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WIRELESS TELEGRAPHY 
 
 AND 
 
 WIRELESS TELEPHONY 
 
 AN UNDERSTANDABLE PRESENTATION OF THE SCIENCE OF 
 WIRELESS TRANSMISSION OF INTELLIGENCE 
 
 By 
 
 CHARLES G. ASHLEY 
 
 ELECTRICAL ENGINEER 
 
 And 
 
 CHARLES B. HAYWARD 
 
 CONSULTING ENGINEER; MEMBER, SOCIETY 
 OF AUTOMOBILE ENGINEERS 
 
 ILLUSTRATED ;*\i* 
 
 CHICAGO 
 
 AMERICAN SCHOOL OF CORRESPONDENCE 
 1912 
 

 COPYRIGHT 1911 BY 
 AMERICAN SCHOOI, OF CORRESPONDENCE 
 
 Entered at Stationers' Hall, London 
 All Rights Reserved 
 
CONTENTS 
 
 The page numbers of this volume will be found at the bottom of the 
 pages; the numbers at the top refer only to the section. 
 
 WIRELESS TELEGRAPHY 
 
 Page 
 
 Introduction 1 
 
 Early forms 2 
 
 Conduction systems 2 
 
 Induction systems 4 
 
 Electric waves 8 
 
 Electromagnetic theory of light 8 
 
 Nature of a wave 11 
 
 Electric oscillations 12 
 
 Work of Hertz .^ 14 
 
 Resonance '. 17 
 
 Wave-lengths 21 
 
 Development of radiotelegraphy 23 
 
 The Righi oscillator .". . 24 
 
 The Branly coherer 24 
 
 Radiotelegraphy first suggested 25 
 
 Work of Hughes 27 
 
 Work of Lodge. 27 
 
 Work of Marconi 27 
 
 Propagation of waves from a grounded oscillator 36 
 
 Selective signaling 38 
 
 Radiotelegraphic apparatus 40 
 
 Sources of energy 40 
 
 Charging devices 40 
 
 Induction coils 41 
 
 Alternating-current transformers 46 
 
 Oscillation transformers 47 
 
 Condensers 47 
 
 Tuning coils 49 
 
 Spark gaps 49 
 
 High-frequency alternators 52 
 
 The singing arc 53 
 
 Aerials 55 
 
 Directive antennae 57 
 
 Detectors 57 
 
 Auxiliary apparatus 66 
 
 Measuring instruments 67 
 
 Systems of radiotelegraphy 68 
 
 Telegraphic codes 69 
 
 Marconi system , 69 
 
 Fessenden system 72 
 
 Telef unken system 74 
 
 Note. For page numbers see foot of pages. 
 
 258673 
 
CONTENTS 
 
 Systems of radiotelegraphy Page 
 
 Von Lepel system 76 
 
 Lodge- Muirhead system 77 
 
 DeForest system 79 
 
 Clark system 80 
 
 Stone system 82 
 
 Massie system , 83 
 
 Poulsen system 83 
 
 Other systems and inventors 83 
 
 WIRELESS TELEPHONY 
 
 Bell's radiophone 89 
 
 Selenium cell 90 
 
 Bell's photophone 91 
 
 "Light telephony" 91 
 
 Telephony by means of Hertzian waves 92 
 
 Nature of a high-frequency telephone current 94 
 
 Oscillation generators 96 
 
 Telephonic control of oscillations 97 
 
 Transmitting circuits 98 
 
 Receiving arrangements 102 
 
 Two-way transmission 104 
 
 Systems of radiotelephony 105 
 
 WIRELESS TELEGRAPHY IN AERONAUTICS 
 
 Wireless on dirigibles 
 
 Early experiments on balloons 119 
 
 Dangers from electric discharge 120 
 
 Preventive methods 122 
 
 Wireless on the Zeppelins 124 
 
 Wireless on aeroplanes 
 
 First message 125 
 
 Horton's experiments 126 
 
 Recent records 127 
 
 General problems 130 
 
 Note. For page numbers see foot of pages. 
 
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INTRODUCTION 
 
 WIRELESS TELEGRAPHY was the subject of earnest experi- 
 mentation as early as 1838, but as far as the public mind is con- 
 cerned the science began when Marconi sent his first message across 
 the Atlantic from Cornwall to Nova Scotia in 1902. This wonderful 
 accomplishment, like the startling application of the X-rays v by 
 Roentgen, had so much of the spectacular element in it, that wireless 
 telegraphy and Marconi became famous at once. The notable rescues 
 of the passengers of the Republic and the Titanic by the aid of 
 wireless messages have only heightened this interest, and it was to 
 satisfy the demand for a practical and understandable presentation 
 of the subject that this little book has been published. 
 
 C.The development of the wireless telegraph is carried out logic- 
 ally from the early forms to the latest adaptations of the most 
 important systems. The discussion also includes its application 
 to the aeroplane and dirigible. 
 
 CL Wireless Telephony, seemingly even more mysterious than teleg- 
 raphy, is being rapidly developed, the entire absence of the disturb- 
 ing noises, so characteristic of the land telephone, making this 
 mechanism especially attractive. Its use between ship and shore 
 for considerable distances has long since passed the experimental 
 stage. 
 

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WIRELESS TELEGRAPHY 
 
 INTRODUCTION 
 
 As a first step into the subject of wireless telegraphy it may be 
 well to consider the meaning of the term. Wire telegraphy is char- 
 acterized by the employment of extended metallic lines or conductors 
 over which it is possible to transmit intelligence electrically by means 
 of an arbitrary code of signals. Wireless telegraphy is characterized 
 by the absence of such lines in the accomplishment of the same end. 
 Many have confounded wireless telegraphy with the system invented 
 by Marconi; but the latter is only one form out of many: the term 
 was used to describe other systems years before Marconi's spec- 
 tacular success added it to the popular vocabulary. As a matter 
 of fact any system of telegraphy which successfully substitutes some 
 other medium for the connecting wires, may properly be called 
 " wireless." The systems of wireless telegraphy so far proposed may 
 be classified as follows: Conduction Systems; Induction Systems; 
 and Radiation Systems. 
 
 The history of the subject follows very closely the above sequence 
 in point of time. First came the conduction systems the attempt 
 to substitute the earth and bodies of water in place of the connect- 
 ing lines. Then came the induction systems, taking advantage of 
 those peculiar electrical phenomena known as electrostatic and 
 electrodynamic induction: here the substituted medium was the 
 ether that invisible, intangible substance which is supposed to fill 
 all space. Last came the radiation systems, which also make use 
 of the ether, but in a different way, namely, by disturbing it in such 
 a manner as to produce far-reaching waves which can be detected 
 at distant points. It is the last type, known as radiotelegraphy, 
 which is today paramount, having superseded the other two by 
 reason of its superior utility and effectiveness. Its startling develop- 
 ment during the past ten years may justly be called a "fairy tale of 
 science." The earlier systems are important, however, as they 
 mark the birth and the development of an idea. 
 
CHAPTER I 
 EARLY FORMS 
 
 Conduction Systems. The essential feature of all conduction 
 systems is that some other form of material conductor is substituted 
 for that of wires. These substitutes have been in all cases either 
 earth or bodies of water, because they are the only natural conductors 
 which are sufficiently common and extensive to be utilized. 
 
 Work of Steinheil. Today it seems glaringly obvious that the 
 earth may be used as a conductor, but in 1838 when Steinheil, a 
 Bavarian, accidentally discovered this fact, it created quite a sensa- 
 tion. He had been experimenting with the steel rails of a railroad 
 trying to utilize them as substitutes for the wires of a telegraph cir- 
 cuit, but was unable to obtain sufficient insulation. He was sur- 
 prised to discover, however, what a high degree of conductivity the 
 earth possessed, and was led to conceive that he might employ it 
 instead of the return wire hitherto used. He made the experiment, 
 and with complete success, thus introducing into telegraphy one of 
 its most important features the earth circuit. Expanding the idea, 
 Steinheil wondered if it were not possible to telegraph through the 
 earth without using metallic conductors at all. This experiment, 
 which was successful over very short distances, is said to have been 
 the first attempt to telegraph without wires. Steinheil, however, 
 being unable to signal farther than 50 feet, gave up this method, 
 convinced that it was inexpedient for telegraphy. 
 
 Morse System. S. F. B. Morse, who is famed as the inventor 
 of wire telegraphy and of the code which still bears his name, was, 
 by a strange coincidence, also one of the pioneers of telegraphy 
 without wires. In 1844 he addressed a letter to Congress in which 
 he related his experiments in this field and gave an interesting account 
 of his inception of the idea. A portion of the document, consider- 
 ably abridged, is as follows: 
 
 In the autumn of 1842, at the request of the American Institute, I under- 
 took to give to the public in New York a demonstration of the practicability 
 
EARLY FORMS 3 
 
 of my telegraph, by connecting Governor's Island with Castle Garden, a dis- 
 tance of a mile; and for this purpose I laid my wires properly insulated beneath 
 the water. I had scarcely begun to operate, and had received but two or 
 three characters, when my intentions were frustrated by the accidental de- 
 struction of a part of my conductors by a vessel which drew them up on her 
 anchor and cut them off. In the moments of mortification I immediately 
 devised a plan for avoiding such accidents in the future, by so arranging my 
 wires along the banks of the river as to cause the water itself to conduct the 
 electricity across. The experiment, however, was deferred until I arrived in 
 Washington; and on Dec. 16, 1842, I tested my arrangement across the canal, 
 and with success. The simple fact was then ascertained that electricity could 
 be made to cross a river without other conductors than the water itself; but 
 it was not until the last autumn that I had the leisure to make a series of ex- 
 periments to ascertain the law of its passage. The diagram, Fig. 1, will serve 
 to explain the experiment. 
 
 A, B, C, D, are the banks of the river; N P is the battery; G is the gal- 
 vanometer; W W are the wires along the banks, connected with copper plates 
 /, g, h, i, which are placed in the water. When this arrangement is complete, 
 the electricity, generated by the battery, passes from the positive pole P to 
 the plate h, across the river through the water to plate i, and thence around 
 the coil of the galvanometer to plate /, across the river again to plate g, and 
 thence to the other pole of the battery N. 
 
 Morse here appends a table of his results, "showing," as he 
 says, "that electricity crosses the river, and in quantities in propor- 
 
 w 
 
 W P\'\'\'\N 
 
 Fig. 1. Experiment of Morse 
 
 tion to the size of the plates in the water. The distance of the plates 
 on the same side of the river from each other also affects the result." 
 This distance he states elsewhere should be three times greater than 
 that from shore to shore across the stream. 
 
 Morse's plan contains in a simple form all the essential features 
 of all later endeavors to telegraph by the conduction method whether 
 utilizing water or earth as the medium. Lindsay, Highton, Bering, 
 Stevenson, Preece, Smith, and others subsequently worked out 
 more elaborate and extensive methods all resting primarily on the 
 
4 WIRELESS TELEGRAPHY 
 
 same principle as above. None of them succeeded in signaling much 
 farther than three miles. These early results indicate the inherent 
 limitations which have ever remained as insurmountable difficulties 
 to the commercial adoption of this form of wireless telegraphy. 
 
 Induction Systems. Induction is an electrical influence exerted 
 by a charged body or by a magnetic field on neighboring bodies 
 without apparent communication. The laws of it are well known 
 to electrical science through the classic researches of Faraday. In- 
 duction comprehends two classes of phenomena known, respectively, 
 as electrostatic induction and electrodynamic induction: the former is 
 that property of the electrostatic field which produces an electric 
 charge in a conductor when brought into the said field; while the 
 latter is that property of the magnetic field by virtue of which electro- 
 motive forces are created in conductors by a relative movement be- 
 tween said field and such conductors. Without attempting to go 
 further into the matter here, it suffices to say that investigators were 
 not slow in appreciating that induction offered a means of communi- 
 cation which could be classified as " wireless. " 
 
 Dolbear System. What is now generally considered to be an 
 extreme case of electrostatic induction, is the remarkable system of 
 wireless communication invented by Prof. Dolbear of Tufts College, 
 Boston, in 1882. This system is of especial historical interest owing 
 to its startling resemblance to the system devised later by Marconi. 
 Dolbear's invention may be best explained by referring to Fig. 2. 
 The left side represents the transmitting circuit and the right, the 
 receiving circuit. B is a battery connected through a carbon trans- 
 mitter to the primary winding of an induction coil, the secondary 
 terminals, A and (7, of which are connected, respectively, with an 
 elevated wire and the grdund. The receiving end consists essen- 
 tially of a similar elevated wire A connected to one terminal of a 
 telephone receiver, the companion terminal of which is connected 
 directly with the earth. The higher these wires are raised, the farther 
 signals can be transmitted, so that Dolbear was prompted to attach 
 them to kites. This is a curious anticipation of Marconi's antennae. 
 Dolbear later made many modifications in his apparatus in an en- 
 deavor to reach greater distances by employing condensers raised to 
 a considerable height and charged by batteries; but the system re- 
 mained in all important respects the same as shown. 
 
EARLY FORMS 5 
 
 The apparatus works as follows: The diaphragm of the tele- 
 phone transmitter is set into vibration by talking or whistling, thereby 
 producing variations of resistance in the powdered carbon; this 
 constantly varies the amount of current which flows into the induc- 
 tion coil; and consequently the wire A is charged to potentials which 
 are constantly fluctuating in value, the degree of fluctuation depend- 
 ing on the degree of variation of resistance in the transmitter. The 
 wire A' at the receiving station follows by electrostatic induction 
 all the fluctuations of A; and with every change of potential, currents 
 flow between A' and the ground through the telephone receiver R. 
 
 Fig. 2. Diagram of the Dolbear System 
 
 The latter consequently repeats all the vibrations set up in the trans- 
 mitter, and the corresponding sound is reproduced. This particular 
 method of operation is telephonic; but it will be seen that the same, 
 or rather better, results could be obtained by a Morse key and tele- 
 phonic receiver. 
 
 Edison System. Edison patented, in 1885, a system of inductive 
 telegraphy, the particular purpose of which was to effect communi- 
 cation with moving trains. The ordinary telegraph wire, which 
 commonly runs parallel to a railroad track, was utilized for one 
 of the inductive circuits, and the train was equipped with another. 
 The latter consisted mainly of a large, metallic condensing plate 
 set on the roof of the car and connected to the secondary terminals 
 of an induction coil, to the primary terminals of which were con- 
 nected suitable transmitting and receiving instruments. When the 
 Morse key in the primary circuit was depressed, the large con- 
 densing plate received static impulses and these acted inductively 
 
6 WIRELESS TELEGRAPHY 
 
 on the neighboring telegraph wire, which thereby received and con- 
 ducted equivalent impulses to the nearest station equipped with 
 proper receiving instruments. Or in case another train equipped 
 as above were traveling on the same track, it could pick off the 
 message inductively from the telegraph wire. In this manner two 
 moving trains might communicate. This ingenious system was put 
 into practical operation on the Lehigh Valley Railroad in 1887, and 
 worked with undoubted success; but from a business point of view 
 it proved a failure as there was no public demand for such service. 
 
 Work ofPreece. One of England's most successful investigators 
 in the field of wireless telegraphy was Sir Wm. Preece, chief elec- 
 trician of the British Postal Telegraphs. He performed numerous 
 experiments which added greatly to the theory of all forms of inductive 
 and conductive communication. One of his most successful achieve- 
 ments was to effect inductive communication between Gloucester 
 and Bristol on the banks of the Severn, a distance of nearly five miles. 
 Parallel to the two shores were stretched on telegraph poles two 
 closed wire circuits extending about 14 miles each. One of these 
 circuits was traversed by a rapidly interrupted current of about .5 
 amperes. A telephone receiver inserted in the companion circuit 
 responded to the frequency of the current in the other by a con- 
 tinuous sound upon pressure of the transmitting key. This form of 
 communication was at one time resorted to quite frequently between 
 stations separated by bodies of water under which it was inexpedient 
 to lay cables. 
 
 Such systems may be characterized as "wireless" only through 
 courtesy, since they demand an amount of wire which far exceeds 
 that required by any ordinary wire system covering the same dis- 
 tance; they come under the classification of wireless telegraphy, 
 however, since the wire conductors are not continuous, some other 
 medium being interposed. 
 
 In the year 1885, Preece carried on very extensive investigations 
 upon the possibilities of induction as an agency of communication, 
 and summarized his observations as follows: 
 
 Although communication across space has thus been proved to be prac- 
 tical in certain conditions, those conditions do not exist in the cases of isolated 
 lighthouses and light-ships, cases which it was specially desired to provide 
 for. The length of the secondary must be considerable, and, for good effects, 
 
EARLY FORMS 7 
 
 at least equal to the distance separating the two conductors. Moreover, 
 the apparatus to be used on each circuit is cumbrous and costly, and it may 
 be more economical to lay a submarine cable. 
 
 These conclusions are equally true to the present day. The 
 necessity for a large base area remains the prohibiting factor in the 
 adoption of electromagnetic induction systems. For a very pains- 
 taking review of the various early attempts at this form of telegraphy, 
 the reader is referred to J. J. Fahie's excellent book, "A History of 
 Wireless Telegraphy." 
 
 Summary. The conduction and induction methods of wireless 
 telegraphy, although of great historical and experimental value, 
 are of little practical value. Today their use is most exceptional 
 because their utility is too limited the supreme test for any system 
 of wireless telegraphy being the test of long distance. They have 
 been superseded by a type of wireless telegraphy which can achieve 
 communication across an ocean if necessary a type which is the 
 product of an entirely different principle, the principle of electro- 
 magnetic radiation. In order to differentiate it from other forms 
 of wireless telegraphy, this system is best denominated by the term 
 radiotelegraphy, and a discussion of its underlying theory, its 
 operation, and the arrangement of necessary apparatus will be 
 found in the following chapters. 
 
CHAPTER II 
 ELECTRIC WAVES 
 
 Electromagnetic Theory of Light. In order to understand ra- 
 diotelegraphy with any degree of completeness one must first have 
 a comprehension of the theory of electric waves, including the elec- 
 tromagnetic theory of light. This theory, with its verification, was 
 one of the most notable scientific achievements of the last century. 
 However, let it be remembered that, having adopted a working 
 hypothesis the most tenable one at present to account for the 
 ether and the modus operandi of ether waves, it is necessary as well 
 as convenient to use the terms and implications of such hypothesis 
 positively and with consistency throughout. Such unqualified use of 
 terms might give foundation to the charge of scientific dogmatism 
 were it not remembered at all times that we are dealing with a 
 theory, generally accepted, it is true, but subject to the trials and 
 mutations which such theories have undergone in the past. The 
 reasonings from the working hypothesis are valid for the purpose 
 for which they are here employed; but no true scientist will at present 
 claim that such reasonings should or can be extended to the higher 
 realm of absolute truth. In the words of H. Poincare*, "It matters 
 little whether the ether really exists; that is the affair of metaphysicians. 
 The essential thing for us is that everything happens as if it existed, 
 and that this hypothesis is convenient for the explanation of the 
 phenomena." 
 
 The electromagnetic theory of light was first completely stated 
 in 1864, when James Clerk Maxwell, an English mathematician, 
 sent to the Royal Society a paper entitled "A Dynamical Theory of 
 the Ether," wherein he demonstrated his conviction that light and 
 electricity were phenomena of a kindred nature in fact, that light 
 was an electrical manifestation. Maxwell's paper came as the result 
 of a long series of investigations which had been carried on in two 
 different departments of Physics Optics and Electricity. These 
 investigations had led on the one hand to a theory of a light-bearing 
 medium called the luminiferous ether, and on the other hand to a 
 
ELECTRIC WAVES 9 
 
 
 
 theory of an electromagnetic medium also called the ether. Max- 
 well made a synthesis of these two theories, demonstrating that the 
 hypothetical medium was the same in both cases, and that it was 
 governed by electromagnetic laws. 
 
 The Luminiferous Ether. When we observe that light takes 
 time to travel from place to place, and that it comes to the earth 
 from the sun and stars across vast spaces which are not, so far as 
 we know, filled with tangible matter, the inference necessarily fol- 
 lows that light is either a substance transmitted bodily, like a stone 
 hurled from one place to another, or a physical state propagated 
 through a stationary medium in the form of waves. Various inves- 
 tigators have demonstrated that light is a phenomenon of the latter 
 description that it is a physical state, or change of state, propagated 
 through a stationary medium in the form of undulatory waves, the 
 velocity of the waves being approximately 186,500 miles per second. 
 Investigators agreed to call this medium the ether, prefixing the ad- 
 jective "luminiferous" which means "light-bearing." They had 
 neither seen nor felt the ether directly or indirectly but they 
 reasoned that the ether must exist, else the facts of Optics were 
 inexplicable. They held that it must be some peculiar form of 
 matter which interpenetrated all ordinary forms of matter, and 
 must also be distributed everywhere throughout the space of the 
 universe. Up to Maxwell's time, however, they knew almost nothing 
 of the ether itself, except that it behaved like an incompressible 
 liquid, extremely tenuous but exceedingly rigid, and that the waves 
 were of the kind classed as "transverse." 
 
 The Electromagnetic Medium. In the department of Electricity 
 a theory of an electromagnetic medium had also grown up, follow- 
 ing on the researches of Ampere, Henry, and Faraday. The fact 
 that electrified bodies or magnets attracted or repelled each other 
 at a distance, and that electric currents could create other currents 
 in wires at a distance, and that these actions were not fundamentally 
 dependent upon the presence of any material substance in the space 
 between, led these investigators to conceive that there must be an 
 electromagnetic medium by means of which such actions were trans- 
 mitted across apparently empty spaces. They named this medium 
 the ether, the same name adopted by investigators in the department 
 of Optics; but it was a long time before anyone even surmised that 
 
10 WIRELESS TELEGRAPHY 
 
 there was any kinship between the luminiferous medium and the 
 electromagnetic medium. 
 
 Work of Faraday. The first man to hint at the above possi- 
 bility was Faraday, who, in 1845, discovered the singular fact that 
 the magnet exercises a peculiar action on light, the plane of polariza- 
 tion of a polarized beam being rotated when the beam passes along 
 a magnetic field. This seemed to show that there was some relation 
 between electricity and light. Faraday persevered in these experi- 
 ments. He wrote a paper entitled "Thoughts on Ray Vibrations" 
 wherein he expressed his belief that radiation of all kinds light, 
 heat, etc. were due to a high species of vibration of the lines of 
 force in the magnetic field. Faraday's speculations may be said to 
 have been the inception of the electromagnetic theory of light; he 
 is indeed entitled to a large share of the credit; but his were only 
 speculations, unformulated and incomplete, and it remained for 
 another man to elaborate them into a complete theory mathematically 
 demonstrable. 
 
 Work of Maxwell. When Maxwell, in 1864, sent his paper on 
 "A Dynamical Theory of the Electromagnetic Field" to the Royal 
 Society, one of his first steps was to acknowledge his debt to Faraday. 
 He writes, "The conception of the propagation of transverse magnetic 
 disturbances to the exclusion of normal ones is distinctly set forth 
 by Prof. Faraday in his 'Thoughts on Ray Vibrations.' The 
 electromagnetic theory of light as proposed by him is the same in 
 substance as that which I have begun to develop in this paper, except 
 that in 1846 there was no data to calculate the velocity of propaga- 
 tion." Maxwell then proceeds to give new equations to express the 
 relations between the electric and the magnetic displacements in 
 the medium and the forces which result from them. He shows that 
 when magnetic methods of measurement are used, the unit of elec- 
 tricity arrived at has a certain value; but when purely electrical 
 methods are used the unit proves to have a different value. The 
 relation between these two units is dependent on the "electric elas- 
 ticity" of the medium, and when measured proves to be a certain 
 velocity 186,500 miles per second. This velocity, in other words, 
 is that velocity with which an electromagnetic disturbance is propa- 
 gated through the electromagnetic field. It will be remembered 
 that the velocity of light was already known to be about 186,000 
 
 10 
 
ELECTRIC WAVES 11 
 
 miles per second. Maxwell comments on the startling similarity 
 as follows: "This velocity is so nearly that of light, that it seems we 
 have strong reason to conclude that light itself (including radiant 
 heat, and other radiations, if any) is an electromagnetic disturbance 
 in the form of waves propagated through the electromagnetic field 
 according to electromagnetic laws." In short, Maxwell's theory 
 assumes that the entire material universe lies in one all-pervading 
 electromagnetic field, called for convenience the ether, and if this 
 field be disturbed at any point, the disturbance is propagated through- 
 out the field in the form of waves. All those forms of radiant energy 
 which we call light, heat, etc., are in reality electromagnetic dis- 
 turbances propagated in the form of electromagnetic waves. 
 
 Once an electromagnetic field is established, any change which 
 alters the prevailing conditions is said to be an electromagnetic dis- 
 turbance. When a current of electricity increases in strength, the 
 field around it increases also, the lines of force spreading out from 
 the conductor like ripples in a pond; but when the current is decreased, 
 the lines of force contract, closing in around the conductor, and the 
 energy of the field shrinks back into the system. If this process be 
 augmented so that the periodic reversals of current produce oscilla- 
 tions of extremely high frequency, then, at each reversal, part of the 
 energy of the lield radiates off into the surrounding medium as elec- 
 tric waves and only part of it returns into the system. The frequency 
 with which such periodic reversals of current take place determines 
 the distance between the crests of the waves radiated into space from 
 such a system. Waves created in the ether by this means are called 
 electric, or Hertzian, waves, after the German physicist, Heinrich 
 Hertz. Before entering upon a more detailed consideration of waves 
 of this character, the subject of waves in general will be considered. 
 
