, Pendry's Elementary Telegraphy," 2nd edition, Merchant's Wireless Telegraphy, 2nd edition, and to Mr. T. Sherratt, A.M.I. E.E., for kindly correcting the proofs. J. POOLE & Co. 104 Charing Cross Rd., W.C.2 ESTABLISHED 1854 ALWAYS A LARGE STOCK OF EDUCATIONAL AND TECHNICAL BOOKS All enquiries answered. Orders by post receive immediate attention BOOKS SCIENTIFIC-ELECTRICAL-ENGINEERING 1,000,000 Volumes in stock on OVERevery conceivable subject in strictly classified order. Second-hand and New. Books sent on approval. We have the books you want. There are always Bargains on our shelves. Catalogue No. 273 free. State wants. Books bought ; best prices given. W. & G. FOYLE, LTD. CONTENTS CHAP. PAGE PREFACE ...... V I. INTRODUCTORY 1 II. SOURCES OF ELECTROMOTIVE FORCE ; ELEC- TRIC BELLS AND RELAYS ... 13 III. TELEGRAPHY 26 IV. TELEPHONY 51 V. TELEGRAPH AND TELEPHONE LINES . 81 ^ VI. WIRELESS TELEGRAPHY . 89 VII. WIRELESS TELEPHONY . .113 INDEX 118 TELEGRAPHY, TELEPHONY AND WIRELESS CHAPTER I INTRODUCTORY IN order to render the subject matters treated of in this book clear to the general reader a few introductory remarks and definitions are considered desirable as to the .nature or effects of the imponderable something which we call electricity. Frictional Electricity. The first recorded fact in connection with it was that if the substance amber was rubbed by the hand or a cloth, it would attract very light bodies to its surface and in the dark give off sparks. These facts were known in the very early ages, and it was not until the beginning of the seventeenth century that Dr. William Gilbert 'found that many " " other substances also became electrified when rubbed. He also found that there were two kinds of " " electricity which were always produced together, one kind on the rubbed and the other kind on the rubber, and that bodies electrified with the same kind repelled " " each other and bodies electrified or charged with different or opposite kinds . attracted each other. Conductors and Insulators. Some of the substances thus electrified were found to lose their charges very rapidly when touched and others retained their charges after the former were called conductors being touched ; and the latter insulators, but there is infinite variety TELEGRAPHY, TELEPHONY AND WIRELESS in the various substances in regard to these properties of conductivity and insulation. In order to retain a charge of electricity on a good conducting body, such as a metal, it is necessary to support it by means of a good non-conducting or insulating body, such as indiarubber or such like but glass, porcelain, silk, ; unless the air surrounding the conductor is also dry even the insulators will not succeed in retaining the charge. The insulators are, therefore, said to have a high or great resistivity to the passage of electricity and the conductors offer small resistance to the escape or passage of the electricity. Potential. Bodies may be feebly or powerfully charged with electricity and the intensity of such " charge is called its potential," which is measured by units called volts. Potential is analogous to head of water in connection with a turbine, or pressure of steam in a steam engine boiler and is a gauge of the intensity of the effects it can produce. Electrical Current. When two points in a conducting body become charged with electricity at different potentials a current of electricity is caused to pass through the conductor. This current may be only momentary if there is nothing to maintain the difference between the potentials of the two points, or it will be a " " continuous one if such points can be maintained at " " " a difference of potential or P.D," by some source " a of electro-motive-force, such as a battery or " dynamo machine." These will be described later.