LIBRARY OF THE UNIVERSITY OF CALIFORNIA. Class : ; I ^BTHERIC OR WIRELESS TELEGRAPHY. jETHERIC OR WIRELESS TELEGRAPHY. BY ROBERT GORDON ELAINE, M.E., rl ASSOC.M.INST.C.E., ETC., Lecturer at the City and Guilds of London Technical College^ Finslury. " "Lessons on Practical <>f "Hydraulic Machinery t Mechanics,' "The Slide Rule," etc. LONDON : BIGGS AND SONS, 139-140, SALISBURY GOURT, E.G. PUBLISHERS' PREFACE. Experiments in wireless telegraphy are by no means new, but previous to the discovery of the telephone they consisted entirely of making earth or water, or both combined, part of a telegraphic circuit. Bell's discovery led to experiments which proved that the telephone could be acted upon at a distance inductively, but there was no commercial practicability in the various schemes devised. The development of knowledge relating to Hertzian waves really led us to what the moderns term wireless telegraphy. This little book deals, almost exclusively with these later developments. 224520 CONTENTS. PAGE. INTRODUCTION ... ... ... ... ... 9-15 CHAPTER I. FUNDAMENTAL FACTS AND NOTIONS 16-31 The Ether 20 What is Electricity ? The Electronic Answer ... ... ... ... ... 24 CHAPTER II. TELEGRAPHY ... 3 2 --M Methods of Signalling" ... ... ... 39 CHAPTER III. EARTH CONDUCTION SYSTEMS ... ... ... 42-68 Induction Systems ... ... ... ... 52 Hertz-Wave Systems ... 60 CHAPTER IV. DIFFERENT FORMS OF OSCILLATORS AND RESONATORS THE MODERN RECEIVER ... 69-102 Modern Receivers ... ... ... 74 Coherer Detectors or Receivers ... ... 79 I. Non-Restorative Forms ... 79 Theory of the Action of the Filings Coherer ...... 86 Cell Detectors ... 88 II. Self-Restoring Coherers ... ... 93 Electrolytic or Chemical Detectors 97 Optical Detectors ... 100 Classification of Detectors ... 101 CONTENTS. CHAPTER V. PAGE. SYNTONY ... ... ... ... ... ... 103-125, Harmonic Telegraphy ... ... ... 113 CHAPTER VI. THE WORK OF MARCONI 126-148 CHAPTER VII. THE LODGE-MUIRHEAD SYSTEM 149-161 CHAPTER VIII. WIRELESS TELEGRAPHY IN FRANCE 162-170 CHAPTER IX. GERMAN SYSTEMS ... ... ... ... 171-199 The New German System Telefunken ... 192 Spanish Experiments ... ... ... 198 CHAPTER X. AMERICAN SYSTEMS 200-208 CHAPTER XI. INVENTIONS AND EXPERIMENTS OF M. GUARINI 209-217 CHAPTER XII. SIGNALLING TO AND FROM MOVING RAILWAY TRAINS ... ... ... ... ... ... 218-223 CHAPTER XIII. SCREENING - - THE EFFECT OF OBSTACLES, WEATHER, LIGHT, ETC. ... ... ... 224-228 Conclusion 228 ^Etheric or Wireless Telegraphy. INTRODUCTION. Scientific men are often accused of being too optimistic of dreaming- dreams which are never likely to be realised. Some listeners, no doubt, characterised as of this nature Prof. Ayrton's memorable statement made in 1897 (when speaking of telephony) : "There is no doubt the day will come maybe when you and I are forgotten when copper wires, guttapercha coverings, and iron sheathings will be relegated to the " museum of antiquities." ... In that day when a man wants to telegraph to a friend he knows not where, he will call in an electromagnetic voice which shall be heard loud by him who has the electro- magnetic ear, but will be silent to everyone else. He * ' will call Where are you ? and the reply will come, * ' I am at the bottom of a coal mine,' I am crossing ' the Andes,' I am in the middle of the Pacific,' or perhaps no reply will come, and he may conclude his friend is dead." Making due allowance for mere rhetoric, few dreams of scientists have reached such a stage of fulfilment in so short a time. Five years only have elapsed, and we read in the daily papers Marconi's message to the King which has been flashed across 2,500 miles of Atlantic ocean without the aid of an intervening wire or metallic conductor. Prof. Ayrton's dream is likely to become to a considerable extent a reality even whilst he himself is young and 2 OR WIRELESS s vigorous enough not only to rejoice at, but also to participate in, the triumphs of the science he loves. To whom is the wonderful advance of the last few years due ? Well, to many workers. To Faraday, Maxwell, Henry, Hertz, Branly, Lodge, Preece, and, most of all, to Marconi, the man who reduced theories and experiments to practical realities. " " Early Attempts. Passing over the anticatelephor of Edwards (1829), in which air or water in pipes was probably the medium employed, we find Mr. Edward ** Davy in 1838 preparing to send waves by the conjoint agency of sound and electricity," to be received in the focus of an electromagnetic receiver at a distance. Prof. Morse in 1842 gave a practical demonstration of an ordinary submarine insulated wire telegraph to connect Governor's Island with Castle Garden in New York, a distance of one mile. The accidental breakage of his wires by a passing vessel caused him to so arrange his wires along the banks as to use the water itself as a conductor at least that was his own explanation. Sir W. Preece in recent times has carried out this method much more perfectly. James