 Nature of a Wave. When a disturbance is made at any point 
 in an elastic medium, the particles of the medium are set into vibra- 
 tion and the vibrations are passed on to the neighboring particles, so 
 that waves are formed ; and these waves travel with a uniform velocity 
 depending on the nature of the medium, with a result that the dis- 
 turbance is propagated to considerable distances from its point of 
 origin. There are in general two classes of waves, known as longi- 
 tudinal and transverse, the distinction between them depending on 
 the direction in which the particles vibrate. When the particles 
 
 11 
 
12 WIRELESS TELEGRAPHY 
 
 vibrate along the line in which the disturbance is traveling, the wave 
 is said to be longitudinal; when the particles vibrate at right angles 
 thereto, the wave is said to be transverse. The general equation 
 for determining the velocity of waves of either class is 
 
 v = In 
 
 where v stands for the velocity, / for the wave length, and n for the 
 frequency, or number of vibrations per second. 
 
 This equation holds equally true for ether waves which mani- 
 fest themselves as light, and for the longer waves produced by high- 
 frequency oscillations of an electric current, both of which are of the 
 transverse variety. Indeed all forms of radiant energy are, accord- 
 ing to the present belief, due to ether waves, differing from one 
 another only in length. As the velocity of propagation is the same 
 for all namely, 186,000 miles per second the frequency varies 
 through a wide range. Ether waves varying between certain definite 
 lengths are visible and produce the sensation of light; others much 
 longer falling upon matter raise its temperature, thus manifesting 
 themselves as heat; still others, of a wave-length extremely small 
 even in comparison with visible rays, are capable of penetrating 
 matter as X-rays; and others again, of a Jength of half a mile or more, 
 are flashed across the Atlantic, conveying intelligence from the Old 
 World to the New. 
 
 As there are many methods of producing waves in gross matter, 
 so also are there many methods of producing waves in the ether. 
 The production of electromagnetic waves of a length measuring 
 from a few inches to many rods need only concern us here, as it is 
 with the production of such waves that the science of radiotelegraphy 
 deals. As before stated, a part of the energy of a very rapidly alter- 
 nating current is radiated off into space in the form of electric waves. 
 Under what physical conditions such disturbances are created will 
 now be considered. 
 
 Electric Oscillations. If a charged condenser, or Leyden jar, 
 is discharged through a conductor of high resistance, the opposing 
 polarities slowly neutralize each other by a current flowing in one 
 direction. If, however, the condenser is discharged through a con- 
 ductor of low resistance, such as a coil of wire of a few turns, the 
 effect is wholly different. Under these conditions the discharge 
 consists of a number of excessively rapid oscillations of the nature 
 
 12 
 
ELECTRIC WAVES 13 
 
 of a high-frequency alternating current, caused by the self-induction 
 of the coil, in consequence of which the current once set up tends to 
 persist. The first rush of current more than empties the condenser, 
 and charges it to the opposite polarity; then follows a series of similar 
 discharges of diminishing amplitude until the energy of the charge 
 is entirely dissipated. This process is represented in Fig. 3. 
 
 The spark produced by the discharge of a condenser under 
 these conditions appears to the eye as a single flash, due to the rapidity 
 with which the successive discharges follow one another. In reality 
 it consists of several distinct sparks lasting but an exceedingly small 
 fraction of a second. 
 
 The law governing condenser discharges is as follows: // a 
 condenser of capacity K is discharged through a resistance R and 
 self-induction L, the result is a unidirectional discharge or a series 
 
 of oscillations according as R is greater or less than 2-vl jr* 
 
 A rapid oscillatory discharge sets the electromagnetic medium 
 in vibration much as a tuning fork sets the air in vibration in pro- 
 
 T/ME AX/3 
 
 MEGAT/VE 
 
 Fig. 3. Curve Representing an Oscillatory 
 Discharge 
 
 ducing sound-waves. Such discharges provide a simple means for 
 creating electric waves in the ether. An understanding of condenser 
 action is, therefore, of great importance in a comprehension of the 
 principles of radiotelegraphy. 
 
 The oscillatory nature of condenser discharges was known 
 when Maxwell promulgated his electromagnetic theory, but it was 
 not until twenty-five years after the announcement of the theory 
 that scientists were able to detect the presence of electric waves. 
 They knew the conditions under which such waves should arise, 
 
 13 
 
14 
 
 WIRELESS TELEGRAPHY 
 
 but none were able to devise a means to demonstrate their presence. 
 It remained for Heinrich Hertz, a pupil of the illustrious von Helm- 
 holtz, to solve the mystery and give experimental verification to a 
 theory which must ever remain one of the greatest achievements of 
 inductive reasoning. Hertz succeeded not only in producing and 
 detecting electric waves, but in demonstrating that such waves 
 possessed all the essential characteristics of light. 
 
 The Work of Hertz. It was in 1888 that Hertz, then thirty 
 years old and professor of Physics in the University of Bonn, carried 
 
 /MDUCT/OM 
 CO/L 
 
 b 
 
 - 
 
 li 
 
 
 
 Fig. 4. Hertz Oscillator 
 
 on the epoch-making series of experiments which have proven to 
 be the foundation of the art of radiotelegraphy. His apparatus was 
 of the simplest construction. To generate electric waves he em- 
 ployed what is now known as a Hertz oscillator, Fig. 4. This con- 
 sists of two metallic conductors in the shape of plates or spheres, 
 each attached to a small rod terminating in a polished metal ball. 
 These were connected to the secondary terminals of an induction 
 coil and the two balls brought into close proximity, thus forming 
 a small spark gap. It will be seen that the arrangement has the 
 essential features of a condenser whose plates are widely separated 
 and whose dielectric extends into the surrounding air. When the 
 charge is accumulating on the large metallic plates, a strong electric 
 
ELECTRIC WAVES 15 
 
 displacement is set up between them, and, as the potential difference 
 rises, a point is reached where the insulation of the air gap breaks 
 down and a spark passes across the gap. During the passage of this 
 spark the air becomes highly conductive and the whole oscillator 
 becomes one conductor for the time being. The potential difference 
 between the charged plates immediately begins to equalize itself, 
 after the manner of all oscillatory condenser discharges, by a series 
 of rapidly damped surges, and with every oscillation a wave is 
 radiated into space. The waves emitted by a device of this char- 
 acter are intermittent, each complete discharge of the oscillator 
 
 r 
 
 
 /v f N p P N 
 
 Fig. 5. Formation of Closed Loops of Electric Strain 
 
 sending out a rapidly damped train, or group, of waves. The 
 frequency with which such trains follow one another depends upon 
 the frequency of the charging source. 
 
 It cannot be said that the exact sequence of events in the for- 
 mation of an electric wave is definitely agreed upon, further than 
 that the production consists in sending out closed loops of force as 
 shown by Hertz, Dr. F. Hack, and others. The subject is very 
 difficult to present briefly, but an idea of the process may be had by 
 reference to Fig. 5. 
 
 The curved line represents the form and the direction of one 
 of the many lines of electric strain existing between the two plates 
 of a Hertz oscillator. Every line of electric strain according to the 
 electronic theory of electricity must be a closed line or loop, or else 
 
 15 
 
16 WIRELESS TELEGRAPHY 
 
 must terminate on an electron and a co-electron. The figures A, 
 B, C, D, E, and F represent the successive stages in the pro- 
 duction of closed loops of electric strain. As the charges oscillate 
 to and fro the lines of electrostatic strain are crossed, making a closed 
 loop which is immediately pushed outward by the following loop; 
 with the result that the direction of strain around each loop is alter- 
 nately in one direction and in the other, as shown in F. In addition 
 to these lines of electrostatic strain there are at right angles to them 
 other self-closed lines of force of a magnetic nature, due to the cur- 
 rent passing during discharge. These magnetic rings of flux alter- 
 nate in their direction at each oscillation, thus forming a series of 
 closed loops of magnetic flux co-axial with the oscillator. Hence 
 we are called upon to imagine the space around a Hertz oscillator 
 as filled with concentric rings of magnetic flux periodically revers- 
 ing in direction and having their maximum values at instants when 
 the electrostatic strains are at their minimum values. These com- 
 plementary modes of energy periodically varying in regard to time 
 and space form an electric wave. 
 
 Energy of an Oscillator. As a portion of the energy imparted 
 to an oscillator in the form of an electric charge is expended in heat- 
 ing the metallic balls, in creating a bright light, and in producing a 
 noise at the discharge, it is evident that the entire energy of the 
 system is not expended in the formation of electric waves. The 
 total amount of energy which it is possible to potentially store in 
 an oscillator in the form of electrostatic stress depends on its elec- 
 trical capacity, and is equivalent to the amount of energy which 
 could be stored in a condenser of the same capacity. The storage 
 of energy in a condenser is proportional to the square of the voltage 
 to which it is charged; which is another way of saying that a very 
 great amount of energy could be stored in a very small condenser 
 if it were possible to maintain the insulation under exceedingly high 
 potentials. The dielectric strength of the material used for the 
 dielectric thus places a limit upon the amount of energy it is possible 
 to store in such a device. A small oscillator could likewise have a 
 large amount of energy imparted to it by enlarging the spark gap 
 enough to allow a higher potential to be reached before the insula- 
 tion of the gap breaks down, were it not for the fact that the increased 
 resistance of the lengthened gap renders the spark non-oscillatory. 
 
 16 
 
ELECTRIC WAVES 17 
 
 A limit is therefore placed upon the potential which it is practicable 
 to employ in the charging of oscillators or any form of condenser. 
 As the capacity of a condenser increases in direct proportion to the 
 area of its plates other factors remaining the same it is evident 
 that the dimensions of an oscillator of the Hertz type determine the 
 amount of energy it is possible to utilize in the generation of electric 
 waves. 
 
 Hertz Resonator. The most important contribution of Hertz 
 to the subject of electric waves was the discovery of a simple means 
 for detecting the presence of such radiations. The fundamental 
 character of the discovery is apparent when it is observed that the 
 device consists simply of a single turn of wire forming a ring, pro- 
 vided with a spark gap between two metallic knobs, the distance 
 separating these terminals being adjustable by a screw. The de- 
 vice, called a resonator, is shown in Fig. 6. Hertz discovered that 
 electric waves falling upon such a conductor were capable of inducing 
 therein alternating currents of the same 
 frequency. By holding his resonator 
 within a few yards of an active oscillator 
 he found that it became the seat of 
 induced secondary oscillations which 
 were strong enough to be manifested 
 by minute sparks visible between the 
 metallic balls. Following up this clue 
 he carried on a very extensive series of 
 experiments, all tending to prove that 
 such waves possessed all the character- Fig 6 
 
 istics of light that they were indeed 
 
 but "invisible light." Hertz' resonator may be said to be the first 
 "wireless detector" known. The further development of this preg- 
 nant idea plays an important part in the evolution of the systems of 
 wireless telegraphy. 
 
 Resonance. A definite period of vibration is characteristic 
 of many things in nature, including all sonorous bodies such as 
 strings under tension, as in the case of the piano and all stringed 
 instruments; confined portions of air, as exemplified by the organ 
 pipe ; and in fact all bodies which, when displaced by the application 
 of an external force, tend to return by virtue of their elasticity and 
 
 17 
 
18 WIRELESS TELEGRAPHY 
 
 execute free vibrations until they gradually come to rest. If very 
 feeble impulses be applied to a pendulum at rest at intervals exactly 
 corresponding to its natural period of vibration, it may be made to 
 swing through an arc of considerable amplitude. Bodies capable 
 of executing vibrations by virtue of their own resiliency may likewise 
 be set into powerful vibration by a series of impulses keeping time 
 with their own natural period. Thus a tone from a violin may draw 
 forth a responsive note from a piano, and by the same reason a piano 
 will often set into sympathetic vibration some fixture or article of 
 bric-a-brac. Also impulses communicated through the air from a 
 sounding tuning-fork and falling upon another of the same pitch, 
 will cause the latter to hum a note in unison. This phenomenon 
 is called resonance. Resonance is thus an increase, or amplifica- 
 ^ tion, of a periodic motion by an intermittent force of the same 
 time-period. 
 
 Resonant effects are not confined to the vibrations of gross matter, 
 but may also be observed in connection with the flow of electricity 
 in a circuit. This would seem to indicate that an electric circuit 
 possessed something analogous to a natural period of vibration 
 which is the case. This time-period* is due to certain characteris- 
 tics of the circuit, namely capacity, and inductance. The quantity 
 of electricity required to charge a conductor up to unit potential or, 
 in other words, the ratio of the charge on a conductor to its poten- 
 tial, is called capacity. The unit employed to measure capacity 
 is the farad. Inductance is that quality of an electric circuit by 
 virtue of which the passage of an electric current is necessarily 
 accompanied by the absorption of energy in the formation of a 
 magnetic field. The analogy to mechanical inertia is very close, 
 and, for convenience, inductance may be thought of as electromag- 
 netic inertia by reason of which an electric current resists any sudden 
 change. The unit of inductance is the henry. In all circuits pos- 
 sessing capacity and inductance there is a storage of electrostatic 
 energy due to the potentially charged capacity, and a storage of 
 electromagnetic energy due to the formation of the magnetic field 
 by the current. Any electrical change taking place in such a circuit 
 requires a readjustment of this stored energy. Such an adjustment 
 takes place in the form of an oscillatory current of diminishing 
 amplitude until equilibrium is restored. The time-period of such 
 
 18 
 
ELECTRIC WAVES 19 
 
 oscillations of energy is dependent upon the capacity and the 
 inductance of the circuit, and is expressed by the equation 
 
 where L is the inductance in henries, and K is the capacity in farads. 
 The number of such oscillations per second, i. e., the frequency, is, 
 
 therefore, n= . For purposes in connection with wireless teleg- 
 
 raphy this equation is better expressed in microseconds, micro- 
 henries, and microfarads. 
 
 The phenomena of electrical resonance were first illustrated 
 by Sir Oliver Lodge in his well-known experiment with his so-called 
 syntonic jars. Two Leyden jars, Fig. 7, are placed a short distance 
 apart. A bent wire connected to the outer coating of one serves as a 
 discharging circuit (as shown) with a short air, gap between polished 
 knobs at the top. A circuit of wire whose inductance is rendered 
 adjustable by a sliding cross-piece making connection between 
 two conductors is connected permanently with a second jar. This 
 
 Fig. 7. Lodge Syntonic Jars 
 
 jar is also provided with a spark gap formed between the outer 
 coating and a small piece of tin-foil extending from the inner coating 
 over the lip of the jar to within a short distance of the outer coat- 
 ing. By continually discharging the first jar by connection with 
 an induction coil or other suitable source of high potential, and by 
 manipulating the sliding cross-plate in the circuit of the other jar, 
 a point may be found where the latter will also discharge in syntony 
 with the first. The two circuits are then said to be in tune, in syntony, 
 or in resonance. When the product of inductance by capacity is 
 the same for two circuits, they have the same natural period of 
 oscillation. 
 
 19 
 
20 
 
 WIRELESS TELEGRAPHY 
 
 Fig. 8. Closed Oscil- 
 latory Circuit 
 
 As any circuit possessing inductance and capacity tends to 
 oscillate electrically at its own frequency, it becomes the seat of an 
 induced oscillatory current when subjected to the influence of elec- 
 tric waves of that frequency, each wave giving a slight impulse 
 to the readily excited oscillations, with the result that the induced 
 electromotive forces will be amplified in intensity, 
 just as the swing of a pendulum is amplified by 
 the application of properly timed, though feeble, 
 touches. Circuits possessing inductance and ca- 
 pacity connected in series are thus capable of 
 being "tuned" to a required frequency by a proper 
 adjustment of these two factors. Such circuits 
 are called oscillatory circuits and may be of many 
 forms, but can be classified under two heads 
 known as closed oscillatory circuits and open 
 oscillatory circuits. Those circuits having their 
 capacities in the form of condensers whose capacity areas are 
 closely associated are called "closed," and those having their capacity 
 areas widely separated in such a manner as to cause the field of 
 electrostatic stress to extend out into the surrounding space are 
 called "open." In the first, Fig. 8, the capacity is represented by 
 the two metallic disks separated by a dielectric of air, and connected 
 by a circular wire representing the inductance of one turn, while the 
 
 "open" type, Fig. 9, is shown by 
 the two metallic capacities con- 
 nected by a rod which is cut in 
 two at the center to form a gap. 
 Either may or may not have an 
 air gap introduced therein. 
 
 The similarity to the Hertz os- 
 cillator and resonator is apparent 
 
 at a glance. This is, indeed, more than a similarity, for the Hertz 
 oscillator was nothing more than an open oscillatory circuit, and 
 his resonator a closed circuit of the same variety. By separating 
 the plates of a condenser after the manner of a Hertz radiator, thereby 
 forming an open oscillatory circuit, a large part of the energy of the 
 charge is radiated away in the form of electric waves by reason of the 
 dielectric extending out into the surrounding air. Circuits of this 
 
 Fig. 9. Open Oscillatory Circuit 
 
ELECTRIC WAVES 21 
 
 type are, therefore, excellent radiators but not very persistent radia- 
 tors, because the oscillatory current is damped quickly by the 
 rapid dissipation of energy in the radiation. Conversely, circuits 
 of the closed type are persistent vibrators, but poor radiators. The 
 train of waves emitted by the open type may be compared to the note 
 given forth from a piano string when the finger is immediately re- 
 moved from the key allowing the damper to rapidly extinguish the 
 vibration. The closed type is comparable to a note struck on the 
 same instrument but with the damper raised by the sustaining 
 pedal. As it requires an increment of time to start oscillations in a 
 tuned circuit, it is obvious that the closed type is preferable if it can 
 be made to radiate sufficiently. If the damping of the oscillations 
 in a radiator takes place too quickly, the energy of the charge will 
 be dissipated at the first or second surge, in which event the 
 exact timing of a resonating circuit is unimportant. With a persistent 
 oscillator, however, syntony between the two circuits is of the utmost 
 importance, as otherwise the exciting circuit will tend to destroy at 
 one moment the oscillations it set up a moment earlier. Syntony 
 is of great practical value in the application of Hertzian waves to 
 wireless telegraphy in that it permits of selective signaling to a cer- 
 tain extent by the employment of different wave-lengths, or the 
 tuning of a receiving station to the frequency of a sending station. 
 Wave=Lengths. As before mentioned, the waves created by 
 a Hertz oscillator are of very much lower frequency and are pro- 
 portionally longer than light waves, but .their velocity is identical. 
 Furthermore, the relation between the velocity of propagation, fre- 
 quency, and wave-length of ether waves was shown to be expressed 
 by the equation 
 
 v = In 
 
 In order to obtain numerical values for these quantities, it is evident 
 that the value of v must be determined by reference to the best 
 available experimental data. Numerous investigators have agreed 
 upon 3 X10 10 centimeters per second as representing the most prob- 
 able value for this constant. Knowing this, and by assigning the 
 correct values to the factors capacity and inductance in determining 
 the natural frequency, it becomes a simple matter to calculate the 
 length of wave emitted by a radiator; and, conversely, by employ- 
 ing the proper capacity and inductance a radiator may be con- 
 
 21 
 
22 WIRELESS TELEGRAPHY 
 
 structed to give any desired wave-length within wide limits. Ca- 
 pacity and inductance may be considered to be the electrical dimen- 
 sions of an oscillator, and they determine the length of wave emitted, 
 just as the note emitted from an organ pipe depends upon the di- 
 mensions of such a pipe. 
 
 The waves created by Hertz with various forms of his oscillator 
 varied between a few inches and a few feet in length. He deter- 
 mined these lengths not only by mathematical computation as ex- 
 plained above, but by direct experimental test. He set up at the 
 far end of his laboratory a large sheet of metal to reflect back the 
 waves, and then went about the room with his resonator, exploring 
 the space to find at what points sparks were produced. He found 
 that when waves are thus reflected back upon themselves there are 
 nodal points, just as there are nodal points in sound-waves and in 
 light- waves when similarly reflected. Measuring the distances 
 between these nodal points he was able to determine the wave- 
 length precisely. 
 
 With the simple instruments at his command Hertz carried on 
 many other experiments which are little short of beautiful in their 
 adaptation of means to ends; but we cannot go into them here more 
 than to say that they all tended to prove the main contentions of 
 Maxwell's theory. The unqualified success of these experiments 
 won the admiration of scientists all over the world. But few, if 
 any, realized at the time that Hertz, in addition to giving indisputable 
 proof to Maxwell's famous hypothesis, had also laid the foundations 
 for a new and triumphant system of wireless telegraphy. 
 
 22 
 
CHAPTER III 
 THE DEVELOPMENT OF RADIOTELEQRAPHY 
 
 It is evident that when Hertz constructed an apparatus which 
 could transmit electrical manifestations to a distance, without wires, 
 he possessed the elements of a system of wireless telegraphy. All 
 signaling at a distance whether by wire or without, requires the 
 presence of three fundamental factors: a device to produce the 
 signal; a medium to carry the signal; and a device to receive the signal. 
 Hertz' apparatus with its oscillator, electromagnetic medium, and 
 resonator, easily fulfilled the requirements, and its use as a system 
 of wireless telegraphy was merely a matter of time. 
 
 The main line of development was to be an extension of the 
 distance over which signals could be transmitted; for as we have 
 seen in the consideration of earlier systems notably induction 
 systems distance is the important factor. Any system which can- 
 not transmit messages to a considerable distance is of small practical 
 service to the world. Hertz with his apparatus never succeeded in 
 producing waves which were detectable at more than a score of meters 
 or so; consequently we need not wonder that he never suspected that 
 one of the largest fruits of his achievement was to be a system of 
 wireless trans-oceanic communication. When asked by a civil 
 engineer of Munich whether he thought telephonic communication 
 could be effected by means of electric waves, he replied in the negative, 
 as he considered that the alternations of current in the telephone 
 were not of a nature to be detectable. He could not, of course, fore- 
 see the improvements which were destined to be made, rendering 
 his apparatus immeasurably more sensitive and serviceable. 
 
 All the scientists of Europe were stirred by the announcement 
 of Hertz' discoveries, and many set about to repeat the experi- 
 men'ts. With so many minds bent upon a kindred purpose it is not 
 surprising to learn that much new light was thrown upon the sub- 
 ject and many improvements made in the form and efficiency of the 
 Hertz apparatus. Both the radiator and the detector were signally 
 bettered. 
 
 23 
 
24 
 
 WIRELESS TELEGRAPHY 
 
 The Righi Oscillator. One of the disadvantages of Hertz* 
 radiator lay in the fact that the sparks in a short time oxidized the 
 little knobs and roughened their surfaces, resulting in irregular 
 action. Prof. Righi of Bologna overcame this difficulty by partly 
 enclosing two metal spheres, A and B in Fig. 10, in an oil-tight 
 case so that the outside hemispheres of each are exposed, the inner 
 hemispheres being immersed in vaseline oil with only a minute gap 
 between them. In a line with these spheres are ranged two smaller 
 spheres, C and D, which form the secondary terminals of the induc- 
 tion coil. Thus three sparks are produced: one between C and A, 
 another between A and J5, and another between B and D. It is 
 between A and B in the oil gap that the oscillatory spark takes place, 
 the other two sparks serving merely to charge the large spheres. 
 This arrangement not only produced a more constant spark by 
 preventing the pitting of the electrodes but greatly extended the 
 range of wave-lengths which it was possible to employ in investi- 
 gations of this character. The 
 dimensions of the oscillator could 
 thereby be reduced and the am- 
 plitude of the oscillations greatly 
 increased by reason of the fact 
 that higher potentials could be 
 reached before the energy was 
 released by discharge. Righi 
 obtained oscillations of a fre- 
 quency of 12,000,000,000 vibra- 
 tions per second by the use of 
 small spheres A and B eight 
 
 Fig. 10. Righi Oscillator . ir . ,. 
 
 millimeters in diameter. 
 
 The Branly Coherer. The next important advance pertained 
 to an improvement over the Hertz resonator as a means of detecting 
 electric waves. It was based on the discovery of M. E. Branly and 
 others, that the enormous resistance offered to the passage of an 
 electric current by powders and metal filings is greatly reduced under 
 the influence of electric oscillations. The resistance of such con- 
 ductors may drop instantly from thousands of ohms to hundreds 
 by the action of induced oscillations, retaining this conductivity 
 until "decohered" by a mechanical blow. It will be readily seen 
 
 24 
 
THE DEVELOPMENT OF RADIOTELEGRAPHY 25 
 
 that this provides a simple means of effecting the operation of a 
 translating device by acting as a valve in turning on, as it were, a 
 greater current in a local battery circuit. By utilizing this property 
 of increased conductivity Sir 
 Oliver Lodge succeeded in caus- 
 ing the deflection of a galva- 
 nometer. The device employed 
 by Lodge consisted of a glass 
 tube in the ends of which were 
 sealed terminal wires connected Fig n Lodge Coherer 
 
 to metallic electrodes of the 
 
 same diameter as the tube, and between the electrodes was placed a 
 small quantity of iron filings, as shown in Fig. 11. This device is 
 known as a coherer, a name suggested by Lodge. In various 
 modified forms the instrument has been employed up to the present 
 day in different wireless systems. Its practical application will be 
 fully considered later in connection with the work of Marconi. 
 
 Radiotelegraphy First Suggested. As the Righi oscillator and 
 Branly coherer were immeasurably more efficient than Hertz* cor- 
 responding apparatus, it necessarily follows that waves could be 
 sent and detected over much longer distances and the time was 
 getting ripe for the application of these devices to the purposes of 
 wireless telegraphy. The first man to suggest this possibility is 
 said to have been Sir Wm. Crookes, the eminent English chemist 
 and physicist. In a magazine article which appeared in 1892 he 
 made the following marvelous forecast of Radiotelegraphy: 
 
 Rays of light will not pierce through a wall, nor, as we know only too 
 well, through a London fog; but electrical vibrations of a yard or more in 
 wave-length will easily pierce such media, which to them will be transparent. 
 Here is revealed the bewildering possibility of telegraphy without wires, posts, 
 cables, or any of our costly appliances. Granted a few reasonable postulates, 
 the whole thing comes well within the realms of possible fulfillment. At 
 present experimentalists are able to generate electric waves of any desired 
 length, and to keep up a succession of such waves radiating into space in all 
 directions. It is possible, too, with some of these rays, if not with all, to 
 refract them through suitably shaped bodies acting as lenses, and so to direct 
 a sheaf of rays in a given direction. Also an experimentalist at a distance can 
 receive some, if not all, of these rays on a proper instrument, and by concerted 
 signals, messages in the Morse code can pass from one operator to another. 
 
 What remains to be discovered is firstly, simpler and more certain 
 means of generating electrical rays of any desired wave-length, from the 
 
26 WIRELESS TELEGRAPHY 
 
 shortest, say a few feet, which will easily pass through buildings and fogs, to 
 those long waves whose lengths are measured by tens, hundreds, and thou- 
 sands of miles; secondly, more delicate receivers which will respond to wave- 
 lengths between certain defined limits and be silent to all others; and thirdly, 
 means of darting the sheaf of rays in any desired direction, whether by lenses 
 or reflectors, by the help of which the sensitiveness of the receiver (apparently 
 the most difficult of the problems to be solved) would not need to be so delicate 
 as when the rays to be picked up are simply radiating into space, and fading 
 away according to the law of inverse squares. . . * 
 
 At first sight an objection to this plan would be its want of secrecy. 
 Assuming that the correspondents were a mile apart, the transmitter would 
 send the waves out in all directions, and it would, therefore, be possible for 
 anyone living within a mile of the sender to receive the communication. This 
 could be got over in two ways. If the exact position of both sending and 
 receiving instruments were known, the rays could be concentrated with more 
 or less exactness on the receiver. If, however, the sender and receiver were 
 moving about, so that the lens device could not be adopted, the correspondents 
 must attune their instruments to a definite wave-length, say, for example, 
 50 yards. I assume here that the progress of discovery would give instru- 
 ments capable of adjustment by turning a screw, or alternating the length of 
 a wire, so as to become receptive of waves of any preconcerted length. Thus, 
 when adjusted to 50-yard waves, the transmitter might emit, and the receiver 
 respond to, rays varying between 45 and 55 yards, and be silent to all others. 
 Considering that there would be the whole range of waves to choose from, 
 varying from a few feet to several thousand miles, there would be sufficient 
 secrecy, for the most inveterate curiosity would surely recoil from the task 
 of passing in review all the millions of possible wave-lengths, on the remote 
 chance of ultimately hitting on the particular wave-length employed by those 
 whose correspondence it was wished to tap. By coding the message even 
 this remote chance of surreptitious tapping could be rendered useless. 
 
 This is no mere dream of a visionary philosopher. All the requisites 
 needed to bring it within the grasp of daily life are well within the possibilities 
 of discovery, and are so reasonable and so clearly in the path of researches 
 which are now being actively prosecuted in every capital of Europe, that we 
 may any day expect to hear that they have emerged from the realms of specu- 
 lation into those of sober fact." . . . 
 
 The purposes and problems of radiotelegraphy are admirably 
 stated in the above. Some of those problems have not even yet 
 been solved, as we shall see. When Crookes wrote, the idea of 
 radiotelegraphy was in the air, and many men indeed were striving 
 to turn the possibility into a reality. Several Englishmen almost 
 achieved the desired end, but, strangely enough, faltered or failed 
 when success was within easy reach. Among these, mention must be 
 made of Prof. D. E. Hughes, who, but for a combination of bad 
 luck and human fallibility, might have been today the accredited 
 discoverer not only of radiotelegraphy but of electric waves as well. 
 
 26 
 
THE DEVELOPMENT OF RADIOTELEGRAPHY 27 
 
 Work of Hughes. As far back as 1879, when experimenting 
 with his celebrated microphone (which is in reality nothing other 
 than a Branly coherer reduced to its simplest elements) Hughes 
 observed peculiar electrical effects operating at a distance, and he 
 concluded that they were due to invisible electric waves. He did 
 not, however, so far as we know, relate these phenomena with the 
 theories of Maxwell, as Hertz did, and was consequently at a loss 
 to fully account for them. He investigated the subject for several 
 years and actually succeeded in telephoning wirelessly over consider- 
 able distances. These experiments were repeated before Prof. Stokes, 
 the president of the Royal Society, and Prof. Huxley; but these 
 gentlemen expressed doubts as to the nature of the phenomena, 
 with the result that Hughes became infected with their scepticism 
 and abandoned his efforts, believing himself on the wrong track. If 
 he had persisted in his researches he might have gathered the laurels 
 that later went to Hertz and Marconi. It has been said that "Hughes' 
 experiments of 1879 were virtually a discovery of Hertzian waves 
 before Hertz, of the coherer before Branly, and of wireless telegraphy 
 before Marconi and others," and the truth of the statement must 
 be admitted to some extent. 
 
 Work of Lodge. Mention must be made of the great debt which 
 radiotelegraphy owes to Sir Oliver Lodge for his many valuable 
 contributions both to practice and theory. He has been in the fore- 
 front of every advance made in the science of radiotelegraphy, and 
 might in all truth be called its patron saint. To him is due our 
 knowledge of the principles of syntony which forms such a vital 
 part of all modern systems. He was the first man to employ the 
 Branly coherer as a detector of Hertzian waves, and while engaged 
 in demonstrating the discoveries of Hertz was sending signals over 
 distances measurable in hundreds of feet. That such signals could 
 be utilized to convey intelligence by the simple application of the 
 Morse telegraphic code did not occur to him; if he had realized this 
 possibility he might have antedated Marconi's invention of wireless 
 telegraphy. 
 
 Work of Marconi. Passing over Popoff, Rutherford, Jackson, 
 Minchin, and others, several of whom did important and original 
 work, we come to Marconi who, in the popular mind, is credited 
 with the whole achievement of radiotelegraphy. It is true that 
 
 27 
 
28 
 
 WIRELESS TELEGRAPHY 
 
 Marconi carried radiotelegraphy through to practical success; or, 
 as A. T. Story puts it, "he carried forward into the domain of 
 practical reality what had only floated indistinctly before the minds 
 of others, or had served them for modest experiments." But as 
 regards those vital arid fundamental developments of theory and 
 practice without which radiotelegraphy would still be a thing un- 
 known, Marconi is only an able follower and not one of the pioneers. 
 The history of radiotelegraphy might be shortly indicated by the 
 following list of names: Faraday, Maxwell, Hertz, Righi, Lodge, 
 Marconi. The theory of electric waves originating with Faraday 
 and expanded by Maxwell, was experimentally demonstrated by 
 Hertz. Then came Righi and Lodge with their improvements on 
 
 the Hertz apparatus, greatly ex- 
 tending its sphere of utility; and 
 finally Marconi, who brought to- 
 gether the results achieved by his 
 predecessors and, adding some- 
 thing of his own "a far-seeing 
 initiative where others had not 
 gone beyond timid projects or 
 tentative research" produced a 
 successful system of wireless teleg- 
 raphy. Marconi, who is an 
 Italian by birth, first became 
 interested in Hertzian waves when 
 a student under Prof. Righi at 
 
 the Bologna University. He was not long in seeing their possible 
 application to telegraphy, and made some experiments with that 
 purpose in view. Becoming convinced of the feasibility of the 
 project, but finding no one in Italy ready to take it up, he set 
 out for England to try his fortune. Arriving there, he applied 
 to the Patent Office for protection on his ideas, and then took 
 the proposition to Sir Wm. Preece, chief of the British Postal 
 Telegraphs. Preece gave Marconi ready encouragement, and he 
 was soon conducting experiments under the auspices of the British 
 Post Office. 
 
 Early Apparatus. The early apparatus of Marconi consisted es- 
 sentially of a Righi oscillator and Branly coherer, disposed in suitable 
 
 Fig. 12. Early Marconi Transmitter 
 Circuit 
 
 28 
 
THE DEVELOPMENT OF RADIOTELEGKAPHY 29 
 
 circuits for generating and recording the flow of waves. The trans- 
 mitting arrangement consisted of an induction coil producing the 
 requisite high potential with which to charge a Righi oscillator, 
 and a Morse key of heavy construction with which to break the 
 primary circuit of the coil, connected with a battery of about five 
 cells. The actual transmission of messages was effected by the 
 intermittent movement of the Morse key which, upon completing 
 the circuit, started the interrupter of the coil which remained in 
 
 Fig. 13. Early Marconi Receiving Circuit 
 
 operation as long as the key was held down; thus the duration of 
 waves from the oscillator was made dependent on the position of 
 the key. It was thus possible by the proper manipulation of the 
 key to send a series of long or short wave trains corresponding to the 
 dots and dashes of the Morse alphabet. Fig. 12 represents dia- 
 grammatically these features of the sending station. 
 
 The receiving apparatus, indicated in Fig. 13, consisted prin- 
 cipally of the Branly coherer somewhat modified in construction 
 and associated with suitable auxiliary apparatus for recording the 
 duration of the received wave trains in the form of dots and dashes 
 
 29 
 
30 
 
 WIRELESS TELEGRAPHY 
 
 upon a moving paper surface after the manner of the Morse recorder, 
 well known in wire telegraphy. As the coherer retains its low con- 
 ductivity even after the cessation of a train of waves, it becomes 
 necessary to provide means for automatically imparting a slight 
 blow or jar to the tube in order to restore its receptiveness after 
 each and every signal. Such a device was used by Lodge and is 
 known as a "tapper." It is generally in the form of an electric 
 trembling mechanism, such as an electric bell, operated by a local 
 battery when thrown into the circuit by a Morse relay the latter 
 acting in response to the increase of current when the coherer acts. 
 The coherer used by Marconi at this time was his own special 
 modification of the Branly-Lodge type. It consisted of a glass tube 
 
 Fig. 14. Marconi "Capacity Areas" 
 
 about 4 centimeters long and 2.5 millimeters in diameter, into which 
 were tightly fitted two silver terminals separated to a distance of one 
 millimeter, this space being filled with a powdered mixture of 96 
 parts nickel to 4 parts silver, worked up with a trace of mercury. 
 The tube was exhausted of air and hermetically sealed. To the 
 terminals of this coherer were connected two resonance plates, or 
 strips of copper, whose dimensions were such as to bring the system 
 into resonance with the oscillator. Also connected to the terminals 
 of the coherer were two choke coils, whose function was to confine 
 the oscillations to the coherer; and a Morse relay in series with a 
 battery of one cell. Fig. 13 plainly shows the arrangement. 
 
 30 
 
THE DEVELOPMENT OF RADIOTELEGRAPHY 31 
 
 In addition to the above a tapper was provided to decohere 
 the metal filings, and also a signal recorder. The tapper was in 
 the form of a small electric-bell mechanism whose clapper con- 
 tinuously tapped the glass tube as long as the Morse relay com- 
 pleted the circuit in which the tapper was placed. The Morse relay 
 thus acts as a switch by means of which the signal recorder and 
 tapper are operated simultaneously. It might be well to state that 
 the coherer holds its conductivity during the passage of the oscilla- 
 tions even though in vibration from the tapper. 
 
 Capacity Areas. A very significant step taken by Marconi at 
 this early period was his employment of "capacity areas" in the 
 circuit of his oscillator, Fig. 14. 
 The essential features of this in- 
 novation were as follows : T and 
 T are metal plates joined to the 
 balls of the oscillator; C is the 
 induction coil. The object of 
 this arrangement was to give 
 greater energy to the oscilla- 
 tions, the carrying power of the 
 apparatus being found to in- 
 crease with the size of the capac- 
 ity areas, and with the distance 
 of the same from each other. 
 Two similar plates were also 
 attached to the coherer at the 
 receiving station. Though this 
 arrangement of capacity areas 
 was soon abandoned, it marks, 
 nevertheless, the inception of an 
 idea which developed, as we 
 shall see, into one of the most 
 important features of modern aerial telegraphy, namely, the antenna. 
 
 Development of the Antennae. Endeavoring to increase the 
 effectiveness of his capacity areas by enlarging them and separating 
 them as much as possible, Marconi conceived the idea of utilizing 
 the earth for one of the plates, and of raising the remaining plate to 
 a considerable height in order to increase the distance between them. 
 
 Fig. 15. Diagram Showing the 
 Earthed Oscillator 
 
 81 
 
32 
 
 WIRELESS TELEGRAPHY 
 
 &4PAC/TY 
 AREA 
 
 The arrangement, Fig. 15, then took on the following aspect: coil 
 and oscillator are of standard type; E is the earth connection; 
 and W the elevated plate. The higher the capacity area W is 
 situated, the greater the distance to which communication can be 
 carried; so it will be seen that the capacity area might with great 
 advantage be attached to a kite, or captive balloon. The latter 
 were, indeed, employed by Marconi and with very good effect. 
 
 Corresponding changes were made 
 at the receiving station also, by 
 employing a similar arrangement 
 of capacity area, shown in Fig. 16. 
 Later Marconi became con- 
 vinced that the effectiveness of 
 his aerial line was due not to the 
 capacity at the end of the wire, 
 but to the length of the wire itself; 
 consequently he abandoned the 
 capacity area altogether and held 
 simply to the form of vertical 
 wires attached to poles or kites, 
 or even to high buildings or 
 towers. These were called an- 
 tennae, or aerials. The antenna 
 consisting of a single wire later 
 developed into the multiple an- 
 tenna of several wires, each ad- 
 ditional wire adding to the capac- 
 ity of the system. The antennae 
 
 of many large stations are formidable structures of great complexity, 
 as the picture of the South Wellfleet station, Fig. 17, will indicate. 
 Inductive Receiving Antennae. Another of Marconi's early 
 and important modifications was the introduction of inductive an- 
 tennae into the receiver arrangement. The antenna was cut out of 
 direct conductive connection with the coherer circuit and allowed to 
 act on the latter only by induction through the agency of an oscilla- 
 tion transformer called in common parlance a jigger, the theory of 
 which cannot be fully discussed here. Mention will be made, how- 
 ever, of the fact that such a transformer properly designed in regard 
 
 EARTH 
 Fig. 16. Earthed Receiving Circuit 
 
THE DEVELOPMENT OF RADIOTELEGRAPHY 33 
 
 to the wave-length used not only steps up the voltage so as to increase 
 its effect on the coherer, but also enables the coherer to be placed at 
 a nodal point of the secondary oscillations. As this form of detector 
 
 Fig. 17. South Wellfleet Wireless Station 
 
 is of the potentially operated variety, the practical importance of 
 the modification is apparent. A coherer placed in series between 
 the antennae and ground, as in former arrangements, is poorly located, 
 as at the base of an aerial the potential is a minimum and the current 
 a maximum. Marconi increased the distance over which it was 
 possible to signal nearly ten times by the employment of this simple 
 
 SECONDARY* 
 
 AX/S 
 
 _ GLASS .TUBE __ 
 
 Fig. 18. Diagram of Oscillation Transformer Winding 
 
 device. His patents on this improvement bear the dates of 1898 
 and 1899. Fig. 18 shows a diagrammatic cross-section of the jigger, 
 the zigzag lines representing the successive layers of the windings 
 wound in such a manner that the inner layers have the greatest num- 
 
 33 
 
34 
 
 WIRELESS TELEGRAPHY 
 
 ber of turns, the primary having about 100 and the secondary about 
 1,000 turns. Fig. 19 shows the receiver-circuit with the jigger em- 
 bodied therein. It will be noticed that the local-battery circuits are 
 the same as used before, but the jigger necessitates a slight modifica- 
 tion in the location of the coherer. A condenser is connected to the 
 inner terminals of the secondary, the outer terminals of which are 
 connected to the coherer. The local battery circuit is also con- 
 nected to the inner ends of the secondary and across the condenser. 
 Inductive Transmitting Antennae. It has already been shown 
 that the early capacity areas had given place to the extended wire 
 raised to a great height; and it soon became evident that transmission 
 
 could be further facilitated by 
 devising a more persistent oscil- 
 lator than that which was em- 
 ployed with the directly connected 
 aerial. It was possible to store 
 a fair amount of energy in the 
 old type of aerial, but the direct 
 connection entailed the disadvan- 
 tage 0f permitting the apparatus 
 to radiate its entire amount of 
 energy almost instantly instead 
 of radiating such energy in the 
 form of "a more continuous train. 
 This was not a quality tending to 
 make for a clearly defined reso- 
 nance between the sending and 
 receiving circuits, and means were 
 sought to accomplish a more per- 
 sistent, or less damped, series of oscillations. The early form of open- 
 circuit oscillator, therefore, gave place to what is known as the Marconi- 
 Braun type of closed oscillating circuit which, while not so powerful a 
 radiator, was a very much more persistent one. The method was due 
 to Prof. Braun, but in a ^modified form was first used by Marconi. 
 The diagram of Fig. 20 makes clear the fundamental idea, an idea 
 which has proven to be- of great value. Though modified in number- 
 less ways by subsequent inventors, the broad idea of associating the 
 aerial with a closed oscillating circuit has become almost universal. 
 
 vwwvwv 
 
 SECONDARY 
 
 Fig. 19. Marconi Receiver-Circuit with 
 Jigger 
 
 34 
 
THE DEVELOPMENT OF RADIOTELEGRAPHY 
 
 35 
 
 CONDENSE* 
 
 The transformer used for this purpose is very different from 
 the ordinary induction coil or alternating-current transformer em- 
 ployed in connection with low voltages and low frequencies. It will 
 be fully described later under the head of oscillation transformers; 
 for the present it is sufficient to say that it forms an inductive couple 
 between the two oscillatory circuits, the closed circuit being but a 
 means of charging the open circuit of the antennae. The antennae 
 circuit, having a certain amount 
 
 of capacity and inductance de- AER/AL 
 
 pending on its design and posi- 
 tion, possesses a natural time- 
 period of its own; so in order to 
 induce in such a circuit oscilla- 
 tions of a maximum amplitude, 
 the primary circuit associated 
 therewith must have the same 
 natural time-period. In other 
 words, resonance must be estab- 
 lished; two circuits, as before 
 mentioned, being in resonance 
 when the product of capacity and 
 inductance is the same for both. 
 The Marconi-Braun method of 
 charging the aerial permits of the 
 employment of very large capaci- 
 ties, with proportionally larger 
 energy-storing ability and smaller Fi s 20 
 inductances in the primary circuit, 
 so that the product of these two factors can be made to equal the 
 product of the corresponding factors in the antenna circuit. The 
 efficiency of the transformer thus very largely depends on the estab- 
 lishment of syntony between the closed oscillatory circuit forming the 
 primary and the open oscillatory circuit forming the secondary. 
 
 Another method of associating the radiating aerial with a closed 
 oscillatory circuit, possessing many of the advantages of the Marconi- 
 Braun inductive couple, is shown in Fig. 21, and is known as the 
 direct-coupling method. An inductance of several turns of wire is, 
 in effect, introduced in series with the aerial and the ground. A 
 
 Marconi-Braun Inductive Trans- 
 mitting Antennae 
 
 35 
 
36 
 
 WIRELESS TELEGRAPHY 
 
 AERIAL 
 
 CONDEN, 
 
 certain portion of the inductive turns is included in a closed oscilla- 
 tory circuit composed of a condenser and spark gap shunted around 
 the said portion. When the closed energy-storing oscillatory cir- 
 cuit and the open radiating circuit of the aerial are adjusted to the 
 same periodicity the scheme becomes effective. The method of 
 direct coupling has been subjected to many changes at the hands 
 of inventors, in some cases becoming almost unrecognizable, but upon 
 
 analysis the fundamental idea 
 shows through. It is to be noted 
 that with both the direct and 
 inductively coupled systems, syn- 
 tony between the open and closed 
 circuits is essential. 
 
 Both of the foregoing ar- 
 rangements allow the possibility 
 of creating in the aerial far great- 
 er charging electromotive forces 
 which, in properly proportioned 
 antennae, increase toward the 
 top where they may reach a value 
 equivalent to hundreds of thou- 
 sands of volts in the larger in- 
 stallations. Hence, with the 
 adoption of this form of trans- 
 mitting arrangement, it became 
 possible to radiate a series of well- 
 sustained oscillations of much 
 greater energy than ever before, 
 
 thus still farther extending the distance to which communication 
 could be carried. This improvement may be said to be one of the 
 greatest advances in the history of radiotelegraphy. 
 
 Propagation of Waves from a Grounded Oscillator. The theory 
 of the propagation of electric waves from a Hertz oscillator before 
 given, assumed a perfectly symmetrical isolated oscillator suspended 
 in space. The employment of the grounded oscillator in the form 
 of an earthed aerial now exclusively used in radiotelegraphy neces- 
 sitates a modification of the above theory in order to meet the prob- 
 lems arising under the changed conditions. The new arrange- 
 
 Fig. 21. 
 
 "Direct-Coupled" Inductive 
 Antennae 
 
 36 
 
THE DEVELOPMENT OF RADIOTELEGRAPHY 37 
 
 ment was, in effect, the substitution of the earth for one of the capacity 
 areas of a Hertz radiator, and the extension of the companion area 
 into a vertical wire possessing capacity with regard to the earth from 
 which it is separated by an air gap. The type of wave radiating 
 from such a system differs in many respects from the form of dis- 
 turbance emanating from a simple isolated oscillator, and presents 
 theoretical difficulties which cannot as yet be said to be satisfactorily 
 explained. The electric waves from a grounded oscillator apparently 
 follow the curvature of the earth. One of the theories purporting 
 
 Fig. 22. Diagrammatic Representation of the Sliding- Wave Theory of Propagation 
 
 to account for this phenomenon assumes that such waves are not 
 ordinary free electric waves consisting of closed loops of electric 
 strain, but on the contrary consist of half loops traveling over the 
 surface of our globe with their ends remaining always in contact with 
 the surface. This view is supported, it would seem, by the electronic 
 theory of electricity. It is roughly represented in Fig. 22. The 
 detached semi-loops of strain are shown by the lighter lines, and 
 the simple grounded oscillator by the heavier. A wave-length would 
 be represented on the horizontal line by the distance included be- 
 tween any two positions thereon where the direction and intensity 
 of strain (shown respectively by the arrows and the proximity of 
 the lines) is identical. This is the sliding-wave theory, said to have 
 
 37 
 
38 WIRELESS TELEGRAPHY 
 
 been first promulgated by J. E. Taylor. Other theories have been 
 advanced to account for the wave-transmission following the curva- 
 ture of the earth, one such assuming that the waves are radiated in 
 a straight line but reflected back from a semi-conductive envelope 
 formed by the upper strata of the earth's atmosphere. 
 
 Selective Signaling. The problem of directing a message to 
 its proper destination was felt by early investigators to be of vital 
 importance, if radiotelegraphy was ever to be a commercial success. 
 Some method must be discovered to effect selective signaling else 
 how would it be possible for a plurality of stations to be transmitting 
 at once? The solution of the difficulty was thought to be found in 
 the principle of resonance. 
 
 The history of the subject records at a very early date efforts 
 to achieve the desired end by employing definite wave-lengths corre- 
 sponding to the electrical time-periods of the various stations it was 
 desired to place into communication. Thus among a plurality of 
 active sending stations any number might communicate simultane- 
 ously in pairs without interference by arbitrarily assigning a definite 
 frequency, or wave-length, to each pair. Selection by this method 
 assumes that it is possible to "tune" receiving instruments so they 
 will respond to a particular "pitch" and to no other; but as the num- 
 ber of possible non-interfering wave-lengths is limited, it cannot be 
 said that resonance offers an entirely satisfactory solution of the 
 problem. 
 
 By the employment of two or more receiving circuits connected 
 to the same aerial, each tuned to a different frequency correspond- 
 ing to as many different sending stations, the simultaneous recep- 
 tion of two or more messages is theoretically possible. As early as 
 1900, Marconi achieved some very remarkable results of simultaneous 
 non-interfering communication when he received by the same aerial 
 two messages, one in English and the other in French, which were 
 simultaneously transmitted over a distance of 30 miles. 
 
 It was to be expected that the last few years would bring in their 
 train great improvements in this respect as well as in others, so that 
 it may be said today that selective signaling is feasible to a certain 
 extent and that the remaining obstacles will be* removed by further 
 developments of the art; but until those advances are made, so that 
 much more can be accomplished with respect to selective signaling 
 
THE DEVELOPMENT OF RADIOTELEGRAPHY 39 
 
 than at present, the field of operation for radiotelegraphy will be 
 confined mostly to communication between ships, between ships 
 arid shore, and across large bodies of water. 
 
 Conclusion. The application of Hertzian waves to the pur- 
 poses of telegraphy as outlined above, covers what might be called 
 the foundation and early development of the art. Every step taken 
 at this early period was vital and significant. Since then enormous 
 advances have been made; the distances over which it is possible to 
 telegraph have been greatly extended, and the apparatus rendered 
 more sensitive and certain in every way; but these results have been 
 accomplished more by a refinement of detail the development of 
 more sensitive instruments, and the closer connection between theory 
 and practice rather than by the application of fundamentally new 
 ideas. The twentieth century ushered in a new and tentative method 
 of telegraphic communication called radiotelegraphy, and the first 
 ten years have witnessed its establishment as one of the permanent 
 adjuncts of civilization, 
 
 39 
 
CHAPTER IV 
 RADIOTELEGRAPHIC APPARATUS 
 
 It is obviously impossible within the scope of the present work 
 to give a detailed description of all the apparatus pertaining to 
 radiotelegraphy. In view thereof it is assumed that the reader is 
 familiar with the ordinary instruments and physical appliances 
 commonly used in electrical work and not in any way peculiar to 
 wireless telegraphy. It is also assumed that the elementary facts of 
 electrical phenomena are known. The descriptions of the apparatus 
 in this chapter will be given without reference to their grouping to- 
 gether in the formation of a complete system, but will be given 
 singly with such theoretical considerations as may seem necessary. 
 The chapter following will be given over to the assembling of apparatus 
 into complete systems under their proper appellations, together with 
 some account of their performance. fc> 
 
 Sources of Energy. In any system of radiotelegraphy the prime 
 desideratum is to associate with the aerial a maximum amount of 
 energy available for radiation. It was early recognized that the 
 most obvious way to accomplish this was to increase the capacity 
 of the aerial or to employ condensers associated in various ways in 
 order to store temporarily the electrical energy to be radiated. The 
 main function, therefore, of the source of energy employed in the trans- 
 mitting station is to properly charge a given capacity. The greater 
 this capacity, the greater the amount of initial energy required. 
 Expediency determines largely the nature of the source of energy, 
 whether derived from storage batteries, a generator, or from power 
 mains. The energy consumption ranges from a few watts up to 
 50 to 100 kilowatts, so it is evident that the sources of current are 
 subject to a wide range of choice. The trans-Atlantic stations of 
 Marconi at Cape Breton employ generators of 65 horse-power. 
 