Bowman Lindsay, of Dundee, about 1843 elaborated somewhat the same idea. Lindsay, who was born in 1799, was, without doubt, a remarkable man. He was appointed lecturer in mathematics at the Watt Institution, Dundee, in 1829. He saw far in advance of his time, but was prevented by want of means and a strange hyper-modesty from carrying his ideas out to perfection. A sort of walking encyclo- life to paedia, he spent a great part of his trying with the compile a dictionary in fifty languages object of finding out the time and place of man's origin. He lectured in electrotechnics, including electric lighting, TELEGRAPHY. I I and proposed in 1843 a submarine telegraph across the Atlantic. In March, 1853, he delivered a lecture in the Thistle Hall, Dundee, in which he proved by experi- ments that with suitable arrangements of apparatus and wires laid along the banks of a river, the water itself could be made to transmit the electrical impulses. Many experimenters have tried the same method, using the earth or water as a conductor. It cannot be said that all these are on the wrong track, but certainly most of their experiments show very little knowledge of the capabilities of high-frequency etheric . trans- mission. Practical Period. We come now to the time of the telephone. The invention of the telephone gave a new receiver of extraordinary sensitiveness for very feeble interrupted or alternating currents, and experimenters were not slow to make use of it. Prof. Trowbridge, of Harvard, in the United States, carried out elaborate researches on the propagation of electric currents through the earth or water. He found, like many others since, that if the terminals of a telephone receiver be connected to a separate metallic circuit, two points of which are earthed at two places not at the same potential as regards the metallic circuit, sounds will be heard in the telephone due to the current passing through it. By inserting an interrupter and a key in the circuit of the battery, the uniform noise or hum heard in the telephone can be cut into long and short periods to give signals in accordance with the Morse alphabet. Thus messages may be sent over considerable distances without intervening wires. Prof. Trowbridge even put forward the view, originally promulgated by Lindsay, that it might be possible to signal in this way from the United States to Europe. 12 ^ETHERIC OR WIRELESS Intercommunication between ships at sea was pro- posed, and in 1882 Graham Bell tried the experiment with boats on the Potomac River, and succeeded in sending- messages over a distance of ij miles. Prof. Dolbear, of Boston, made some useful sugges- tions in 1883. He used an induction coil having in its primary circuit a microphone transmitter with wire dipping into the earth, and he even in some cases used an elevated wire, or ''aerial," not unlike that now employed. Mr. T. A. Edison, in 1885, invented, or rather perfected, in conjunction with Messrs. Gilliland Phelps and Willoughby Smith, a method of signalling to and from moving trains. This method is based on the principle that a magnetic field, if varied, has the power to affect a second electrostatic system and create, in air-gaps, displacement currents sufficient to affect a telephone receiver. Prof. Trowbridge, again, in 1891 proposed the use of the magnetic induction system, using two separate and insulated circuits. He found that if a primary circuit consisting of a large coil of wire with a battery and interrupter be employed, and a secondary circuit consisting of a coil and telephone receiver, the inter- ruptions of the current in the primary circuit give rise to induced currents in the secondary circuit which make themselves heard in the telephone. Sir W. Preece has carried out many experiments with a com- bination of this and the conduction method, and, in conjunction with Mr. Marconi, in 1897 had considerable success, a distance of over eight miles being traversed without intervening conductors. Dr. (now Sir) Oliver Lodge has, probably more than any other Englishman, worked successfully at this TELEGRAPHY. 13 subject. He has shown the way, has written much, .and formulated nearly all the known laws governing the transmission of signals without conductors. He has recently (in conjunction with Dr. Muirhead) elaborated a system which is likely to rival those now in use. Later success has been due mainly to Mr. Marconi, who, with true youthful elasticity combined with genius, "has never known when he was beaten," but, when seemingly defeated, has taken up the fight with renewed ardour, always to conclude with success. For instance, the lengthening of his vertical wire and the " " discovery of a so-called law of distance when failure seemed certain, and later the insertion of a step-up transformer in the transmitting circuit, the use of a split transformer in the receiving circuit, and the invention of the magnetic receiver, can only be regarded as strokes of genius.