 Charging Devices. To create the required electrical oscillations 
 in the aerial, it is necessary to have appliances which shall generate 
 the requisite high-potential electromotive forces for charging the 
 
 40 
 
RADIOTELEGRAPHIC APPARATUS 41 
 
 aerial and its associated capacity. Such an appliance should create 
 not only a high potential but also an appreciable current. This 
 charging e. m. f. is generally effected by the use of the induction coil 
 or the alternating-current transformer. 
 
 Induction Coils. It is not deemed necessary to give an extended 
 discussion of the induction coil, but to call attention to the important 
 modifications to be incorporated therein for use in wireless telegraphy. 
 The purpose for which the coil is employed is to charge a condenser 
 of some form rapidly. The time required for a condenser to attain 
 the same potential as the charging source to which it is connected 
 depends largely upon the resistance of the charging source. In 
 order to secure a small time-constant for the charging circuit, it is 
 highly desirable to have a secondary of as low resistance as possible. 
 The lower the resistance of the secondary, the greater the capacity 
 that can be rapidly charged by a coil of a given number of turns. 
 It must be borne in mind that, in order to charge a condenser to a 
 given potential, current is required. The usual small induction coil 
 is wound with very fine wire on the secondary No. 36 or finer. It 
 goes without saying that this is not at all suited for use in wireless 
 telegraphy. Considerable data on coils suitable for the use herein 
 considered is available. The core should be composed of well- 
 annealed, Swedish soft iron wire of small diameter about No. 24 
 wound with a primary of comparatively few turns of coarse copper 
 wire about No. 12 double cotton-covered and well insulated from 
 the core. It is not practical to wind the secondary with coarser wire 
 than No. 32 or No. 33 B. & S. gauge. Special attention should be 
 paid to the insulation of the secondary as it is of great importance 
 that this be able to withstand the high impulsive electromotive forces 
 of short duration which occasionally manifest themselves. Late de- 
 sign seems to be in the direction of longer cores about twice the 
 length of the secondary winding. 
 
 Tesla called attention to a fact of importance in connection 
 with induction-coil design, as far back as 1893, viz, that a condition 
 of resonance between the primary and the secondary circuits greatly 
 adds to the efficiency of the device. This has the practical result 
 of greatly decreasing the resistance of the secondary and also the 
 number of turns, with a result that much more current is deliverable 
 from such a coil. In the primary circuit there is usually large capacity 
 
 41 
 
42 
 
 WIRELESS TELEGRAPHY 
 
 SPARK GAP 
 
 COKS 
 
 and small inductance, while in the secondary there is small capacity 
 and large inductance. 
 
 Even with the above added efficiency, induction coils are not 
 as suitable in many respects for commercial radiotelegraphy as 
 alternating-current transformers. The utility of the induction coil 
 is limited by reason of the fact that the details of design are so largely 
 a matter of compromise that it is impracticable to obtain the desired 
 charging current at the required voltage. The efficiency of induction 
 coils is at best but slightly above 50 per cent, and there are reasons 
 for believing it much lower. 
 
 The three important adjuncts of the induction coil are the pri- 
 mary condenser, the interrupter, and the signaling key. 
 
 Primary Condenser. The principal function of the primary 
 condenser is to absorb the energy that manifests itself at break in 
 
 the form of an arc, due to the 
 self-induction of the primary cir- 
 cuit. As the secondary e. m. f. 
 is due largely to the suddenness 
 of the rupture in the primary, it 
 is qf the utmost importance that 
 this arc be prevented from form- 
 ing. The primary condenser is, 
 therefore, placed across the break 
 j n Suc j 1 a manner as t k e short- 
 
 circuited when the circuit 
 
 s 
 
 closed, but at the instant of 
 break it is placed in the circuit 
 
 and absorbs the energy which would otherwise be dissipated in 
 the formation of an arc, and which would very greatly increase the 
 time of rupture. Fig. 23 indicates the arrangement of the circuit. 
 The best value for the primary condenser is that capacity which 
 will annul to the greatest degree the sparking at the points of the 
 interrupter. Experiments have shown that if the primary be broken 
 with sufficient rapidity, as for instance with a rifle ball, no condenser 
 is needed. A condenser is not needed with a Wehnelt interrupter. 
 
 Interrupters. Interrupters perform the sole function of causing 
 a rapid succession of sudden breaks in- the primary circuit. The 
 commonest as well as the oldest form of break is known as the hammer 
 
 Fig. 23. Diagram of Induction Coil 
 Showing Condenser Circuit 
 
RADIOTELEGRAPHIC APPARATUS 
 
 43 
 
 break, probably invented by Neef. Its action is perhaps best shown 
 by referring to the common electric door-bell. An electromagnet, 
 in attracting an armature, causes 
 an interruption of the current 
 energizing the electromagnet, 
 whereupon the armature falls 
 back by reason of its spring 
 tension and again completes the 
 circuit; this energizes the magnet 
 once more, which again attracts 
 the armature, and the whole 
 operation is repeated. The arm- 
 ature is thus kept in continual 
 vibration with consequent inter- 
 ruptions of the current. Fig. 24 
 shows this device which is sub- 
 ject to almost endless variation 
 
 in a form having as one of 
 its decided advantages the ease 
 with which it is adjusted by 
 
 simple regulation for different frequencies. Fig. 25 shows an- 
 other form with the contacts made in small cups of mercury, known 
 as the Foucault break. It is obvious that the break can be 
 produced independently of the 
 current in the primary circuit 
 by means of a small electric 
 motor acting on a lever which is 
 made to dip into a cup of mer- 
 cury, thus completing the circuit 
 any desired number of times per 
 revolution. Such a break is 
 called the motor break. The 
 rotary, or turbine, break has 
 been used very successfully on 
 large coils requiring considerable 
 amperage for their operation. The simple hammer break does 
 not operate well with voltages over 16 or 20; therefore, when it be- 
 comes necessary to utilize commercial pressures such as 110 and 
 
 Fig. 24. Neef Hammer Break 
 
 Fig. 25. Foucault Mercury Break 
 
 43 
 
44 
 
 WIRELESS TELEGRAPHY 
 
 220 volts, some form of mercury turbine interrupter is found to be 
 preferable. One form of this interrupter is shown in Fig. 26. 
 
 Dr. Wehnelt of Charlottenburg invented, in 1899, a form of 
 interrupter for use with induction coils, operating on an entirely 
 different principle from those described above. Taking two elec- 
 trodes of very different size, such as a large lead plate and a small 
 piece of platinum wire projecting from the end of a closely fitting 
 glass tube, and placing them in an electrolyte of dilute sulphuric 
 acid, he discovered that an electrolytic action takes place when the 
 
 Fig. 26. Mercury Turbine Interrupter 
 
 large lead plate is made the negative pole, this action interrupting 
 the current periodically when the device is connected to a source of 
 40 to 80 volts. Fig. 27 gives an idea of the device, showing one of 
 the many modifications it has undergone in its commercial design. 
 The positive platinum electrode can be seen protruding slightly from 
 the end of the porcelain insulating tube immersed in the liquid, which 
 must be a solution of about one part sulphuric acid to ten parts of 
 
 44 
 
RADIOTELEGRAPHIC APPARATUS 
 
 45 
 
 water. The cut shows a water-cooling jacket, which is an advantage 
 as the apparatus becomes very warm under continued use. Ex- 
 periments have shown this device to be capable of producing an in- 
 termittency of over 1,800 per second. As mentioned above, no con- 
 denser is necessary when opera- 
 ting an induction coil with this 
 form of interrupter. The char- 
 acter of the secondary discharge 
 is somewhat changed by the use 
 of the Wehnelt cell, rendering it 
 more like the alternating arc than 
 the usual disruptive spark. It 
 cannot be said that an entirely 
 satisfactory theory has ever been 
 given for the action of this cell. 
 The Wehnelt interrupter has not 
 been used very commonly in 
 connection with radiotelegraphic 
 work, its greatest field of useful- 
 ness being in Rontgen ray work. 
 
 Keys. In order to transmit messages by means of an arbitrary 
 code consisting of long and short trains of waves representing the 
 Morse alphabet, an adequate means of controlling the torrent of 
 sparks between the electrodes of the spark gap must be employed. 
 The key problem in this form of telegraphy is somewhat more com- 
 plicated than in the ordinary wire systems, primarily by reason of 
 the fact that a much greater current must be controlled. The com- 
 mon Morse key need not open more than a fraction of an inch, ^ T 
 being ample; but it becomes necessary in wireless work to rapidly 
 break currents of several amperes in circuits of considerable inductance, 
 under which conditions the Morse key would not answer at all. 
 The speed of signaling depends largely on the rapidity of the key, 
 a wide movement greatly cutting down the efficiency of the system 
 as a means of communication; therefore, short-range keys must be 
 provided, with some means of annulling the heavy spark on break. 
 Many suggestions have been made and a number of patents taken 
 out purporting to accomplish this end. The magnetic blow-out has 
 proved the most generally useful; though some systems employ a 
 
 Fig. 27. Wehnelt Interrupter 
 
 45 
 
46 
 
 WIRELESS TELEGRAPHY 
 
 short-circuiting resistance around the break, and others a condenser 
 to absorb the arc. One form of Marconi key simultaneously breaks 
 the primary current and disconnects the aerial from the transmitting 
 
 apparatus. Many keys are de- 
 signed to cause the break to 
 take place under oil or other 
 highly insulative substances. 
 Lodge and Muirhead employ an 
 electromagnetically operable key 
 which is actuated by current in 
 a local circuit interrupted by an 
 ordinary Morse key. A common 
 form of such a key, which is of 
 
 Fig. 28. Long Range Morse Key yery heayy construc tio n and of 
 
 extra wide movement, is shown in Fig. 28. 
 
 Alternating=Current Transformers. In nearly all high-power 
 stations it has been found advantageous, if not absolutely necessary, 
 to discard the induction coil as a means of charging the high capacities 
 used, substituting the alternating-current transformer, This in- 
 volves the employment of an alternating-current as the initial source 
 of power. Transformers designed for this purpose are wound for 
 a high ratio of transformation, generally for a secondary voltage of 
 at least 20,000 volts, and often 30,000 to 50,000. A difficulty expe- 
 rienced with the use of the transformer 
 is the liability of forming an alternating 
 arc between the balls of the gap in place 
 of the proper oscillatory spark. The 
 practical short-circuiting of the trans- 
 former by this action causes a great rush 
 of current through the primary, which, 
 if it has not been guarded against, is 
 liable to cause great havoc with the gen- 
 erator, blowing out the fuses and possi- 
 bly working other damage more serious. 
 When the capacity of the condenser 
 
 is of the exact value to take up in the form of a charge nearly the 
 entire energy of each half-wave of the periodic current, no alternating 
 arc will arise and the discharge across the gap will be due entirely to 
 
 Fig. 29. Tesla Magnetic 
 Blow-out 
 
 46 
 
RADIOTELEGRAPHIC APPARATUS 47 
 
 the condenser, in which case no external means for extinguishing the 
 arc are necessary; but this relation is very hard to effect permanently, 
 so that numerous plans have been devised to prevent the formation 
 of this arc. The one due to Nikola Tesla, which has undoubtedly 
 proved to be the best, utilizes a strong electromagnet so that its lines 
 of force pass transversely between the spark gap. This arrange- 
 ment is called a magnetic blow-out. Fig. 29 shows the scheme. 
 Elihu Thomson achieves the same end by directing a strong blast 
 of air on the gap from a nozzle. This permits the oscillatory spark 
 to form at the proper time, but completely extinguishes the alter- 
 nating arc, or rather prevents its formation. The noise incident 
 to the operation of a large transformer producing a heavy oscillatory 
 spark is deafening and some precaution must be taken to protect 
 the ears of an attendant if the gap is not enclosed. The light from 
 such a spark is also very hard on the eyes. 
 
 Oscillation Transformers. Transformers designed for high- 
 frequency, high-potential, oscillatory currents are in many respects 
 different from the transformers suitable for use on low-pressure, 
 low-frequency, electric-light mains. The most striking difference 
 is the absence of an iron core and the small number of turns of wire 
 employed. The transformer used by Marconi with the Marconi- 
 Braun type of closed oscillator was constructed as follows: The 
 primary consisted of but one turn on a stranded conductor of low 
 resistance with a secondary of thinner wire laid over the primary in 
 about ten turns. The coils w T ere immersed in highly insulating oil. 
 In commercial practice oscillation transformers are of various design. 
 It is of the utmost importance that transformers of this character be 
 specially well insulated, particularly when the primary and the 
 secondary are in close inductive relation. The use of oil in this con- 
 nection is the common practice. Late forms of oscillation trans- 
 formers are made in such a manner that the distance between the 
 primary and the secondary may be varied, thus alternating their 
 inductive relation, a so-called "loose couple" being produced by 
 separating the two components. 
 
 Condensers. The condensers employed in radiotelegraphy, 
 as in other departments of electro-technics, are chosen with regard 
 to the voltages to which they are to be subjected. The capacity used 
 in connection with receiving circuits requiring no high insulating 
 
 47 
 
48 WIRELESS TELEGRAPHY 
 
 properties generally takes the form of paper or mica condenser sup- 
 plemented by a variable-capacity condenser consisting of a number 
 of fixed metallic plates interspaced in air between an equal number 
 of moveable plates, whereby the effective capacity areas of the plates 
 may be varied within wide limits. 
 
 In the transmitting circuit where the condenser is employed to 
 temporarily store the energy preparatory to the sending of a signal, 
 a form of condenser must be used which will withstand the electro- 
 static strain of a very high potential. This necessitates the use of 
 glass, mica, or oil, as experience has proved these materials to be 
 almost the only dielectrics practicable for the purpose, glass being, 
 all things considered, the best of all. The higher the voltage, the 
 greater the thickness of glass needed; and as the storing power of a 
 
 ^ 
 
 Fig. 30. Adjustable Condenser 
 
 condenser varies directly with the square of the potential to which 
 it is charged, it is evident that there exists a definite relation between 
 the dielectric strength of the medium (glass) and the volume per 
 unit of energy which it is desired to store. This is equivalent to 
 saying that a great amount of energy could be stored in a very small 
 condenser if the dielectric could stand an exceedingly high potential. 
 Hence, the object to be attained in the designing of condensers for 
 radiotelegraphy is a maximum energy-storing ability with a minimum 
 of cost, size, and weight of glass. In practice it is better to use a good 
 grade of glass free from lead and other impurities. Oil condensers 
 are sometimes used, constructed of sheets of brass or zinc, and im- 
 mersed in "transformer oil." Adjustable condensers, made as shown 
 in Fig. 30, are often used for purposes of tuning; their capacity may 
 be varied by withdrawing the plates, thereby reducing the effective 
 area. Braun employed small condensers made of test-tubes covered 
 with tin-foil inside and out for short-distance low-power stations. 
 
 48 
 
RADIOTELEGRAPHIC APPARATUS 49 
 
 Quart or gallon Leyden jars are often employed, lending themselves 
 very well to the requirements. 
 
 Tuning Coils. In order to facilitate the tuning, or syntonizing, of 
 the oscillatory circuits included in a system of radiotelegraphy, some 
 apparatus for varying the electrical dimensions of such a circuit is 
 usually employed. These tuning devices consist simply of a variable in- 
 ductance, or of an adjustable condenser to vary the capacity, or of both 
 embodied in a single piece of apparatus. As the inductance factor 
 lends itself more readily to a simple method of variation, numerous 
 forms of adjustable inductance coils have been devised, the design 
 of which depends upon the circuit they are to be employed with. 
 
 Tuning coils for use with the transmitting side of a station are 
 characterized by a comparatively few turns of very heavy wire or 
 metal ribbon wound spirally on an insulated drum or ebonite cylinder. 
 Connection is made at any point on the spiral conductor either by 
 means of flexible connecting cords provided with metallic clips, or 
 by the use of a sliding connection so arranged as to permit of any 
 desired length of the inductive conductor being included in the circuit. 
 Many systems utilize the space within the turns of inductive resist- 
 ance for the placing of the condensers, thus greatly economizing the 
 room otherwise required for these two portions of the apparatus. 
 
 As the receiving circuits usually possess much less capacity 
 than the transmitting circuits, the tuning coils designed for connec- 
 tion therewith have a much larger number of turns. Such coils 
 are generally constructed with several hundred turns of rather fine 
 wire wound on a large bobbin having two sliding contacts so arranged 
 as to include between them any desired number of turns. These 
 coils are made in a great variety of ways. 
 
 Spark Gaps. An important element of the transmitting station 
 is the gap, across which the stream of sparks takes place. In a previous 
 chapter attention has been called to the resonator of Hertz and to 
 the metallic balls between which he produced his oscillatory spark. 
 In his book on "Electric Waves" published in English in 1894, he 
 advises that these balls be highly polished. For the small amount 
 of energy used by Hertz this was no doubt advantageous, particularly 
 in the production of short waves; but with the further development 
 of the art it became evident that it was impossible to maintair 
 such surfaces when employing sparks of great volume. The essen- 
 
50 
 
 WIRELESS TELEGRAPHY 
 
 tial condition to be fulfilled is that the discharging surfaces 
 shall maintain a permanent condition and not be burned away and 
 pitted by the rapidly recurring heat of the spark. With the utiliza- 
 tion of radiators of high power, and with the employment of trans- 
 formers capable of charging large capacities, the need of a means 
 for maintaining a constant condition of the spark gap became im- 
 perative. Special appliances were devised to prevent the pitting of 
 the balls and their consequent destruction. 
 
 Marconi early adopted the Righi oscillator plan of placing the 
 balls in a chamber of oil, or other highly insulative medium, thereby 
 excluding the oxygen of the air from the balls and preventing oxidiza- 
 tion. He soon found, however, that the insulating fluid was rapidly 
 decomposed under the influence of the more powerful discharges 
 and abandoned the idea in favor of a "dry" ball system. 
 
 Numerous inventors have contrived many so-called multiple- 
 ball exciters, among whom is J. S. Stone, whose oscillator is shown 
 in Fig. 31. R. A. Fessenden has conducted numerous experiments 
 
 which seem to indicate that there is great 
 advantage to be gained by causing the 
 spark to take place in a compressed-air 
 chamber. This is explained by the fact 
 that the effective potential between the 
 balls is thereby raised without rendering 
 the spark non-oscillatory. Better radia- 
 tion is possible also, according to Fes- 
 senden, and it is undoubtedly a great 
 improvement in reducing the ear-splitting 
 noise of the customary discharge. Various compressed gases have 
 also been used with varying success. 
 
 Among the various forms of exciter which have more or less 
 successfully fulfilled the requirements, mention must be given to one 
 other fundamental form employed by Marconi. It took advantage 
 of the important fact that though it is exceedingly difficult to create 
 a true alternating arc between two relatively moving surfaces, never- 
 theless an electric oscillation from a condenser can readily take place 
 even though the movement be exceedingly rapid. Marconi, there- 
 fore, devised what is known as the high-speed disk discharger, shown 
 in Fig. 32. It would seem that this design of gap possesses many 
 
 Fig. 31. Multiple-Ball Exciter 
 
 50 
 
RADIOTELEGRAPHIC APPARATUS 
 
 51 
 
 advantages as attested by the extensive employment of it at the trans- 
 Atlantic stations. The illustrations make clear the connections. 
 The apparatus consists of two metallic disks A and B, revolving 
 at high speed, and a second larger disk at right angles to the axis of 
 the other two and between them, also revolving at high speed. There 
 are thus two gaps where sparks may take place. The closing of the 
 key charges the condensers C and D, in series between which is con- 
 nected the condenser E, which discharges the energy across either 
 
 AER/AL 
 
 EARTH 
 
 Fig. 32. Diagram of Marconi High-Speed Disk Discharger 
 
 gap between the rapidly revolving terminals. Another modification 
 of this device, shown in Fig. 33, is characterized by the fact that it is 
 designed for use with a direct current. The mechanical construc- 
 tion is similar to that of the form previously described, with the ex- 
 ception that the large disk has a row of metallic studs placed equi- 
 distantly around its circumference in such a manner as to greatly 
 shorten the length of the air gap between the two revolving terminals 
 
 51 
 
52 
 
 WIRELESS TELEGRAPHY 
 
 when the said studs occupy a position in a line with the plane of their 
 rotation. The office of these studs is to shorten the air gap at pre- 
 determined and equal intervals, thus discharging the condensers, 
 which are immediately charged by the direct current. In both forms 
 of the device the arc is prevented by the rapid rotation of the revolv- 
 ing parts. It is claimed that the Marconi dischargers permit of great 
 rapidity of signaling. The last described produces, when run at very 
 high speed, an almost continuous train of oscillations. 
 
 AER/AL 
 
 D/ffECT 
 CURRENT 
 
 XEVOLV/NG DISK 
 
 $TL/DS EARTH 
 
 Fig. 33. Disk Discharger for Use with Direct Current 
 
 High-Frequency Alternators. It was known at an early date 
 in the history of radiotelegraphy that a much greater efficiency could 
 be achieved if a means were devised for creating a continuous train 
 of undamped oscillations. The Morse dot, which is the minimum 
 signal, was seen to be composed of a considerable number of separate 
 trains of waves, each rapidly damped. Could these "gaps" in 
 the wave train be filled up, the received signal would not only be 
 
 52 
 
RADIOTELEGRAPHIC APPARATUS 53 
 
 stronger, but selective signaling would also be greatly facilitated 
 and precise tuning be more easily accomplished. A moment's 
 thought will suffice to convince that a continuous train of undamped 
 oscillations would be the exact equivalent of a continuous alternating 
 current of extremely high frequency; and this opens up the possibility 
 of employing generators which might be connected directly with the 
 aerial, thus doing away with the intermediate condenser and spark 
 gap. 
 
 Many attempts have been made to construct generators df suf- 
 ficiently high frequency, the majority of them having been of the in- 
 ductor type. An exceedingly small electrical output seems to be the 
 characteristic of all attempts thus far to produce such a machine. 
 Great speed of rotation of the disk armature is required in this type 
 of generator, and as there are limits beyond which it is unsafe to push 
 the rotation, fundamental difficulties arise which have not as yet been 
 surmounted with any degree of commercial success. Fessenden 
 claims to have produced an alternator giving a frequency of 80,000 
 cycles. The wattage is said to be about 250. The ingenious Ger- 
 man inventor, Ernst Ruhmer, has also constructed an alternator 
 of the inductor type having a frequency of 300,000 and an output 
 of but .001 watt; and W. Duddell has succeeded in producing a 
 frequency of 120,000 with somewhat greater power. Until it is 
 possible to greatly increase the output of such machines, their use 
 will be limited to laboratory experiments, or at most to short- 
 distance work in connectior with rs iiotelegraphy. Their develop- 
 ment at the present time seems to be in connection with radio- 
 telephony. 
 
 The Singing Arc. Much more successful have been the attempts 
 to produce a continuous train of undamped oscillations from a direct 
 current, Elihu Thomson applied, in 1892, for a United States patent 
 en a method intended to effect such a transformation, Fig. 34. A 
 source of direct current is connected to a circuit having a very high 
 inductance, and a spark gap across which is shunted a condenser, 
 and smaller inductance in series. The inventor claims in his patent 
 specifications that the gap, inductance, and capacity can be so ad- 
 justed that the condenser is periodically discharged across the gap 
 at frequencies as high as 40,000 per second. 
 
 The form that this apparatus has since taken is known by the 
 
 53 
 
54 
 
 WIRELESS TELEGRAPHY 
 
 name of Duddell singing arc, on account of the further developments 
 introduced by him in 1900. Duddell substituted a carbon arc for 
 the gap, and found that such an arrangement produced a clear 
 
 OSCILLATORY 
 C/RCU/T 
 
 Fig. 34. Thomson Direct-Current Method of Generating 
 Oscillations 
 
 musical note plainly audible some distance away, the pitch of the 
 note depending on the value of the capacity and the inductance in the 
 oscillatory circuit the latter is represented by the heavier lines in 
 Fig. 35. The best effects were obtained by the use of solid rods of 
 
 OSCILLATORY 
 CIRCUIT 
 
 Fig. 35. Duddell Singing Arc 
 
 carbon. The resistance of the inductance in the oscillatory circuit 
 must be low about 1 ohm. Duddell found it difficult to produce 
 oscillations of any considerable power above a frequency of about 
 10,000; although other experimenters have succeeded in reaching 
 a frequency of 400,000 with small capacity and little energy. 
 
 It remained for Valdemar Poulsen of Copenhagen to make the 
 greatest improvement in the direct-current arc method of producing 
 
 54 
 
RADIOTELEGRAPHIC APPARATUS 
 
 55 
 
 oscillations. Fig. 36 shows Poulsen's arrangement. In the first 
 place, he enclosed the arc in an air-tight chamber filled with coal 
 gas, and used a water-cooled positive electrode with a carbon negative. 
 He also introduced into the chamber the polar projections of two 
 powerful electromagnets in such geometrical relation as to cause the 
 lines of force to pass directly between the electrodes as shown in the 
 diagram. The connecting lines make clear the circuit. The funda- 
 mental similarity to Thom- 
 son's circuit is apparent. It 
 is possible to produce very 
 powerful undamped oscilla- 
 tions with this apparatus, the 
 frequency of which may, by 
 the proper adjustment of the 
 capacity and the inductance, 
 be made as high as 1,000,000 
 or more. There is a partic- 
 ular length of arc, called the 
 "active" arc, which gives the 
 best results. Poulsen's de- 
 vice is operable with many 
 other gases besides the one 
 mentioned. The magnets S 
 and N must be very power- 
 ful. 500 volts seems to be a practical voltage for use with this device. 
 Aerials. The aerials at present used are of many kinds, ranging 
 from the short length of weatherproof wire extending from an upper 
 window to a nail in the chimney, proclaiming the abode of a juvenile 
 experimenter, to those enormous structures taxing the resources 
 of modern engineering in their construction, which achieve trans- 
 Atlantic communication. It was early recognized that the radius 
 of communication was greatly extended by increasing the capacity of 
 the aerial; which fact has led to the employment of multiple-wire 
 antennae. Figs. 37, 38, 39, and 40, show some of the commoner 
 forms, conditions usually determining the choice. It was found by 
 experiment that the capacity of two wires suspended in the air was 
 not twice the capacity of one, nor four wires twice the capacity of 
 two, if such wires were placed near together. The reason, therefore, 
 
 Fig. 36. Poulsen Direct-Current Method of 
 Generating Oscillations 
 
 55 
 
56 
 
 WIRELESS TELEGRAPHY 
 
 is apparent why in many of the aerials the individual wires are 
 separated to comparatively great distances. 
 
 It is of extreme importance that the upper end of suspended 
 radiator wires should be exceptionally well insulated, and the reason 
 is obvious. Specially designed porcelain or glass insulators are 
 used, having two holes through which the ends of the wires are bound. 
 
 Aluminum wire serves excellently for the purpose of antennae 
 when the strain upon it is not too great. Its low tensile strength 
 
 ^^ 
 
 i 
 
 Fig. 37. 
 
 Fig. 38. Fig. 39. 
 
 Standard Forms of Aerial 
 
 Fig. 40. 
 
 precludes its use in some cases. A simple manner of suspending 
 a single-wire experimental aerial is shown in Fig. 41. The mast, or 
 short flag-pole, may be lashed to the tallest object available and 
 the wire carried out of perpendicular a sufficient distance to pre- 
 vent it from hitting the pole. In army field-equipment, kites or 
 captive balloons are often used to elevate the aerial wire, which 
 is carried wound upon a reel. Many aerials are arranged with a 
 tail block on a cross-tree in order that they may be let down from a 
 high mast for inspection purposes. Such aerials are of the cage 
 variety shown in Fig. 38. An idea of the construction of antennae 
 when designed for use in connection with high-power stations may 
 be gained from Fig. 42. 
 
 56 
 
RADIOTELEGRAPHIC APPARATUS 
 
 57 
 
 Directive Antennae. Many efforts have been made to direct 
 the transmission of radiotelegraphic signals to any desired point or 
 locality, but with indifferent success. 
 Early attempts embodied the use of large 
 reflectors behind the oscillator; but the 
 most encouraging results have been ac- 
 complished by the use of what are known 
 as horizontal antennae, the subject of a 
 patent granted to Marconi and dated 
 1904. DeForest has also met with some 
 success along this line. The results ob- 
 tained by these investigators are not 
 formulated well enough as yet to war- 
 rant a description of them here. 
 
 Detectors. The subject of the re- 
 ception of wave-trains and the transfor- 
 mation of their energy into visual or 
 audible signs through the agency of suit- 
 able translating devices will now be taken 
 up and described. It is helpful toward a 
 comprehension of this part of the subject 
 to get clearly in mind the primary effect 
 of a train of waves upon a receiving aerial, namely, the creation of an 
 
 Fig. 41. Single Wire Experi- 
 mental Aerial 
 
 Fig. 42. Antennae Construction for High-Power Station 
 
 alternating electromotive force. And the prime function of a receiv- 
 ing device is broadly to detect the presence of a high-frequency 
 
 57 
 
58 
 
 WIRELESS TELEGRAPHY 
 
 alternating current of minute value. Volumes could be written on 
 the history of the various forms of receiving devices which have 
 occupied the attention of the various investigators in this interesting 
 field of experiment. In the present instance attention will be called 
 to those forms only which have proved themselves of practical value. 
 
 Wave-detecting devices may be classified for convenience 
 according to the physical principle on which they act, such as thermo- 
 electric, magnetic, electrolytic, chemical, photo-electric, physiological, 
 etc. This course will be followed as far as practicable. 
 
 Coherers. Coherers work on the principle of imperfect contact 
 and are called self-restoring and non-restoring according as their sensi- 
 
 FLAN 
 
 Fig. 43. Lodge-Muirhead Detector 
 
 tiveness is automatically reassumed after the passage of a train of 
 waves, or must be superinduced by some external agency. Com- 
 mercially the coherer has become almost obsolete. 
 
 Branly Coherer: It is unnecessary at this point to give more 
 than passing mention to the Branly coherer, as it has been fully 
 described in a previous chapter. As improved by Lodge and Mar- 
 coni it performed a very important function in the early days of radio- 
 telegraphy, but has now fallen into disuse. 
 
 Lodge-Muirhead Coherer: An interesting form of contact 
 detector is shown in Fig. 43, devised by Lodge and Muirhead. It 
 consists of a slowly moving steel disk a whose sharpened edge is 
 prevented from coming into contact with the small globule of mer- 
 cury 6 by means of a thin film of oil interposed between the 
 mercury and the steel and contained in the recess d. Oscillations 
 passing through the oil cause a breakdown of its high resistance, 
 
 58 
 
RADIOTELEGRAPHIC APPARATUS 59 
 
 permitting a translating device to operate by reason of the improved 
 conductivity. Upon cessation of the oscillations, the movement of 
 the disk re-establishes the initial receptivity. 
 
 Italian Navy Coherer: The Marconi Company used with suc- 
 cess for a time the so-called "auto-coherer" invented by Signor 
 Castelli, and often referred to as the Italian Navy coherer. The 
 
 c' 
 
 Fig. 44. Castello "Auto-Coherer" 
 
 action is entirely automatic. In Fig. 44, z is an iron cylinder separa- 
 ting two globules of mercury; c and c' are of carbon. Cohesion 
 between the mercury globules and electrodes exists only under the 
 stimulus of the oscillations. 
 
 Tantalum-Mercury Coherer: The tantalum-mercury imperfect- 
 contact detector invented by L. H. Walter is the simplest as well as 
 one of the best of the self-restoring coherers. A small portion of the 
 filament of a tantalum incandescent lamp is connected to a piece of 
 platinum wire for terminal purposes, and the tip of the tantalum is 
 immersed in mercury, which thus forms the other terminal. The 
 whole may be sealed up in a vacuum to avoid oxidization of the 
 mercury. The contact offers very high resistance to a small e. m. f., 
 but falls very low under the influence of the received oscillations. 
 It is rapidly self-restoring. Telephone receivers are often used with 
 this class of detector instead of the Morse relay and recorder, thus 
 allowing the detection of signals from much greater distances owing 
 to the extreme sensitiveness of the Bell instrument to minute differ- 
 ences of current. Such a receiver responds by a buzz to the Morse 
 dash from the distant station. 
 
 Valve, or Rectifier, Detectors. One of the difficulties of de- 
 tecting electric oscillations is the fact that they are of an alternating 
 nature. With the present means at our disposal it cannot be said 
 that we can detect the presence of minute alternating currents with 
 the ease with which we can detect direct currents of equal value. 
 This has led to endeavors to rectify the high-frequency alternations 
 of the received oscillations. Detectors of this type are known as 
 valve, or rectifier, detectors, and one of the simplest means of detect- 
 ing radiotelegraphic signals is afforded by such devices. To their 
 
 59 
 
60 
 
 WIRELESS TELEGRAPHY 
 
 extreme simplicity is due to a large extent the present number of 
 amateur wireless installations to be seen on all sides. The action 
 of the silicon detector, shown in Fig. 45, is due to the fact that a con- 
 siderable number of substances in nature possess the property of 
 unilateral conductivity, or the property of conducting electricity 
 freely in only one direction. H. H. C. Dunwoody discovered that 
 carborundum possessed this property to a very marked degree, and 
 would act as a detector if introduced into a receiving circuit in place 
 of a filings coherer. He later observed that no battery was necessary 
 
 when using a telephone receiver 
 shunted by a small condenser, 
 as shown in Fig. 46. The fol- 
 lowing substances will all act in 
 place of the carborundum: cop- 
 per pyrites, iron pyrites, galena, 
 silicon, zinc oxide (perikon), mol- 
 ybdenum sulphide, and titanium 
 oxide. G. W. Pierce has found 
 that the resistance of these sub- 
 stances may be 3,000 times 
 greater in one direction than in 
 the other. The theory of this 
 peculiar action cannot as yet be 
 said to be complete. 
 
 Carborundum, silicon, and 
 perikon seem to be the most satis- 
 factory, particularly silicon, which 
 
 makes a very sensitive and inexpensive device. Such materials used 
 as detectors of electric waves allow but one-half of each wave to pass, 
 thus giving rise in the telephone to a rapidly pulsating current in 
 one direction to which the telephone can respond. The energy of the 
 oscillations, therefore, directly achieves the audible signal. It has 
 been found, however, that in some cases better results are obtained 
 with a shunted battery cell in the circuit. It is important when using 
 any form of valve detector that excellent connection with the crystal 
 should be maintained at least on one terminal, a deposit of some suit- 
 able metal often being employed, thus permitting of a large area of 
 contact. The adjustable contact is preferably pointed and securely held. 
 
 Fig. 45. Silicon Detector 
 
 60 
 
RADIOTELEGRAPHIC APPARATUS 
 
 61 
 
 AZfflAL 
 
 Glow-Larnp Detector: The glow-lamp detector, invented by 
 Prof. J. A. Fleming, was one of the first valve detectors. The theory 
 of its operation may be understood from the inventor's description 
 and with reference to Fig. 47. "An ordi- 
 nary incandescent lamp with carbon fila- 
 ment has a metal plate included in the 
 glass bulb, or a metal cylinder C placed 
 round the filament, the said plate or 
 cylinder being attached to an indepen- 
 dent insulated platinum wire T sealed 
 through the glass. When the carbon 
 is rendered incandescent by electric 
 current, the space between the filament 
 and the plate, occupied by a highly 
 rarefied gas, possesses a unilateral con- 
 ductivity, and negative electricity will 
 pass from the incandescent filament to 
 the plate, but not in the opposite 
 direction. This effect depends upon the 
 well-known fact that carbon in a state 
 of high incandescence liberates electrons 
 
 or negative ions; that is to say, point charges of negative electricity. 
 These electrons, or corpuscles, are constituents of the chemical 
 atom. Hence a carbon filament in an incandes- 
 cent lamp is discharging from its surface nega- 
 tive electricity, which may even amount to as 
 much as an ampere or even several amperes per 
 square centimeter. If, then, an incandescent 
 lamp made as described has its filament rendered 
 incandescent by a continuous current, and if 
 another .circuit is formed outside the lamp con- 
 necting the negative terminal of the filament 
 with the insulated metal plate or cylinder in the 
 bulb, and if oscillations are set up in this circuit, 
 negative electricity will be able to move through 
 this circuit from the filament to the plate inside the bulb, but not 
 in the opposite direction." 
 
 It is evident from the foregoing that there are present in the 
 
 FAffTH 
 
 Fig. 46. Diagram of Dun 
 woody Detector 
 
 Fig. 47. Fleming 
 Glow-Lamp Detector 
 
 61 
 
62 
 
 WIRELESS TELEGRAPHY 
 
 glow-lamp device the essentials of a valve detector. Fig. 48 shows 
 a receiver circuit employed by Marconi making use of the Fleming 
 
 lamp. Instead of passing the 
 rectified uni-directional impulses 
 directly through the telephone, 
 they are passed around the 
 secondary of a large induction 
 coil in series with a condenser, to 
 the primary of which the tele- 
 phone receiver is connected. 
 Prof. Fleming is authority for 
 the statement that this arrange- 
 ment, when suitably adjusted, is 
 "one of the best long-distance 
 receivers for electric waves yet 
 devised." 
 
 Audion: The so-called au- 
 Fig. 48. Marconi circuit Using dion of DeForest is a modifica- 
 
 Fleming Detector . 
 
 tion oi the r leming detector just 
 
 described. Fig. 49 shows its connection [n a receiving circuit. The 
 lamp used has a low- voltage tantalum filament with two wings, or 
 terminals, sealed in the bulb, as shown. This detector is said to 
 be fairly sensitive, though of short life. 
 
 Magnetic Detectors. During the summer of 1902, Marconi was 
 successful in receiving signals sent out from Poldhu on the coast of 
 
 Cornwall to Flace Bay, Nova 
 Scotia, by means of a re- 
 markably ingenious magnetic 
 receiving device invented by 
 himself and called a magnetic 
 detector. Since that time 
 many devices have been pat- 
 ented depending for their op- 
 eration upon the magnetic 
 
 Fig. 49. Receiving Circuit with Audion Detector effeCtS f the electric OScilla- 
 
 tions. There has been much 
 
 discussion relative to the action involved in the Marconi device as 
 well as in other modifications based on the magnetic phenomena 
 
 62 
 
RADIOTELEGRAPHIC APPARATUS 
 
 63 
 
 associated with oscillatory currents. The explanation advanced by 
 Marconi himself will, therefore, be given here, which in substance 
 is as follows, reference being made to Fig. 50. 
 
 The aerial and ground are connected to a few turns of rather 
 heavy wire wound upon a glass tube T over which, but insulated 
 from it, is another coil inductively related to the first and connected 
 to the terminals of a telephone receiver. Two strong permanent 
 magnets are placed with like poles together, as indicated. P and P' 
 are two pulleys carrying on their periphery an endless belt composed 
 of several fine wires of about No. 36 gauge, which are made to pass 
 
 Fig. 50. Diagram of Marconi Magnetic Detector 
 
 continually through the axis of the coils by a train of gears not shown. 
 Owing to the hysteresis of the material of the band it tends to retain 
 its magnetism for a short period after it has passed out of the strongest 
 part of the field; but if a train of waves from the aerial is passed 
 through the primary coil to the ground, the effect is to annul the 
 hysteresis and thereby to hasten the demagnetization of the iron 
 wire. This action results in a variation of the flux in the secondary 
 winding, thus inducing electromotive forces in the secondary coil, 
 which make themselves audible in the telephone as a series of sharp 
 ticks. This is said to be one of the most sensitive devices ever 
 made. 
 
 A diagrammatic drawing of a magnetic detector, invented by 
 H. Shoemaker, which very closely resembles the early embodiment of 
 
 63 
 
64 
 
 WIRELESS TELEGRAPHY 
 
 the Marconi apparatus is shown in Fig. 51. There have been many 
 variations of the magnetic detector but space will not permit of a 
 description of less important forms. 
 
 Thermo-electric Detectors. Comprehended under the head oi 
 thermo-electric detectors are those instruments which depend for 
 their action on the heating effects of the oscillatory currents. These 
 
 Fig. 51. Shoemaker Magnetic Detector 
 
 detectors are especially useful in making quantitative measurements 
 of the amount of energy received under a given condition, and indeed 
 find their greatest utility therein. Fessenden has given great care to 
 his investigations of this form of detector with the result that his 
 so-called "barreter" shown in Fig. 52 is of the same order of sensitive- 
 ness as the coherer. It consists of a short piece 
 of exquisitely fine platinum wire connected to 
 suitable terminal wires and the whole enclosed 
 in a vacuum bulb. The temperature rises rap- 
 idly under the action of the oscillations, causing 
 an increase in resistance which is indicated by a 
 Wheatstone bridge, in the circuit of which the 
 detector is connected as one of the arms. At- 
 tempts have been made to apply the phenomena 
 of the thermo couple in this connection, but with 
 only qualified success. It would seem for many reasons that thermo- 
 electrical detectors will not be able to compete with other forms in 
 long-distance work. 
 
 Fier. 52. Fessenden 
 Barreter 
 
 64 
 
RADIOTELEGRAPHIC APPARATUS 
 
 65 
 
 Fig. 53. Liquid Barreter 
 
 Electrolytic Detectors. It remains to take up the class of de- 
 tectors known as electrolytic. DeForest's name is associated with 
 this variety of receiving device, as it was first extensively used by 
 him in a form invented by himself. It consists of a glass tube \ inch 
 in diameter enclosing conductor plugs 
 after the manner of the Branly coherer. 
 In the interspace is placed a paste com- 
 posed of rather coarse filings worked up 
 with an equal quantity of oxide of lead 
 in glycerine or vaseline with a trace of 
 water or alcohol. Its resistance in- 
 creases during the passage of the wave 
 train. 
 
 Fessenden Liquid Barreter: The 
 most sensitive and practical electrolytic 
 detector is the liquid barreter invented 
 by Fessenden, Fig. 53. It consists essen- 
 tially of a small containing vessel filled with nitric acid into which 
 projects a platinum wire electrode, which is of extremely small diam- 
 eter. The apparent resistance of the cell is greatly reduced by the 
 oscillations. The exact nature of the action is not agreed upon by 
 investigators. It was with a refined form of this detector that trans- 
 Atlantic signals were first received from Scotland by the National 
 Electric Company at Brant Rock, Massachusetts. 
 
 Hozier-Brown Detector: The Hozier-Brown system of wire- 
 less telegraphy employs a detector classified by some as depending 
 on imperfect contact, but by others as 
 being electrolytic in its action. It con- 
 sists of a small portion of peroxide of 
 lead held between terminals of lead and 
 platinum, Fig. 54. The lead terminal 
 is much smaller than the other, being a 
 blunt point rendered adjustable by a 
 
 knurled screw. A two-volt accumulator Fig - 54 - Hosier-Brown Detector 
 
 connected in series gives the best results, according to the inventor. 
 
 Electrodynamic Detectors. Mention might be given in passing 
 
 to the electrodynamic detector devised by Fessenden, although it 
 
 has never been used extensively. It is designed to operate on the 
 
 65 
 
66 WIRELESS TELEGRAPHY 
 
 principle that a metallic disk, suspended in a circular coil through 
 which an alternating current is flowing, and at an angle of 45 degrees 
 to the plane of winding of the coil, tends to turn so as to take up a 
 position at right angles to the plane of the coil. This was a fact 
 discovered independently by Elihu Thomson and J. A. Fleming. 
 Fessenden used an extremely light disk hung by a quartz fiber, and 
 he succeeded in obtaining marked deflections of a beam of light 
 reflected from a small mirror fastened to the disk. This device, 
 like the thermo-detector, has been of great service in making quan- 
 titative measurements of oscillatory currents. 
 
 Auxiliary Apparatus. It would be beyond the scope of the 
 present work to give ?n extended discussion of the various small 
 devices used in connection with the local receiving circuits, as many 
 of the instruments are not in any way peculiar to radiotelegraphy, 
 being the common adjuncts of wire telegraphy. Mention will only 
 be given to a few points of importance wherein such appliances differ 
 from those commonly employed. 
 
 The relay supplied by makers of telegraphic instruments is 
 usually wound with an insufficient number of turns to be efficiently 
 used in connection with a coherer and local battery as a means of 
 actuating a Morse recorder. Rewinding is, therefore, often resorted 
 to. Polarized relays are found to be the best suited to this class of 
 work and should be wound to a very high resistance in connection with 
 all potentially operable detectors. No. 40 wire is often employed. 
 
 Sparking at the contacts of the relay is often prevented by the 
 employment of four or five so-called "polarized" cells shunted across 
 the contacts. They are made by inserting a pair of platinum wires 
 through the cover of a small containing vessel partly filled with dilute 
 sulphuric acid, allowing the solution to cover the ends of the electrodes 
 thus formed. 
 
 The telephone receivers for use with many forms of detector 
 are much more efficient if wound to a higher resistance than is neces- 
 sary in the common commercial instrument. Receivers are manu- 
 factured in a great variety of forms, only differing from one another 
 in some slight structural modification. The kind known as operator's 
 double-head receivers of the watch-case design wound to a resistance 
 of about 500 or 1,000 ohms are well adapted to the requirements of 
 radiotelegraphy. 
 
 66 
 
RADIOTELEGRAPHIC APPARATUS 67 
 
 Dry cells developing an electromotive force, when fresh, of about 
 1.5 volts are generally used in the local recorder and tapper circuits. 
 One such cell is frequently used in the relay and the coherer circuit. 
 
 Measuring Instruments. Perhaps in no department of electro- 
 technics are the quantitative values of the electrical measurements 
 of more vital importance than in the science of radiotelegraphy. 
 A well-equipped station, therefore, possesses efficient instruments 
 for the measurement of the various electrical factors involved. Be- 
 sides the common appliances of this nature, such as the voltmeter, 
 ammeter, Wheats tone bridge, etc., it is highly advisable to have the 
 requisite means for making accurate determinations of capacity and 
 inductance. Wave-lengths can be measured by wave-meters, or 
 cymometers. These devices are now on the market and are of great 
 utility in a wireless station. 
 
 67 
 
CHAPTER V 
 SYSTEMS OF RADIOTELEGRAPHY 
 
 The history of radiotelegraphy repeats once more the old story 
 that is so often connected with great inventions. The world being 
 possessed of a new scientific principle, many minds in many parts 
 of the world are simultaneously bent upon its practical application, 
 with the result that the fundamental principle finds embodiment in 
 various methods of accomplishing a similar purpose. The startling 
 nature of the discovery of electric waves was bound to give rise to 
 unprecedented activity in the field of experimental investigation; 
 and such experiments as were particularly successful were bound to 
 prompt investigators to seek patent protection on their modifications; 
 and this in turn gave rise to numberless "systems" of radiotelegraphy. 
 
 A voluminous list of names could be given of those who have 
 contributed to the advancement of radiotelegraphy in regard to both 
 theory and practice. Among the best-known American investigators 
 are Fessenden, DeForest, Clark, Stone, and Massie. Each of these 
 men has devised a system which bears his name. In England the 
 work has been carried on by men of such unqualified distinction as 
 Lodge, Alexander Muirhead, Fleming, Thomson, and Rutherford. 
 Slaby, Arco, and Braun are the names best known in Germany. The 
 French are represented by Ducretet, Branly, Rochefort, and Tissot, 
 besides other men of lesser fame. We have seen how largely Italy 
 has contributed to the subject; besides Marconi and Righi, mention 
 should be made of Solari, Castelli, and Tommasina. Baviera in 
 Spain, Popoif in Russia, Schafer in Austria, Guarini in Belgium, and 
 Ricaldoni in the Argentine Republic have all invented systems which 
 have been more or less used in their respective countries. The 
 Japanese have also devised a system that successfully stood the test 
 of service in the Russo-Japanese war. 
 
 The development of the art in the various countries has been 
 carried on largely by representative investigators, and in many in- 
 
 68 
 
SYSTEMS OF RADIOTELEGRAPHY 69 
 
 stances the governments have adopted a system exploited by their 
 subjects. The United States government, however, has purchased 
 and experimented with most of the prominent systems offered, and 
 as a result the army and navy equipments comprehend quite a variety 
 of apparatus of different makes. 
 
 Telegraphic Codes. Before beginning the description of the 
 more important systems of radiotelegraphy in use at the present time, 
 we will consider the telegraphic codes employed in wireless corre- 
 spondence. There are three alphabetical codes commonly used at 
 the present time, viz, the Continental, the Morse, and the Navy 
 
 *4i 
 
 B 
 
 mm 
 
 m.mm ^i 
 
 
 
 
 G 
 
 H 
 
 
 
 / ^ 
 
 K 
 
 L 
 
 mm 
 
 M 
 
 N 
 
 ^? /= 
 
 
 /? 
 
 V V 
 mm mm 
 
 . mmmm. mm 
 
 w 
 
 i mm 
 
 Z' WAJT UNDERSTAND DONT UNDERSTAND 
 
 PERIOD 
 
 
 /NTERROGAT/ON 
 mm mm 
 
 EXCLAMATION 
 
 
 
 
 3 
 
 4 5 
 mm 
 
 6 
 mm 
 
 mmmm... mmmm^mm.. 
 
 mmwmmm 
 
 ~ 
 
 CALL 
 
 mL^mm. 
 
 
 Fig. 55. Continental Code 
 
 codes. By far the greatest amount of business is carried on in the 
 Continental code, especially between ships and shore stations. The 
 Morse is more commonly employed for overland service, while the 
 Navy code is confined to naval purposes. Abbreviations of the com- 
 moner words are often made use of in transacting the ordinary run 
 of business. The three codes are shown in Figs. 55, 56, and 57. 
 Marconi System. A detailed description has already been given 
 of the Marconi system as it was about the year 1900. Since then the 
 system has been developed to a remarkable degree so that it stands 
 today a commercial factor of large pretensions. The Marconi 
 
 69 
 
70 
 
 WIRELESS TELEGRAPHY 
 
 stations are scattered in many parts of the globe and are operated 
 in conjunction with all the large telegraph and cable companies. 
 
 A 
 
 & 
 
 
 
 C 
 
 
 
 _ 
 
 E 
 
 
 
 
 
 
 H 
 
 
 
 
 J 
 
 n.._ 
 
 
 // 
 
 . 
 
 : 
 
 . 
 
 P 
 
 
 .... 
 
 ft 
 
 
 
 S 
 
 
 T 
 
 u 
 
 mm 
 
 I/ 
 mm 
 
 J 
 
 X 
 
 
 Y 
 
 
 
 
 & 
 
 
 < 
 
 .-_. 
 
 
 
 ../-. 
 
 <? 
 
 
 PttfOD 
 
 
 /NTEffftOGA T/ON 
 
 
 
 S 
 
 6 
 
 
 
 
 .? 
 
 COMMA 
 
 EXCLAMAT/ON 
 
 9 
 
 () 
 
 
 
 COLOA/ 
 
 ! 
 
 SEM/ COLON 
 
 
 Fig. 56. Morse Code 
 
 In addition to the numerous land stations a very large number of 
 vessels are equipped with the Marconi apparatus, including the 
 
 ^U 
 
 -<- 
 
 .-. 
 
 .-- 
 
 ^ 
 
 
 
 .. 
 
 /y^ 
 
 / 
 
 
 
 j 
 
 mmmm . 
 
 X 
 
 .4.* 
 
 L< 
 
 /v 
 
 
 
 ^ 
 
 . 
 
 d? 
 
 
 
 ft 
 
 i 
 
 -.- 
 
 ^ 
 
 U 
 
 mm 
 
 ^K 
 
 in/ 
 
 
 ..-. 
 
 r 
 
 
 
 ^^ 
 
 
 
 W 
 
 ? <9/p 
 
 UNDER 
 
 STAND 
 
 / 
 
 
 
 2 
 
 3 
 
 mm 
 
 4 
 
 
 6 
 
 7 
 
 <9 
 
 Q 
 
 o 
 
 
 
 
 
 
 * mmmm * 
 
 
 Fig. 57. Navy Code 
 
 ocean liners of nearly all the large steamship companies, such as the 
 Cunard line, the Hamburg-American line, the Norddeutscher Lloyd, 
 
 70 
 
SYSTEMS OF RADIOTELEGRAPHY 
 
 71 
 
 and many other lines too numerous to mention. Three stations are 
 in operation in China. 
 
 For short-distance equipment to be used over a few hundred 
 miles, such, for instance, as is usually installed on Atlantic liners, 
 the Marconi Company employs an induction coil with mechanical 
 break to charge a battery of six to twelve Leyden jars. Two coils 
 and two sets of jars are often supplied in order to readily produce 
 two different wave-lengths. A single spark gap is now used. The 
 Marconi magnetic detector is generally employed, owing to its great 
 simplicity and ease of adjustment. An important improvement 
 evolved by the meeting of practical difficulties is known as the X- 
 stopper, X being the name given to certain irregular atmospheric 
 disturbances of an electromagnetic nature which manifest them- 
 
 Fig. 58. Complete Marconi Sending and Receiving Circuit 
 
 selves as stray signals of sufficient energy to cause confusion in the 
 reception of messages. The means devised by Marconi for over- 
 coming these objectionable interruptions may be seen in diagram 
 in Fig. 58, which shows one form of the complete sending and receiv- 
 ing circuits employed by the Marconi Company. The lower end 
 of the receiving aerial is connected with a plurality of adjustable 
 oscillatory circuits of varying periodicity which terminate in the 
 primary oscillation circuit of the receiving device. The operation 
 of the contrivance depends upon the ability of the first three grounded 
 circuits to perform the function of leading to the ground waves whose 
 frequency does not accord with the periodicity of the system as a 
 whole. It will be noted that the closed type of- oscillatory circuit 
 
 71 
 
72 WIRELESS TELEGRAPHY 
 
 inductively coupled to the aerial as before described is used in the 
 transmitting arrangement of apparatus. The later form of oscilla- 
 tion transformer used at the sending station is designed to provide 
 means for varying the closeness of the inductive couple. This 
 possesses many advantages. 
 
 The Marconi Company has equipped several high-power trans- 
 Atlantic stations. The modifications of the short-distance apparatus 
 made necessary for long-distance signaling pertain largely to means 
 for controlling a much larger amount of energy at the transmitting 
 station and the employment of longer wave-lengths. Communica- 
 tion was established the latter part of 1907 between Cape Breton, 
 Nova Scotia, and Clifden, Ireland, by waves 12,000 feet in length 
 generated by means of the Marconi high-speed disk discharger used 
 in conjunction with a condenser of 1.16 microfarads charged to 80,000 
 volts. Horizontal, or directive, antennae are used with their free 
 ends directed away from each other at the two stations, the hori- 
 zontal portion being about 1,000 feet long and raised about 200 feet 
 in the air. The Marconi magnetic detector, and also a modification 
 of the Fleming glow-lamp detector, have been used as receptors in 
 this class of work. fc 
 
 An ingenious form of signaling key for use in connection with 
 high-power installations employing alternating current has been 
 patented by the I Marconi Company. The fundamental feature of 
 the invention consists in the use of a laminated electromagnet 
 through which the current to be broken is conducted, so placed 
 as to hold the key closed by the attraction of an armature on the 
 key until the current reaches the zero value, at which time the key 
 is allowed to break connection unaccompanied by a spark. The 
 connection may be made and maintained at will, but upon release 
 of the key the circuit is broken at the instant when the current reaches 
 the zero value; the frequency of the alternating current being at least 
 such that this occurs about 100 times per second, the maximum lag 
 of the key behind the movement of the operator's button is inap- 
 preciable. 
 
 Fessenden System. Fessenden undoubtedly holds a position 
 of first rank among scientific investigators in the field of electric 
 radiation. Moreover, he has proven?, himself to be an inventor of 
 exceptional originality. His experiments in ladiotelegraphy date 
 
 72 
 
SYSTEMS OF RADIOTELEGRAPHY 73 
 
 back to the early days of the art. The National Electric Signaling 
 Company now control the long list of patents resulting from his 
 researches beginning in 1897 and covering a great variety of subjects 
 pertaining to every part of radiotelegraphic equipment as well as to 
 radiotelephony. 
 
 The National Electric Signaling Company completed in 1905 
 two trans-Atlantic stations for communication between Brant Rock, 
 Massachusetts, and Machrihanish, Kintyre, Scotland, a distance of 
 more than 3,000 miles. Successful communication was established on 
 Jan. 3rd, 1906, the detector used being the liquid barreter, already 
 described. An interesting feature of these long-distance stations is 
 the design of the aerial. This is in the form of a vertical steel tube 
 3 feet in diameter and 415 feet long, resting upon an insulated foun- 
 dation, and supporting an "umbrella" formed of wires at the top. 
 This structure is held in an erect position by sixteen guys insulated 
 to withstand a voltage of over 150,000. A 25-kilowatt, 60-cycle, boiler- 
 engine alternator supplies the energy. 
 
 Fessenden has devoted much time to the problems of selection, 
 interference, and tuning. As a result of his labors in this field, the 
 Fessenden system may be said to represent the highest development 
 in this respect yet achieved. 
 
 The National Electric signaling equipment comprises a transmit- 
 ting device of the direct-coupled aerial variety, characterized by the 
 arrangement of the sending key which, by cutting out a certain 
 amount of inductance in the oscillatory circuit, alters the frequency of the 
 waves emitted instead of interrupting the primary circuit and caus- 
 ing a cessation of the waves, as in common practice. This requires 
 that a receiving station be tuned with great accuracy, in order to 
 respond to a slight difference of wave-length only, an untuned cir- 
 cuit being thus unable to receive any signals other than a continu- 
 ous dash. It is claimed that a difference of wave-length occasioned 
 by the operation of the key, amounting to less than one per cent is 
 sufficient to achieve perfect communication. This exceptional free- 
 dom from interference is due largely to the employment of what is 
 called an interference preventer, diagrammatically represented in 
 Fig. 59, which shows an improved Fessenden receiving circuit. The 
 aerial is connected through a variable inductance to a divided circuit 
 and thence to the ground. In each half of the divided circuit is 
 
 73 
 
74 
 
 WIRELESS TELEGRAPHY 
 
 placed a condenser in series with the primary of an air-core oscilla- 
 tion transformer. The secondary terminals of the transformer are 
 united by a condenser A, a signal translating device consisting 
 of the liquid barreter B, a potentiometer C, and a telephone receiver 
 D all in series. The secondary terminals of the transformers are 
 connected up so as to oppose each other, after the manner of a Hughes 
 
 induction balance. The aerial 
 and one-half of the divided cir- 
 cuit are tuned to the desired 
 frequency, the other half being 
 momentarily disconnected; then 
 the latter is connected again and 
 the capacity of the condenser 
 E is adjusted until the disturb- 
 ing signals are eradicated. The 
 operation is theoretically as fol- 
 lows: Signals of the proper 
 wave-length pass almost entirely 
 through the side of the divided 
 circin't which is tuned to corre- 
 spond, while waves of any other 
 frequency pass with equal ease 
 through both sides of the di- 
 vided circuit, thereby acting dif- 
 ferentially on the secondary os- 
 cillation circuit because the sec- 
 ondary windings of the oscilla- 
 tion transformers oppose each 
 other. It is said that this arrangement will differentiate between 
 waves differing but one per cent in wave-length. 
 
 Fessenden apparatus is sometimes supplied with a so-called 
 intensity regulator for modifying the intensity of radiation without 
 affecting the frequency. This is for use in communicating with 
 nearby stations. 
 
 Telefunken System. The system designated by this title is the 
 result of an amalgamation of two formerly separate systems of 
 radiotelegraphy. After patent litigation in the German courts, die 
 Gesellschaft fur Drahtlose Telegraphic (Wireless Telegraph Co.) of 
 
 Fig. 59. Fessenden Interference Preventer 
 
 74 
 
SYSTEMS OF RADIOTELEGRAPHY 
 
 75 
 
 Berlin was formed to take over the conflicting interests represented 
 by the Slaby-Arco system and the Braun-Siemens-Halske system. 
 This company is operating under patents granted to Dr. Rudolph 
 Slaby of Berlin, Count Georg von Arco, and Prof. Ferdinand Braun 
 of the University of Strasburg, each of whom has made important 
 contributions to the subject of space telegraphy. The Telefunken 
 system has been developed to a remarkable degree, due largely no 
 doubt to the powerful influence of the German government, and 
 possesses stations all over the world numbering more than 500. 
 
 Fig. 60. Circuit Diagram, Telefunken System 
 
 Their equipment is sold outright and is noted for excellence of work- 
 manship. The earlier sets of apparatus were furnished with a Morse 
 recorder operated by a coherer of the nickel filings type, but latterly 
 an electrolytic detector and head telephone are furnished as a means 
 of reception. As the recorder and associated apparatus cut down 
 the speed of signaling to a degree that seriously impairs their value 
 for commercial work, the employment of the telephone is becoming 
 almost universal practice. The recording mechanism is, however, 
 preferred by many naval authorities over the telephone, as it eliminates 
 the personal equation of the operator and leaves no possibility of 
 error in the received messages. 
 
 A complete wiring diagram of the connections of the Telefunken 
 system is shown in Fig. 60. The aerial is coupled directly onto the 
 
76 
 
 WIRELESS TELEGRAPHY 
 
 AEfl/AL 
 
 closed oscillatory circuit. A small air gap, or cut-out, is located in 
 the transmitting aerial to prevent the received oscillations from flow- 
 ing through the transmitting circuits. Such a gap offers no hin- 
 drance to the high-potential oscillations surging through the radiating 
 circuit of the antennae. Means is shown for adjusting the inductance 
 in the closed circuit of the transmitter, and the inductance between 
 this circuit and the earth. 
 
 The Telefunken Company has more recently announced the 
 so-called singing-spark system of radiotelegraphy, which is based 
 
 on the discovery of Wein that 
 exceedingly powerful discharges, 
 possessing useful properties for 
 radiotelegraphy, may be ob- 
 tained from very short spark 
 gaps. The air gap in this new 
 modification of the Telefunken 
 system is divided between a 
 plurality of copper or silver 
 disks kept apart by rings of 
 mica* This form of oscillation 
 generator is called by the Ger- 
 man firm a quenched spark. 
 When in operation the device 
 gives forth a clear musical tone, 
 which gives the system its name. 
 The detector employed is of 
 special design and said to be 
 more sensitive than the electro- 
 lytic type. It is claimed for 
 the singing-spark system that shorter aerials may be used and that a 
 greater percentage of the energy of the source can be rendered avail- 
 able for radiation; also that the tuning of stations is greatly facilitated. 
 Von Lepel System. It has been claimed by the German ex- 
 perimenter, Von Lepel, that he applied the discovery of Wein to 
 practical radiotelegraphy prior to its adoption by the Telefunken 
 people. However this may be, the discovery referred to seems to be 
 of importance, and though this method of producing oscillations is 
 still in the experimental stage, the system of Von Lepel based thereon 
 
 Fig. 61. Von Lepel Oscillation Generator 
 Circuit 
 
 76 
 
SYSTEMS OF RADIOTELEGRAPHY 
 
 77 
 
 is of interest. The oscillation generator designed by him is shown 
 in Fig. 61. It consists essentially of two copper-box, air-cooled 
 electrodes about 5 inches in diameter, separated by a thin (.002 inch) 
 disk of paper with a J-inch hole, in the center for the spark. The 
 paper serves to keep the arc from running out to the edge of the 
 electrodes. This paper constantly burns away, but a piece will 
 last about three hours. The connections are indicated in the dia- 
 gram, which shows a direct-current generator, but an alternating 
 current will also operate the device. L and L' are inductively coupled 
 inductances, the value of U being very small. The capacity in series 
 with U and bridged across the gap is also very small. A satisfactory 
 explanation accounting for the effects obtained has not yet been put 
 forth. Tests thus far applied to this system have shown advantages 
 not possessed by other systems; but it remains to be seen whether 
 this idea is capable of the extended development it promises. 
 
 Lodge=Muirhead System. Reference has already been made to 
 the great service rendered to the art of radiotelegraphy by Sir 
 Oliver Lodge at that early time 
 when its future depended on the 
 elucidation of obscure theoretical 
 points and on those important 
 practical innovations which could 
 alone make possible a commer- 
 cial development of the idea. 
 Lodge was very early impressed 
 by the fact that periodic currents 
 are amplified under conditions of 
 resonance, and was of the opinion 
 that wireless telegraphy by the 
 early induction method could be 
 facilitated by properly syntoniz- 
 ing the primary and the secondary 
 circuits. He accordingly experimented in this direction and success- 
 fully verified his belief. He soon abandoned the notion of inductive 
 telegraphy, however, and joined forces with Dr. Alexander Muirhead, 
 endeavoring to effect wireless telegraphy by means of Hertzian waves. 
 Always keenly aware of the advantages of syntony between the send- 
 ing and the receiving apparatus, it is not surprising to find that his 
 
 Fig. 62. Lodge Conical Capacity Areas 
 
 77 
 
78 
 
 WIRELESS TELEGRAPHY 
 
 earliest patent specifications were very copious on this point. To 
 facilitate accurate tuning, large conical capacity areas supported by 
 a suitably insulated frame structure were employed, as shown in Fig. 
 62. This form of open oscillatory circuit later evolved into the hori- 
 zontal wire areas now commonly associated with the Lodge-Muirhead 
 system, which is further characterized by being "ungrounded," the 
 lower capacity being in some cases placed several feet above the earth. 
 One form of a Lodge-Muirhead sending and receiving station is 
 diagrammatically represented in Fig. 63, which makes clear the 
 form of capacity areas more recently adopted. The transmitter is 
 a form of direct-coupled closed oscillatory circuit, and the receiving 
 circuit of the closed inductively coupled type. The auxiliary ap- 
 
 Fig. 63. Lodge-Muirhead Sending and Receiving Circuits 
 
 paratus used in conjunction with the Lodge-Mi lirhead steel-disk 
 coherer previously described is not shown in the drawing. Dr. 
 Muirhead, endeavoring to render the system serviceable in connection 
 with the ordinary forms of telegraphic signaling apparatus, has ap- 
 plied a syphon recorder directly connected with the coherer. A 
 Morse register has also been employed, or a telephone, as occasion 
 suggested. Automatic transmission by means of perforated tape is 
 sometimes used, a perforator being furnished with their equipment. 
 The Lodge-Muirhead system has never reached the large indus- 
 trial development achieved by some other systems, notably the Marconi 
 and the Telefunken; but it is, nevertheless, in commercial operation 
 in many parts of the world. Communication was established in 
 1904 between the Andaman Islands and the mainland of Burma, 
 
 78 
 
SYSTEMS OF RADIOTELE GRAPH Y 79 
 
 and has given excellent service since. The distance is slightly over 
 300 miles. The adverse conditions incident to a tropical climate 
 were here admirably met. 
 
 Deforest System. One of the best known American systems is 
 that developed by Dr. Lee DeForest of Chicago. The DeForest 
 interests have many stations located in the eastern States and along 
 the Atlantic seaboard, one of the largest of which, located at Man- 
 hattan Beach near New York City, has successfully effected com- 
 munication with Porto Rico and Colon, Panama, the latter a distance 
 of more than 2,000 miles. A large number of merchant vessels are 
 equipped with this make of apparatus. The United States navy also 
 possesses a number of sets. 
 
 DeForest was among the first to employ an alternating-current 
 transformer to charge the requisite capacity. The earlier form of 
 his apparatus included a small motor-generator set delivering current 
 at 500 volts, which was stepped up to 25,000 to 50,000 volts by means 
 of an oil-immersed transformer, the secondary terminals being con- 
 nected to the aerial and ground with condensers across a gap of the 
 disk type. The receiver circuit used in conjunction with this ap- 
 paratus was of the untuned kind, the detector being of an electrolytic 
 nature called a "goo" responder, an invention of DeForest and 
 E. H. Smythe. A "needle" anti-coherer of extreme simplicity was 
 used with the earlier equipments, consisting of a light steel needle 
 upheld by a retractile spring against two small aluminum rods. A 
 telephone was employed to respond to the fluctuations of current in 
 a local battery circuit caused by the increased resistance of the needle 
 contacts under the action of the received oscillations. Great sim- 
 plicity was aimed at in the design of the entire apparatus. No 
 attempt was made to accomplish selection. 
 
 Electrolytic and thermo-electric detectors have been the subject 
 of extended investigation by DeForest and his co-workers. As a 
 result thereof a detector was evolved, consisting essentially of a small 
 containing vessel filled with a suitable electrolyte into which projects 
 the tip end of an exceedingly fine platinum wire. This "cell," under 
 the influence of oscillations, exhibits a marked difference in its re- 
 sistance to a local current. The similarity to the Fessenden liquid 
 barreter is apparent. Much controversy has arisen relative to the 
 theoretical operation of these detectors, DeForest contending that 
 
 79 
 
80 
 
 WIRELESS TELEGRAPHY 
 
 the action was electrolytic, while Fessenden and others have held to 
 the view that the observed eft'ect was due to the thermal action of the 
 oscillations. Whatever the correct explanation may be, the fact 
 remains that the "electrolytic" detector became, in the hands of 
 DeForest, an exceedingly sensitive device and has contributed largely 
 to the success of his system. 
 
 DeForest later devised a syntonized system based upon the prin- 
 ciple involved in the so-called "Lecher Wires," which reflect waves 
 bearing a definite ratio to the length of such wires. This arrange- 
 ment, exhibiting anti-nodes of potential and current, possesses de- 
 
 Fig. 64. Clark Sending and Receiving Circuits 
 
 cided advantages when applied to the receiving circuit, as it permits 
 a potentially-operable or current-actuated detector to be placed at 
 a point of maximum effectiveness. Possessing also a very definite 
 time-period, this form of circuit was found to lend itself admirably 
 to timing purposes. 
 
 Clark System. The Clark Engineering Company manufac- 
 tures a form of radiotelegraphic apparatus designed by Thomas 
 E. Clark, which is usually supplied as a portable equipment, con- 
 tained in oak cases provided with shoulder straps for carrying. 
 Many such sets have been purchased for the Signal Corps of the 
 
 80 
 
SYSTEMS OF RADIOTELEGRAPHY 
 
 81 
 
 United States army, for which service they are especially intended. 
 The aerial wire is preferably raised by means of a kite. The trans- 
 mitter is of the inductively coupled type, consisting of an induction 
 coil, two one-half gallon Leyden jars, the oscillation transformer, 
 and the necessary auxiliary apparatus, such as secondary batteries, 
 an interrupter, etc. This portion of the equipment is made to be 
 contained in three cases, while the receiving equipment is economic- 
 ally arranged within a fourth oak box covered with canvas. The 
 receptor employed is of the auto-coherer variety, operating under 
 
 Fig. 65. Stone Sending and Receiving Circuits 
 
 the variations of resistance of the imperfect contact between two con- 
 ducting plugs of steel with a small quantity of carbon granules inter- 
 posed between them. A head telephone receiver and one dry- 
 battery cell are shunted around the auto-coherer. The complete 
 sending and receiving circuits of the Clark system are shown in Fig. 
 64. It will be noticed that the system presents nothing of novelty 
 beyond the fact of its admirable adaptability to the requirements of 
 a portable equipment. It can be readily packed on the back of a 
 transport mule, or carried by men in a military campaign. 
 
 81 
 
82 
 
 WIRELESS TELEGRAPHY 
 
 Stone System. Another American system, which is curiously 
 enough little referred to, is the Stone system, invented by J. S. Stone, 
 who has been granted nearly one hundred patents in this country 
 alone, besides their equivalents in European countries. His specifica- 
 tions cover the widest possible range of subjects pertaining to radio- 
 telegraphy and proclaim him to be the possessor of an extraordinary 
 understanding of the more recondite problems connected with the 
 science. Several of his patents cover the inductive coupling of aerials, 
 something after the manner of the Braun-Marconi method. It is 
 
 Fig. 66. Massie Sending and Receiving Circuits 
 
 difficult to believe that any large proportion of the specifications have 
 ever been tried out in practice; in which case they may represent but 
 "anticipatory" patents. One of the Stone arrangements for the 
 sending and receiving stations is shown in Fig. 65, which embodies 
 features of interest particularly from the viewpoint of the "wireless" 
 operator. Reference is made to the multiple function of the send- 
 ing key which allows an operator to be "broken in upon' 'while send- 
 ing, by reason of the fact that the receiving circuit is broken by the 
 depression of the key but instantly closed upon release. The aerial 
 is inductively coupled to the closed oscillatory circuit containing a 
 
SYSTEMS OF RADIOTELEGRAPHY 83 
 
 multiple-spark gap. Various forms of detectors have been used 
 by Stone, especially electrolytic and thermal devices. In one of his 
 patent applications he describes a thermopile of platinum and gold 
 for use as a detector. The Stone system has never been widely 
 exploited although such equipments are occasionally used in this 
 country and doubtless may be found elsewhere. 
 
 Massie System. Walter W. Massie of Providence, R. I., has 
 developed a system of radiotelegraphy which bears his name. While 
 the system has never been exploited on a large scale, numerous sets 
 of apparatus have been purchased by the United States government, 
 and many private concerns find use for this make of apparatus. 
 Massie is well known among the amateur wireless experimenters 
 as the inventor of an exceedingly simple detector of the imperfect 
 contact type, which has rendered many a home-made outfit at least 
 operative where a more complicated receptor would have been pro- 
 hibitive. The device goes under the name of the oscillaphone, and 
 consists simply of a common sewing needle placed carefully across 
 two sharpened carbon edges. A small horseshoe magnet is some- 
 times located under the needle in order to exercise a slight attraction 
 and maintain good connection. In the Massie equipments supplied 
 for long-distance use, an electrolytic detector is employed. The 
 Massie circuits are shown in Fig. 66. The aerial is direct-coupled. 
 
 Poulsen System. A remarkable system due to the genius of 
 Valdemar Poulsen of Copenhagen has of late years attracted great 
 attention, as it undoubtedly marks a decided advance in the art. 
 Poulsen has accomplished by means of a modification in the Duddell 
 arc a method of creating an almost continuous train of undamped 
 oscillations resulting in an equivalent train of electric waves. The 
 ability to generate such a persistent train of waves offers great 
 advantages in the syntonization of stations and in the problem of 
 selective signaling. As before mentioned, the Poulsen system is 
 characterized by the employment of hydrogen under pressure as 
 the surrounding medium for the arc. The receiving device used 
 is the invention of Pederson, and a very full description .of it may be 
 obtained by referring to the Electrician for Nov. 16, 1906. 
 
 Other Systems and Inventors. Numerous other systems of 
 radiotelegraphy have been exploited in various countries, but space 
 will not permit of a detailed description of them here. The patent 
 
 83 
 
84 WIRELESS TELEGRAPHY 
 
 files of every government contain numberless specifications pertain- 
 ing to the art; indeed, it is doubtful if any other improvement in 
 electrical communication has called forth in so short a time a more 
 voluminous patent literature. 
 
 The Rochefort-Tissot system in France has met with considerable 
 success. Perhaps the most distinctive feature of this system is the 
 form of induction coil employed, called a "unipolar transformer." 
 The equipments are manufactured by Ducretet, the French instru- 
 ment maker. 
 
 In Belgium the Guarini system has been installed in various 
 localities with moderate success. The inventor has great faith in 
 the possibility of relaying radiotelegraphic messages to accomplish 
 long-distance transmission. He has devised a relay for such purposes, 
 which seems to promise good results. 
 
 The Russian government has experimented with several sys- 
 tems, but the Popof system is now almost exclusively used. Con- 
 siderable interest attaches to this system on account of its historical 
 importance. As early as 1895, Prof. Popoff communicated to the 
 Physico-Chemical Society of St. Petersburg the details of a device 
 employed by him for graphically registering atmospheric disturbances 
 of an electrical nature by means of a Coherer introduced between an 
 elevated "exploring rod" and the ground. A relay and tapper were 
 also employed, the former serving to operate a Richards register. 
 It is thought by many that sufficient credit is not given Popoff for 
 these innovations. 
 
 Sir H. M. Hozier and S. G. Brown in England have developed 
 a system bearing their names, which differs little from the other 
 systems, with the exception of the detector and method of directly 
 connecting the same to a syphon recorder. The Hozier-Brown 
 detector has been described elsewhere. 
 
 A system of selective signaling which seems to promise well, 
 is that named after the inventor, Anders Bull. Resonance is not 
 employed as a selective agency; instead, the receiver is designed to 
 respond only to a group of wave-trains which are separated by certain 
 unequal and predetermined intervals of time. The mechanism 
 effecting the transmission of such properly timed wave groups is 
 called the dispenser, and the companion device at the receiving end, 
 the function of which is to translate the wave groups into printed 
 
 84 
 
SYSTEMS OF RADIOTELEGRAPHY 85 
 
 Morse characters, is called the collector. Tests conducted by the 
 United States navy with this system were highly satisfactory as re- 
 gards secrecy and freedom from atmospheric disturbances. The 
 complicated nature of the apparatus will possibly prohibit the ex- 
 tensive use of this system, although it possesses advantages not even 
 theoretically possible by resonance alone. 
 
 Conclusion. During the twenty years or so since Hertz made 
 his famous discovery of electric waves, radiotelegraphy has made 
 many substantial advances toward the goal of perfection; and it 
 stands today a conspicuous and brilliant example among the many 
 resources which Science has contributed to modern civilization. 
 Its uses are many and important. To mention its life-saving power 
 alone is to secure for it a high claim to consideration. Its success 
 in this regard has been spectacular in more than one instance; and 
 it is not too much to say that radiotelegraphy has saved hundreds 
 of lives since the "wireless" installation of ships has become prevalent. 
 To travel on the ocean with a "wireless" equipment on board, know- 
 ing that in case of peril the assistance of vessels within a radius of 
 hundreds of miles can be instantly summoned, adds not a little to 
 the comfort and security of the passenger. Radiotelegraphy may 
 indeed be said to have struck a vital blow to the terrors of the sea. 
 The sea, it would seem, has become the chosen sphere of wireless 
 telegraphy, since it fills a want never supplied before. Formerly 
 ocean-bound vessels were isolated from the world for days at a 
 time; but now they can communicate with land or with other ships 
 at almost any point in their course, some of the large ocean liners 
 keeping in such close touch with events that they publish daily bul- 
 letins giving the world's latest news. 
 
 Another startling achievement of radiotelegraphy has been its 
 success in effecting trans-Atlantic communication. Messages are 
 sent between Europe and America across a void of air and water 
 some 3,000 miles in extent. And they are not mere test messages, 
 but regular press telegrams such as might be sent by cable. Here 
 radiotelegraphy has become the direct rival of the old method 
 of wire transmission. Whether the one will ever supersede the other 
 is a question open to debate. The probabilities seem to be in favor 
 of wireless, especially if the present rate of progress continues; but, 
 for the present at least, there is room for both methods. 
 
 85 
 
86 WIRELESS TELEGRAPHY 
 
 Wireless telegraphy promises to be of great service in times of 
 war; in fact, all the leading nations have equipped their armies and 
 navies with radiotelegraphic apparatus. Battleships will have a facil- 
 ity of communication never before possible, and land forces will be 
 equally subserved. Heretofore, one of the first moves of a belligerent 
 force was to cut the enemy's telegraph wires; but to cut off an electric 
 wave will not be such an easy matter. The Japanese constantly 
 made use of wireless telegraphy in the late war with Russia. The 
 Japanese have their own method of effecting radiotelegraphic com- 
 munication, the details of which are kept secret; but that it works 
 successfully, they have well demonstrated. 
 
 Concerning the utility of radiotelegraphy for communicating 
 across land areas, much that is favorable and promising can be 
 recorded; but there is still something to be desired with respect to 
 ease and certainty of operation. The progress thus far made has 
 brought to light many problems which await solution and recorded 
 many phenomena relative to transmission over long distances, espe- 
 cially over land, which cannot as yet be accounted for or controlled. 
 The screening effect of intervening mountains and cliffs exercises 
 a marked difference in the energy of the received signals; long stretches 
 of exceptionally dry ground seern to have the same effect. This 
 probably accounts for the fact that the greatest distances to which 
 signaling has been carried have been over salt water. Signals seem 
 to be more easily effected at night than in daylight; so marked is 
 this effect that communication carried on with perfect success at 
 night has often been permanently interrupted by the advent of day- 
 light only to be resumed the following night. J. J. Thomson has 
 put forward a possible explanation of this, but space forbids its in- 
 clusion here. Again, certain conditions of the atmosphere seem to 
 render but comparatively small energy necessary in the accomplish- 
 ment of long distances at times. 
 
 Thus radiotelegraphy, like all forms of telegraphy, as well as 
 telephony, has its limitations and unsolved problems; but, judging 
 by past achievements, it is not well to dogmatize too emphatically 
 as to the finality of these limits. 
 
 86 
 
THE FIRST S2T OF WIRELESS TELEPHONE INSTRUMENTS FOR 
 
 THE UNITED STATES NAVY 
 
 Installed on the Flagship "Connecticut." The "Audion" Receiver with Tuning Device on 
 the Top at Right, the Transmitter on the Left. 
 
WIRELESS TELEPHONY 
 
 Wireless telephony is not so new almost unborn, indeed 
 as is generally supposed. Like its companion art, wireless teleg- 
 raphy, it began its existence well back in the nineteenth century. 
 Its inception is contemporaneous with that of wire telephony, for 
 Alexander Graham Bell was the originator of both. It is a singular 
 coincidence that Bell, the inventor of the telephone, and Morse, 
 the reputed inventor of the telegraph, should each have been among 
 the first to accomplish their respective modes of communication 
 wirelessly. The history of wireless telephony follows very closely 
 that of wireless telegraphy. The extreme sensitiveness of the tele- 
 phone receiver to small variations of current very naturally sug- 
 gested its employment as a receiving device in connection with the 
 inductive and conductive methods of wireless telegraphy, and 
 attempts were made at an early date to accomplish the transmission 
 of articulate speech by these same means. The results obtained 
 however, were very meager; the inherent difficulties characterizing 
 these methods proved to be even greater with the application of 
 telephone principles, due to the diminution of energy made necessary 
 by the nature of the process. As in the case of wireless telegraphy, 
 the solution of the problem lay in the application of the method of 
 electric radiation. 
 
 Bell's Radiophone. One of the earliest attempts at radioteleph- 
 ony was not of an electrical nature, judging by the usual appear- 
 ances, but depended on the thermal effect of a variable beam of light 
 directed upon bits of burnt cork enclosed in a small glass tube to 
 which was connected a rubber tube to be inserted in the ear of a 
 listener. This device is shown in Fig. 1. The light from a con- 
 venient source was reflected from a thin silvered diaphragm and 
 caused to fall upon the burnt cork. When this diaphragm was set 
 into vibration through the agency of the voice, the light reflected 
 therefrom was subjected to a corresponding variation of intensity, ' 
 and, being directed upon the blackened cork, produced therein 
 minute changes of volume due to the variations of temperature; 
 
 89 
 
2 WIRELESS TELEPHONY 
 
 and such changes produced air-waves which were manifested in 
 the form of sound and audible within the tube. This simple device, 
 invented by Alexander Graham Bell, was called by him a radio- 
 phone. He later greatly improved the apparatus by substituting 
 selenium as the means of reception, the peculiar electrical property 
 of which substance was then first attracting attention. 
 
 Fig. 1. Bell's Kadiophone 
 
 Selenium Cell. In 1873, Willoughby Smith discovered that 
 the resistance of metallic selenium was greatly reduced by exposure 
 to light. The light from a small gas Burner was found to exercise 
 a marked influence on the conductivity of short rods of selenium 
 used as resistances in a series of cable tests then in progress. The 
 discovery caused widespread interest in the scientific world. Among 
 the many men attracted by this peculiar property of selenium was 
 Prof. Bell, who, in conjunction with Sumner Tainter, succeeded 
 in producing the first useful so-called "selenium cell." This de- 
 vice consists essentially of selenium spread over the surface pre- 
 sented by the edges of alternate disks of metal separated by thin 
 sheets of mica after the manner of a condenser, thereby greatly 
 enlarging the area of contact between the selenium and the elec- 
 trodes formed by the alternate disks. By connecting such a cell 
 in series with a battery and telephone receiver, the current passing 
 through the circuit is largely dependent upon the degree of con- 
 ductivity possessed by the selenium cell, which in turn depends upon 
 the amount of light falling thereon. Any variation of the light 
 directed upon the cell is, therefore, capable of causing a correspond- 
 ing variation of the current flowing through the receiver, with the 
 result that such variations become audible therein. 
 
 90 
 
WIRELESS TELEPHONY 3 
 
 Bell's Ph otophone. In 1878 Bell put forward a most ingenious 
 application of the selenium cell for the purposes of radiotelephony, 
 which he called a photophone. The arrangement of apparatus is 
 shown in Fig. 2. The selenium cell C is placed in the focus of a 
 parabolic reflector R and is thus interposed in the path of the rays 
 reflected by the mirrored surface of a diaphragm D from any 
 suitable source of light S. The resistance of the selenium cell 
 was approximately 1,200 ohms in darkness, and about half that 
 when fully illuminated. The mode of speech-transmission is so 
 similar to that of the radiophone that further description is not 
 necessary. 
 
 The photophone, as proposed by Bell, may be made to trans- 
 mit speech perfectly over short distances, but it is obviously limited 
 by reason of the inefficient means employed to effect the variation 
 of the intensity of a source of light. As the employment 
 
 SOURCE 
 
 B 
 \1 
 TFfY LJ, 
 
 'I - *[ 
 
 ffZCE/VZft 
 
 BA TTFfY 
 
 ' 
 
 Fig. 2. Bell's Photophone 
 
 of the device for distances relatively long necessitated the use of 
 powerful sources of light and adequate means for controlling the 
 same, the invention remained but a beautiful laboratory experiment 
 until the discovery of the speaking arc by Simon in 1897 opened up 
 the possibility of future development. 
 
 "Light Telephony." Prof. H. T. Simon of the Physical Institute 
 of the University of Erlangen discovered, toward the end of the year 
 1897. that a direct-current arc may be made to give forth musical 
 tones and even speech by superimposing a telephonic voice current; 
 upon the arc current. This discovery suggested the possibility of 
 using' Simon's arc as a transmitting arrangement 01 the BeJtl photo- 
 
 91 
 
4 WIRELESS TELEPHONY 
 
 phone. With this end in view, numerous experiments were carried 
 on, principally in Germany, aiming to increase the efficiency of the 
 apparatus when operated in conjunction with powerful search- 
 lights, and also to develop the selenium cell to a point of greater 
 sensitiveness. Wireless telephonic communication by this means 
 has become known as light telephony, and has reached its highest 
 development in the hands of that most ingenious German investigator, 
 Ernst Ruhmer. The German navy has several vessels equipped 
 with the Ruhmer apparatus for intercommunication. It is said that 
 a distance of twenty miles is, under favorable weather conditions, the 
 limit of operativeness with this form of radiotelephony. The use 
 of the system is necessarily restricted to open spaces, and dependent 
 upon clear atmosphere. 
 
 Telephony by Means of Hertzian Waves. The success achieved 
 by Marconi in telegraphing without wires inspired many investigators 
 to apply the Hertzian-wave method to the problem of telephony. 
 As early as 1897 various workers became imbued with the idea and, 
 as a result, a number of systems of radiotelephony have grown up 
 contemporaneously with those of radiotelegraphy. It cannot be 
 said, however, that the results accomplished by the early experi- 
 menters in this field gave more than a promise of future usefulness 
 for this method of communication, the distances covered being ex- 
 tremely small in proportion to the complexity of the apparatus in- 
 volved. In many instances, however, the inventors of such systems 
 Jiad a clear perception of the fundamental requirements, and felt 
 confident that the development of the art on its practical side 
 would ultimately make possible a successful application of their 
 theories. 
 
 The principal difficulty encountered in the application of Hertzian 
 waves to the problems of telephony was found at the start to reside 
 in the transmitting portion of the apparatus. The receiving end 
 offered no great obstacle, since it was known at an early date that 
 many of the detectors used in connection with radiotelegraphy would 
 prove suitable for the reception of speech providing that a means 
 could be discovered to effect the emission of wave-trains whose 
 energy should vary in accordance with the vibrations of the human 
 voice. The fundamental problem of radiotelephony is practically 
 the same as that met with in ordinary wire telephony to cause a 
 
 92 
 
WIRELESS TELEPHONY 5 
 
 distant diaphragm to repeat sympathetically the vibrations of a dia- 
 phragm against which the energy of the sounds to be transmitted is 
 directed. In both cases the efficiency of the various transformations 
 of energy involved in the process is of prime importance. The 
 current-carrying capacity of the carbon transmitter places a limit on 
 the amount of energy possible to utilize telephonically. This restric- 
 tion is felt to a marked degree when the device is associated with 
 the necessarily large amount of energy required for Hertzian-wave 
 radiation over any considerable distance. In view of the foregoing, 
 it is not surprising to find that early experiments in radiotelephony 
 were directed almost exclusively toward a solution of the problem of 
 an efficient transmitting apparatus. 
 
 Many attempts were made to accomplish this end by placing 
 the ordinary microphone transmitter in the primary of an induc- 
 tion coil, thus serving the purpose of an interrupter, as exemplified 
 in Dolbear's early wireless telegraph system. Such experiments 
 only sufficed to show that nothing was to be gained in this way, 
 largely by reason of the before-mentioned inherent limitations of 
 the telephone transmitter. The problem was then attacked in 
 another manner, viz, by endeavoring to modify telephonically a train 
 of waves of a constant intermittency radiating from a continuously 
 operating source of oscillations, such, for instance, as a simple radio- 
 telegraphic transmitter without a primary signaling key. Though 
 this method allowed a much greater amount of energy to be utilized, 
 it soon became evident that a grave difficulty was presented due 
 to the nature of the radiations from such an arrangement. The 
 train of waves thus generated is not continuous, but consists of 
 intermittent wave-trains separated by short periods of time during 
 which no radiation takes place. These breaks in the continuity 
 of the train are often of greater duration than the individual oscilla- 
 tions due to one complete discharge of the condenser; they conse- 
 quently produce in the telephone receiver a continuous buzz which 
 seriously interferes with the audibility of the received voice vibrations. 
 As the timbre of the human voice depends upon overtones and upper 
 harmonies of a frequency of from 5,000 to 8,000 or more, the pauses 
 between ' oscillation trains also interfere with clear articulation 
 whenever their frequency drops much below 10,000 per second. 
 At frequencies of from 20,000 to 50,000, however, this feature ceases 
 
 93 
 
6 
 
 WIRELESS TELEPHONY 
 
 to be a hindrance. The success of the method of telephonically 
 varying the energy emitted from a continuously operating source of 
 radiation was seen, therefore, to depend upon the possibility of pro- 
 ducing more perfectly sustained oscillations of high frequency. 
 The means for creating oscillations that are undamped and prac- 
 tically continuous, may be considered the greatest problem of radio- 
 telephony relative to transmission. At the present time there are 
 two methods of accomplishing such persistent radiations, viz, by 
 employing the high-frequency alternator, or by using some form of 
 the oscillating arc. The last-named method has been developed, 
 under the ministrations of Valdemar Poulsen, to a degree of efficiency 
 that promises to place radiotelephony on a commercial basis. The 
 alternator method has been persistently favored by Prof. il. A. Fes- 
 senden, who has accomplished some remarkable results. Both 
 methods have their staunch advocates, each possessing its own peculiar 
 advantages as well as limitations. 
 
 Nature of a High=Frequency Telephone Current. The foregoing 
 paragraphs have indicated briefly the general theory upon which the 
 
 posmvr 
 
 Fig. 3. Diagram Representing High-Frequency Current 
 
 most successful systems of radiotelephony have been developed. It 
 remains to consider in more detail the nature of the action involved 
 when a uniform flow of undamped oscillations is modified by the va- 
 riations of a voice current. 
 
 It is convenient for a ready understanding of the matter to first 
 consider the case of a high-frequency alternator supplying a con- 
 stant alternating current of a periodicity somewhat above human 
 audibility say 50,000 cycles per second. Supposing such a current 
 to be flowing through a variable resistance such as a telephone trans- 
 mitter, the effect of an increase of the resistance thereof manifests 
 itself by a lessening of the amplitude of each individual half-wave 
 of current; while, conversely, a decrease of the resistance manifests 
 itself by an amplification of the current half-waves. When, there- 
 
 94 
 
WIRELESS TELEPHONY 7 
 
 fore, the resistance is made to vary with great rapidity, as when the 
 diaphragm of the transmitter is thrown into vibration by sound, 
 the effect upon the alternating current flowing therein is to produce 
 a corresponding change in the maxii um value of each half-wave. 
 
 Fig. 4. Diagram Kepresenting Variations of Amplitude 
 
 As the energy of each half-wave may be represented by its ampli- 
 tude, it is evident that an alternating current varying in this manner 
 exhibits a wave-form of energy equivalent in many respects to a direct 
 current similarly modified. Figs. 3 and 4 illustrate this idea, Fig. 3 
 representing the steady alternating current permitted by the normal 
 resistance of a transmitter; and Fig. 4 showing the alterations of 
 amplitude thereof occasioned by the variations of resistance in the 
 said transmitter. It will be noticed that the maximum instan- 
 taneous values may be greater than normal, as well as less, due to 
 the fact that the resistance of a transmitter when spoken into varies 
 between limits above and below its resistance when at rest. Some 
 idea of the complexity of the action taking place under the conditions 
 of actual practice may be had by referring to the wave-form shown 
 in Fig. 5, which represents the current curve, or oscillagram, of a 
 
 Fig. 5. Oscillagram of a Telephone Current 
 
 telephone current produced by the vowel, long 6, spoken into the 
 transmitter. In forming a mental conception of the wave-form 
 resulting from the superimposing of a telephonic voice current upon 
 a high-frequency oscillating current, the enormous difference in 
 their respective periodicities must be borne in mind. 
 
 95 
 
8 WIRELESS TELEPHONY 
 
 In the case of an oscillation generating arrangement which does 
 not produce a perfectly sustained train of electric waves but a series 
 of partially damped wave-trains separated by slight breaks of con- 
 tinuity, the essential conditio i for success in connection with radio- 
 telephonic work is that the ii terruptions shall not take place at an 
 audible frequency. It is highly probable that the direct-current 
 arc method of creating oscillations does not produce an absolutely 
 continuous train of waves, as is the case with a high-frequency alter- 
 nator, but, on the contrary, is made up of a great number of groups 
 of almost undamped oscillations separated by an interval of time, 
 very small even in comparison with the duration of each group. 
 
 Oscillation Generators. An account has already been given, 
 in the pages devoted to Radiotelegraphy, of the attempts which 
 have been made to construct high-frequency alternators for use in 
 the production of continuous, undamped oscillations, and some 
 description given of such machines. Reference has also been made 
 to the development of the direct-current arc method of producing 
 a similar result. In the present instance it is not deemed necessary 
 to dwell on these subjects further than to give some notion of the 
 particular devices constructed for use ^n connection with the mcst 
 successful systems of radiotelephony, and to mention those modi- 
 fications of the arc method which have been found to give the best 
 results in this field of use. 
 
 Undoubtedly the most successful high-frequency alternators 
 have been those constructed by Prof. Fessenden for use in his ex- 
 tensive experiments in radiotelephony carried on at the Brant Rock 
 (Mass.) Station of the National Electric Signaling Company. This 
 inventor has devised several such machines, one of them having an 
 output of 2 kilowatts operating at 80,000 cycles, and a voltage of 
 225 volts. This machine was of the double armature type with 
 300 teeth on each, direct-coupled to a DeLeval turbine. A similar 
 generator designed for use on shipboard and run by a turbine is 
 capable of developing 3 kilowatts at a frequency of about 100,000 
 cycles. Fessenden has also designed a 10-kilowatt machine of a 
 periodicity of 100,000 per second. The problem of properly design- 
 ing such generating units and constructing them on a commercial 
 basis cannot as yet be said to be satisfactorily solved; it is generally 
 felt, however, that the solution of the problem will be effected at no 
 
 96 
 
WIRELESS TELEPHONY 9 
 
 distant date, at which time this method of producing the requisite 
 oscillations for electric-wave communication will supersede in many 
 instances the more complicated and less constant methods now in use. 
 
 There are in use at the present time various arrangements of 
 the direct-current arc employed as a means of creating alternating 
 currents of great frequency, all of which depend for their operation 
 upon the principle of the Duddell arc but differing in the details 
 of application. One of the earliest and most successful of these is 
 due to Poulsen, who achieves extremely high-frequency oscillations 
 of great energy by causing the arc to take place between copper and 
 carbon electrodes enclosed in a chamber containing hydrocarbon 
 gas. In order to increase the energy of radiation, Poulsen later 
 employed several arcs in series. This is known as the multiple-arc 
 system, and has been developed to a high degree by die Gesellschaft 
 fur Drahtlose Telegraphic of Berlin. 
 
 Telephonic Control of Oscillations. Radiotelephony figuratively 
 substitutes in place of the metallic line of ordinary telephone prac- 
 tice a continuous stream of electric waves of approximately uniform 
 strength. By varying from instant to instant the energy of this 
 stream of waves in accordance with the variations of air-pressure 
 acting against a transmitting diaphragm, a transference of such 
 energy-variations is effected between two stations. By the employ- 
 ment of suitable translating devices, the energy-vibrations of the 
 wave-stream may be made to undergo a transformation resulting 
 in the movement of a second diaphragm which exactly duplicates 
 the vibrations of the first, and the variations of air-pressure occasioned 
 thereby complete the cycle of energy-transformations from sound 
 to sound. 
 
 It is to be noted in connection with the foregoing analysis that 
 it is not the entire amount of energy of the flow of waves between 
 stations that is available for transformation into sound at the receiv- 
 ing end, but only the energy represented by the variations of this 
 flow of waves. Thus the problem of telephonically controlling a 
 large amount of energy for efficient radiotelephonic transmission 
 is to effect, by means of the energy of the voice vibrations, a maximum 
 percentage of variation in the energy radiated. With the methods 
 employed at the present time there are reasons for believing that this 
 percentage does not greatly exceed 5 to 8 per cent of the total energy. 
 
 97 
 
10 WIRELESS TELEPHONY 
 
 In this respect radiotelephony differs very widely from radioteleg- 
 raphy, for with the latter the entire energy of radiation is available 
 to the limit of our ability to detect it. Some of the inventors claim 
 a greater percentage of efficiency for their respective systems of radio- 
 telephony. Fessenden has devised an improved form of transmitter 
 which he states produces much better results. 
 
 There are several ways .of modifying the electric oscillations 
 set up in a transmitting arrangement for the purposes of radio- 
 telephony. The method generally employed involves the use of 
 some form of carbon transmitter whereby the 
 variations of its resistance under the influence of 
 the energy of the voice are made to vary the os- 
 cillatory current directly, or a local-battery circuit 
 similarly affected is inductively associated with 
 the oscillatory circuit. Variations in the emitted 
 wave-train may also be accomplished by the use 
 of a condenser transmitter formed by a thin me- 
 tallic diaphragm separated from a metallic plate 
 by a thin layer of air acting as dielectric, the 
 vibrations of said diaphragm producing variations 
 of capacity between the two surfaces. This vari- 
 able capacity is used to throw the aerial in and 
 out of tune. The inductance of an oscillatory 
 F Fessenden I circu?t f circuit may also be made to vary by means of 
 the voice and produce a like result. One of the 
 earliest suggestions relating to the telephonic control of the energy 
 of oscillations was made by an Italian, Lonardi, who, in 1897, pro- 
 posed that the spark balls of a Righi oscillator connected to a source 
 of constant potential be made to vibrate by the voice, thereby alter- 
 ing the length of the spark gap and causing the oscillator to be 
 charged to greater or lesser potentials, and thus varying the energy of 
 the emitted waves. 
 
 Transmitting Circuits. One of the simplest and earliest cir- 
 cuits patented for use in connection with radiotelephony is 
 shown in Fig. 6. It is due to Fessenden, and consists of a high- 
 frequency alternator connected in series with an aerial, a telephone 
 transmitter, and the ground. The time-period of the radiating cir- 
 cuit thus formed is adjusted to the periodicity of the dynamo. 
 
 98 
 
WIRELESS TELEPHONY 
 
 11 
 
 AERIAL 
 
 TK/WSM/TTER. 
 
 The patent application on this arrangement was filed in 1901 at a 
 time when it is generally believed that the creation of electric waves 
 necessitated an abrupt release of energy, as 
 exhibited by the discharge of a condenser. 
 In experiments carried on with this arrange- 
 ment in 1906, a distance of about ten miles 
 was covered, the generator running at 10,000 
 revolutions per minute and developing 50 
 watts at 80,000 cycles per second. The 
 resistance of the armature was about 6 
 ohms. An electrolytic cell was used for a 
 detector. 
 
 Another method of effecting the tele- 
 phonic variation of an oscillatory system is 
 shown in Fig. 7. The aerial is connected to 
 the secondary of a small transformer, the 
 primary winding of the same being in- 
 cluded in a local-battery transmitter cir- 
 cuit. 
 
 An arrangement for use with the arc form of oscillation generator 
 is shown in Fig. 8. Direct current for the arc is supplied to the 
 terminals of the closed oscillating circuit through the secondary of 
 
 Fig. 7. Transmitter Induc- 
 tively Associated with Aerial 
 
 Fig 8. Transmitter Associated with the Supply Circuit 
 
 a transformer, the primary circuit of which contains a carbon trans- 
 mitter and local battery. The fluctuations of intensity of the oscil- 
 lations may be, effected in a manner diagrammatically shown in 
 
 99 
 
12 
 
 WIRELESS TELEPHONY 
 
 Fig. 9, where the inductive method of superimposing the telephone 
 current from a local circuit is applied directly to the closed oscilla- 
 tory circuit. Inductances I and I' inserted in the supply mains 
 
 EARTH 
 
 Fig. 9. Transmitter Inductively Associated with the Closed 
 Oscillatory Circuit 
 
 prevent the voice current from passing around through the source 
 of supply. 
 
 In Fig. 10 is shown still another method of locating the variable- 
 resistance member, viz, by shunting the" secondary of the oscillation 
 
 AERIAL 
 
 EAffTH 
 
 Fig. 10. Transmitter Shunted across the Aerial Inductance 
 
 transformer employed in connection with an inductively coupled 
 aerial. The telephone transmitter may also be used with a directly 
 coupled aerial by causing it to vary the effective turns of a portion 
 of the inductance included in the open radiating circuit, as in Fig. 11. 
 
 100 
 
WIRELESS TELEPHONY 
 
 13 
 
 From the circuits here given, it is evident that the conditions 
 essential to telephony are fulfilled when the transmitter is so placed 
 as to produce by its action a change of the electrical properties of 
 the radiating aerial; and experience has shown that this may be 
 accomplished with the microphonic, or carbon, transmitter in a 
 variety of ways, many of which seem to operate with equally good 
 effect. The condenser, or variable-capacity, transmitter is effectively 
 operative only in conjunction with the oscillatory portions of the 
 sending circuit, usually as a shunt. One method of placing this form 
 
 ARC 
 
 EARTH 
 
 Fig. 11. Transmitter Shunted across a Portion of the 
 Aerial Inductance 
 
 of transmitter is shown in Fig. 12, which arrangement has been em- 
 ployed by Fessenden. ," 
 
 As before remarked, the small current-carrying capacity of the 
 microphonic transmitter has proved to be a great obstacle to the 
 rapid development of the art of radiotelephony as a commercial 
 proposition; and it may be said that until an efficient means is de- 
 vised for overcoming this difficulty, and thereby greatly increasing 
 the percentage of variation in the intensity of the oscillations, or 
 the equivalent thereof, the sphere of usefulness for this form of 
 wireless communication will be much restricted. Many attempts 
 have been made to effect this improvement by connecting several 
 transmitters in multiple to be acted on by a common mouthpiece. 
 Various so-called telephonic repeaters have also been devised pur- 
 porting to accomplish an increase in the amplitude of the telephonic 
 
 101 
 
14 
 
 WIRELESS TELEPHONY 
 
 AER/AL 
 
 CONDENSER 
 TRANSMITTER* 
 
 current Such devices, however, have not proved to be a satisfac- 
 tory solution of the problem, although Fessenden claims to be able 
 to effect a decided amplification with an instrument of the latter 
 character designed by himself. This ingenious investigator has 
 
 undoubtedly constructed an instrument 
 more nearly fulfilling the requirements 
 of a transmitter adapted to this class of 
 work than any heretofore presented. It 
 is called by him a "trough" transmitter, 
 and is said to be able to carry continu- 
 ously more than 10 amperes. The elec- 
 trodes are water-jacketed The amount 
 of variation in a current of this magni- 
 tude, produced by the action of the voice, 
 is of course the important factor. The 
 results accomplished by the "trough" 
 transmitter indicate a decided gain over 
 the form commonly employed. Further 
 radical improvements in transmitter de- 
 sign may be confidently expected from 
 the numerous experimenters whose irtventive ability is now being 
 brought to bear on the problem. 
 
 Receiving Arrangements. For purposes of radiotelephony the 
 detectors depending upon mere potential for their operation, such as 
 the early forms of coherer, are practically useless. The essential 
 characteristic which a detector suitable for this class of work must 
 possess is that it shall not only respond to the received oscillations, 
 but that it shall be affected to a certain extent in proportion to the 
 amplitude of such oscillations. In short, radiotelephony requires 
 a form of detector which is quantitative, that is, one which will 
 respond to the varying integral value of the oscillating current. 
 Such devices as the thermo-electric, electrolytic, ionized gas, and 
 crystal-valve detectors are all of this type, and may be used for the 
 reception of speech when properly connected with a telephone re- 
 ceiver. This quantitative function may be elucidated by consider- 
 ing the action of a thermo-electric detector properly associated with 
 a tuned receiving circuit. If a continuous train of undamped waves 
 falls upon the aerial, their effect on the detector is to increase its 
 
 Fig. 12. Condenser Transmitter 
 
 102 
 
WIRELESS TELEPHONY 
 
 15 
 
 resistance by raising its temperature, and thereby decrease the 
 amount of current flowing through the telephone receiver. As long 
 as the flow of such waves remains constant, their heating effect upon 
 the fine platinum wire of the detector, and consequently its resist- 
 ance, remains constant, and no sound is heard in the receiver. If, 
 however, the wave-train which strikes the aerial be of a fluctuating 
 nature, due to the vibrations of the distant telephone transmitter, 
 the variations of amplitude of the received oscillations will cause a 
 corresponding variation in their heating effect on the platinum wire, 
 accompanied by like variations in its resistance, whereupon the 
 current flowing through the telephone receiver will be similarly 
 varied, with the result that the diaphragm is thrown into vibrations 
 exactly imitating the movement of the transmitting diaphragm. 
 
 There have been pre- 
 viously described under the 
 head of radiotelegraphic de- 
 tectors almost all the devices 
 used for a similar purpose 
 in connection with radio- 
 telephony. In view thereof 
 it is not thought necessary 
 to devote more space to the 
 subject here, further than 
 to call attention to a form 
 of telephone receiver in- 
 vented by Fessenden and 
 called by him a "hetero- 
 dyne" receiver, a most ingenious application of the Bell instrument 
 to the purposes of space telephony. The device consists of two small 
 coils of wire, one of which is wound upon a stationary laminated 
 core composed of very fine soft-iron wires; the second coil, held in 
 close proximity to, and co-axial with, the first, is attached to the center 
 of a thin mica diaphragm. A high-frequency current from a local 
 source is maintained through the stationary coil. The other coil, ar- 
 ranged to vibrate with the diaphragm, is connected in the receiving 
 oscillation circuit, as shown in Fig. 13. The periodicity of the local 
 alternating current is adjusted to approximately the same frequency 
 as the received waves, thereby creating a mechanical force exerted be- 
 
 Fig. 13. Heterodyne Receiver Circuit 
 
 103 
 
16 WIRELESS TELEPHONY 
 
 tween the two coils a force which varies with every fluctuation of the 
 intensity of the received oscillations, and results in vibrations of the 
 mica diaphragm corresponding to those of the distant transmitter. 
 When this device is used as a detector in connection with radio- 
 telegraphy, the frequency of the local source of current is purposely 
 made to be slightly different from the frequency of the received oscil- 
 lations; under which condition the physical phenomenon known as 
 ''beats" is engendered. This is due to the fact that at certain equal 
 intervals the two wave-form currents agree in phase and reinforce 
 each other, while at times midway between two such successive 
 agreements they are opposite in phase and tend to neutralize each 
 other. These intervals of maximum reinforcement occurring at an 
 audible frequency produce in the receiver a musical note of a 
 duration depending upon the length of the Morse dot or dash. 
 By means of this simple process, it is, therefore, possible to pro- 
 duce audible tones by the interaction of two alternating currents 
 whose respective frequencies are far above audibility. The het- 
 erodyne receiver is almost entirely unaffected by atmospheric 
 disturbances, and seems to offer exceptional possibilities in con- 
 nection with multiplex transmission, as well as selective communica- 
 tion. 
 
 Two=Way Transmission. In wire telephony simultaneous talk- 
 ing and listening is possible by reason of the simple nature of the 
 circuits and because of the comparatively small amount of energy 
 involved in telephonic transmission. Radiotelephony presents in 
 this regard difficulties which tax to the utmost present inventive 
 ability. Without special appliances it is of course necessary after 
 talking to throw over a listening key or switch in order to receive the 
 reply. The introduction of this manual operation, while not of a 
 nature to greatly detract from the usefulness of this method of com- 
 munication, interferes to an appreciable extent with that ease of 
 operation we are accustomed to associate with the telephone, and 
 destroys the illusion of the actual presence of the person spoken to. 
 It cannot well be expected in an art so young that minor details of 
 this nature should have been thoroughly perfected. Arrangements 
 for simultaneous talking and listening have already been put for- 
 ward, and some have met with more or less practical success. Fes- 
 senden has patented several such devices one involves the use of 
 
 104 
 
WIRELESS TELEPHONY 17 
 
 a commutator which connects the transmitter and receiver to the 
 aerial in very rapid alternation; another and a more practicable method 
 is called by him the "balance" method, and consists in the applica- 
 tion of the "bridge" together with a "differential" arrangement often 
 employed in duplex telegraphy, the complete circuit requiring a 
 "phantom," or artificial, aerial. The detector is unresponsive to the 
 powerful oscillations emanating from the same station, but sensitive 
 to the oscillations from the distant station. This "balance" method 
 materially cuts down the loudness of the received sounds. 
 
 Radiotelephonic "calling" is accomplished by radiotelegraphic 
 methods. A coherer associated with a local battery and relay is 
 sometimes employed to ring an electric call bell. In such cases it 
 is necessary to provide means for cutting out the coherer and relay 
 during conversation. Under conditions where it is impractical to 
 achieve the operation of a relay, it becomes necessary to keep an 
 operator on duty "listening in." 
 
 Systems of Radiotelephony. Radiotelephony undoubtedly pos- 
 sesses many advantages over radiotelegraphy, not the least of which 
 is the fact that a skilled operator is not required to translate the 
 dot-and-dash signals. The transmission of intelligence is more 
 direct and expeditious, and in times of emergency this might become 
 an advantage of great importance. No form of communication is 
 so satisfying as that of speech. It is due to this fact, perhaps, that 
 ordinary wire telephony stands today superior to the older art of 
 telegraphy in point of development. The future may record a 
 similarly greater development of radiotelephony than will be ac- 
 corded to its companion art; but at the present time it cannot 
 be said to compare with radiotelegraphy as regards efficiency and 
 simplicity of apparatus. Its weak points are known and under- 
 stood, however, and every effort is being made to remove the ob- 
 stacles that stand in the way of a more efficient utilization of the 
 means employed. 
 
 While still susceptible of great improvement, and in many 
 cases requiring a multiplicity of complicated apparatus, there are 
 a number of radiotelephonic systems which have been exploited in 
 the various countries, many of which are in regular service. Nearly 
 all of the large navies of the world are supplied with equipment for 
 intercommunication between the different vessels of a fleet. Among 
 
 105 
 
18 
 
 WIRELESS TELEPHONY 
 
 the most successful systems may be mentioned the Telefunken and 
 Ruhmer systems in Germany, the Poulsen system in Denmark, 
 the Marjorana system in Italy, and in America the systems developed 
 by Fessenden, DeForest, and Collins. Many other systems are 
 known, but they exist in a more or less imperfect state of develop- 
 ment. 
 
 Telefunken System. Die Gesellschaft fur Drahtlose Tele- 
 graphic of Berlin has put forward one of the most thoroughly de- 
 veloped systems of radiotelephony in commercial operation at the 
 present time. It is generally known as the Telefunken system, 
 which is the name applied to the radiotelegraphic system operated 
 by the same company. 
 
 The Telefunken radiotelephonic system is of the oscillating-arc 
 type. The arrangement of circuits is shown in Fig. 14. Six or 
 
 CHOKE CO/L^ 
 
 Fig. 14. Transmitter Circuit of the Telefunken System 
 
 twelve electric arcs, connected in series and shunted by an inductance 
 and capacity, form the source of the high-frequency oscillations. 
 The energy supplied to this portion of the circuit is derived from 
 a direct-current source of 220 or 440 volts (if the latter, 12 arcs in 
 series are used) connected through a rheostat, an ammeter, and a choke 
 coil. The choke coil is used to prevent the oscillatory current from 
 passing through the dynamo. A hot-wire ammeter is included in the 
 oscillatory circuit, and another between the aerial and the ground, 
 
 106 
 
WIRELESS TELEPHONY 
 
 19 
 
 used for tuning purposes. When the circuits are in exact resonance, 
 these instruments give a maximum reading, thus affording a very 
 convenient means of ascertaining if the system is in proper adjust- 
 ment at any time. An adjustable condenser is provided in the oscil- 
 latory circuit, and a variable inductance in the aerial, to facilitate 
 tuning. It will be noted that the carbon transmitter is associated 
 with the aerial as a shunt around the secondary 
 of the oscillation transformer. An ordinary 
 transmitter is used and, in practice, means are 
 provided for opening the transmitter circuit 
 while calling, and at other times when it is de- 
 sired to protect the transmitter from the detri- 
 mental effects of continued exposure to the 
 heavy current. 
 
 The electrodes employed for the arcs in 
 this system possess features of interest. The 
 positive member is formed by a copper tube 
 about 2J inches in diameter and 8 inches long 
 closed at the bottom by a concave piece of the 
 same material. The internal cavity is filled 
 with water, thus serving to keep the metal cool. 
 Fig. 15, which shows the Telefunken electrodes, 
 represents the positive member as partially cut 
 away in order to make clear the construction. The negative elec- 
 trode is of carbon \\ inches in diameter, set well up in the con- 
 cave portion of the positive electrode, but separated therefrom by 
 a gap of about \ inch. The arc formed between these two mem- 
 bers tends to maintain the uniformity of the gap. It is claimed 
 that the consumption of carbon is only about 1 inch in nearly 300 
 hours, and that the copper electrode is not appreciably affected 
 by the arc. The water is changed as often as required, according 
 to the time it is subjected to the heat of the arc, or by reason of 
 evaporation. Means are provided for the adjustment of each in- 
 dividual arc, and for the simultaneous striking of all. The fre- 
 quency usually achieved by this method is approximately 375,000 
 cycles per second. The equipments are rated something under one 
 kilowatt for connection with 220 volts. 
 
 The receiving arrangement used with this system is of the 
 
 Fig. 1 5. Telefunken 
 Electrodes 
 
 107 
 
20 
 
 WIRELESS TELEPHONY 
 
 simplest kind, consisting of a detector (electrolytic or thermo-electric) 
 and telephone directly coupled to the aerial, such as are commonly 
 employed with radiotelegraphy. The entire apparatus is very com- 
 pact, requiring but little space, and may be conveniently placed on 
 a small table. A distance of 25 to 45 miles may be very well covered 
 with the Telefunken sets such as are supplied for use on shipboard, 
 and equipments of greater power may be had. Simultaneous talking 
 and receiving is not provided for in this system. 
 
 Ruhmer System. The system due to Ernst Ruhmer, the Ger- 
 man investigator, well known for his extensive work in connection 
 with the development of "light telephony" and for his researches 
 
 Fig. 16. Circuits of Ruhmer System 
 
 into the properties of selenium, is characterized by the use of an 
 oscillatory arc burning in hydrogen or other suitable gas. The 
 Ruhmer circuits are shown in Fig. 16. A local-battery transmitter 
 circuit is employed to superimpose, by means of an induction coil, 
 the voice current upon the supply terminals of the oscillatory portion 
 of the arrangement. A direct-current dynamo of 440-volt pressure 
 is used. The transmitting aerial is inductively coupled to the closed 
 oscillation circuit. Many different forms of arc have been experi- 
 mented with by this inventor, some with a magnetic blow-out. Sim- 
 plicity of apparatus has been aimed at. The receiving arrangement 
 consists of an electrolytic detector, battery, and telephone receiver 
 
 108 
 
WIRELESS TELEPHONY 
 
 21 
 
 connected with the aerial and its associated capacity and inductance. 
 By using fairly low antennae, the Ruhmer system has operated very 
 successfully over comparatively short distances. 
 
 Poulsen System. Special interest attaches to the Poulsen system 
 by reason of the fact that the development of the arc method of pro- 
 ducing sustained high-frequency oscillations was largely due to the 
 initiative of this investigator. Mention was made of the Poulsen 
 modification of the singing arc in its application to radiotelegraphy. 
 Fig. 17 represents diagrammatically its application to a system of 
 radiotelephony. A direct current from a suitable source is applied 
 to the terminals of the arc through the secondary of a small trans- 
 
 Fig. 17. Circuits of Poulsen System 
 
 former, in the primary of which is placed a local battery and tele- 
 phone transmitter. The aerial is directly coupled, and two oil- 
 condensers are so located as to prevent the direct current from 
 reaching the aerial or ground. The magnetic blow-out devices 
 are not shown in the cut. At the receiving station the aerial is in- 
 ductively coupled with a closed oscillatory circuit w r hich is connected 
 with a local-battery circuit containing the detector and a telephone 
 receiver. 
 
 Poulsen has constructed many forms of the copper-carbon arc 
 burning in a magnetic field in an atmosphere of gas. In order to 
 meet the difficulties caused by the irregularity of action due to the 
 
 109 
 
22 WIRELESS TELEPHONY 
 
 unequal burning of the carbon, he employs in connection with one 
 form of his arc a cylindrical carbon electrode of large diameter 
 which is slowly rotated, thus presenting constantly a new surface for 
 the arc. In another modification, the same result is accomplished 
 by means of a rotary magnetic field which acts directly on the arc, 
 causing the latter to constantly change its position on the surface of 
 the electrodes. He has also employed various gases through which 
 the arc is maintained. In the commercial equipments more 
 recently put out, the gas is supplied by alcohol allowed to drip 
 slowly into the arc chamber, at a rate of about one drop every 
 half second. 
 
 The transmitter employed by Poulsen is essentially the common 
 carbon-granule device; he has, however, effected the variation of his 
 oscillations by means of a multiple transmitter consisting of seven or 
 eight such instruments connected in multiple and arranged to be 
 acted upon by one mouthpiece. 
 
 Successful telephonic communication has been accomplished 
 over distances varying from a few miles up to three hundred. Poulsen 
 long-distance stations are located at Lyngby, Denmark; at Berlin, 
 Germany; and at Cullercoats near Newcastle, England; and smaller 
 stations are % located in Denmark and elsewhere. The aerial used at 
 Lyngby for long-distance transmission is about 225 feet high, and 
 is of the umbrella type composed of 24 strands of phosphor-bronze 
 wire. A 20-horse-power gasoline engine operates a 10-kilowatt, 
 500-volt, direct-current dynamo for the arc. A phonograph record 
 has been transmitted from this station to Berlin and distinctly heard 
 there a distance of 325 miles. 
 
 The Marjorana System. In Italy radiotelephonic experiments 
 have been carried on by Prof. Quirino Marjorana, resulting in the 
 successful transmission of the voice from Rome to Messina, a dis- 
 tance of about 312 miles. As a means of creating the required oscilla- 
 tions, the Marjorana system employs an arc essentially identical with 
 that used by Poulsen. The transmitting arrangement, however, is 
 characterized by a peculiar manner of accomplishing the variations 
 of intensity of the radiated waves. The complete circuit, including 
 diagrammatic representation of the Marjorana liquid microphone, 
 or transmitter, is shown in Fig. 18. The aerial is inductively coupled 
 with the source of oscillations. The arc is fed through the blow-out 
 
 no 
 
WIRELESS TELEPHONY 
 
 23 
 
 magnets, which thus serve as choke coils to prevent the high-fre- 
 quency current from flowing through the direct-current dynamo, 
 which acts as supply. The receiving portion of the system possesses 
 no points of novelty, as it is of the simple inductively coupled type 
 and employs any of the well-known detectors suitable for this class 
 of work. 
 
 It is the transmitter which, as suggested above, forms the dis- 
 tinguishing feature of this system. Its action is based upon the fact 
 observed by Marjorana that a steady stream of water falling from 
 an elevated containing vessel through a small orifice may have its 
 uniformity modified by extremely minute mechanical jars imparted 
 
 \ABf64L 
 
 AEWAL 
 
 Fig. 18. Circuits of Marjorana System 
 
 to the containing vessel. The liquid transmitter is designed to take 
 advantage of this property, and is shown partially in section in the 
 illustration. A stationary rigid containing vessel V terminates at its 
 lower end in a small hole through which the water, constantly sup- 
 plied to said vessel, is allowed to flow continually in the form of a 
 minute stream. Interposed in the path of this stream is a small gap 
 in the aerial formed by two platinum points separated a short dis- 
 tance. The stream completes the connection across this gap. Means, 
 in the form of a thin diaphragm introduced as a portion of the 
 wall of the containing vessel, are provided to affect the diameter 
 and contour of the stream in accordance with the vibrations of the 
 voice. The center of this diaphragm is connected by a light rod 
 to the center of another diaphragm which is acted upon by the 
 
 ill 
 
f 
 
 24 WIRELESS TELEPHONY 
 
 voice through suitable mouthpiece. The action is as follows: The 
 vibrations of the double diaphragm are communicated to the volume 
 of the liquid in the form of variations of pressure manifested at the 
 orifice and resulting in similar variations in the volume of water 
 constituting the stream. Such modifications of the stream produce, 
 at its juncture with the platinum electrodes of the aerial, corre- 
 sponding variations in the resistance of the gap. It is of course 
 obvious that this action produces corresponding variations in the 
 intensity of the radiations. Numerous fluids and electrolytes have 
 been employed by Marjorana in place of water. A form of ionized 
 gas detector has been used in connection with this system with 
 excellent results. 
 
 Fessenden System. In reviewing the development of radio- 
 telephony it has been necessary to refer so often to the work of Fes- 
 senden relative to the many innovations introduced into the art by 
 him that little remains to be said in this place in regard to the com- 
 plete system which bears his name. The bibliography of radio- 
 telephony includes many papers and articles by Fessenden of the 
 greatest interest to the student of wireless communication. A re- 
 markably clear and concise paper on thp subject of wireless telephony, 
 replete with much valuable data on transmission, etc., was presented 
 by Prof. Fessenden at the 25th annual convention of the American 
 Institute of Electrical Engineers at Atlantic City in June, 1908. 
 Many illustrations and descriptions of the apparatus employed by 
 him were given. 
 
 Among the many interesting facts determined by Fessenden in 
 his very exhaustive tests dealing with the atmospheric absorption 
 of electric waves, may be mentioned the fact that waves of a com- 
 paratively low frequency suffer less absorption than those of a much 
 higher frequency, both being of equal power. Messages were suc- 
 cessfully transmitted in daylight with a wave-frequency of 80,000 
 per second from Brant Rock, Massachusetts, to a radiotelegraphic 
 station in the West Indies a distance of 1,700 miles with compara- 
 tively little absorption ; while at the higher frequency of 200,000 per 
 second communication was impossible. 
 
 The power required for radiotelephony, Fessenden states to be 
 about five to fifteen times that required for radiotelegraphy. Fes- 
 senden has employed at various times all the well-known methods 
 
 112 
 
WIRELESS TELEPHONY 
 
 25 
 
 of generating a sustained train of waves but has met with greater 
 success, particularly in radiotelephony, by the use of some form of 
 the high-frequency alternator method, shown in Figs. 6, 7, and 12, 
 used in connection with the heterodyne receiver illustrated in Fig. 13. 
 
 The Fessenden system has transmitted speech from Brant 
 Rock to New York City with an expenditure of about 200 watts. 
 Longer distances have also been covered with higher power apparatus. 
 Fessenden 's patents are controlled by the National Electric Signaling 
 Company. 
 
 DeForest System. This system is exploited by the Radio- 
 telephone Company and is due to Dr. Lee DeForest. It is an oscil- 
 
 AEff/AL 
 
 Pig. 19. Operating Circuits of the DeForest System 
 
 lating arc system presenting nothing of special novelty. Fig. 19 
 shows the essential features of the operating circuits, though in prac- 
 tice a more convenient means is provided for facilitating the change 
 from the transmitter to receiver. The arc is of the Poulsen type, 
 taking place between a copper positive electrode, water cooled, and 
 a carbon negative. An electromagnetic means is provided for 
 automatically adjusting the length of the arc by a movement of the 
 carbon through the agency of a solenoid, which is represented in the 
 drawing by the turns of wire around the left-hand electrode. A 
 variable resistance is employed to effect the proper regulation . of 
 this feature. The arc is made to burn in the flame of a small alcohol 
 lamp. The aerial is inductively coupled to the closed oscillation 
 circuit, the latter containing two condensers connected in multiple, 
 
 113 
 
26 
 
 WIRELESS TELEPHONY 
 
 one of which is adjustable for tuning purposes. A small incan- 
 descent lamp, connected to a closed circuit, is placed in inductive 
 relation with the primary of the oscillation transformer in order to 
 give a visual indication of the proper working of the oscillation arc. 
 The transformer used for inductive coupling with the aerial is of 
 compact flat spiral design, the primary and secondary being placed 
 side by side in a loose inductive couple. For telegraphic and "call- 
 ing" purposes, a device for rapidly interrupting the steady flow of 
 waves, called a "chopper," is thrown in by the movement of a switch; 
 whereupon it becomes possible, by the operation of the Morse key, 
 to cut up the wave-train into any desired combination of dots and 
 
 Fig. 20. Circuits of the Collins System 
 
 dashes. The telephone transmitter, which is introduced betweer 
 the aerial and the ground, is out of circuit during such a performance. 
 A hot-wire ammeter is placed in the aerial circuit to indicate when 
 the latter is in tune. For the detector, a form of the DeForest audion 
 receptor is used, connected in the circuit as shown. 
 
 The DeForest system has met with considerable success, and 
 has been installed on several United States battleships. Tests 
 have been made with the DeForest equipment by the British Ad- 
 miralty, and the greatest distance over which it was possible to 
 transmit satisfactorily was about 57 miles, a distance which has since 
 been extended with improved apparatus. The sound from phono- 
 graphic records transmitted by this system when temporarily in- 
 stalled at the Eiffel Tower in Paris, was said to be audible 400 miles 
 
 114 
 
WIRELESS TELEPHONY 27 
 
 away. This station permitted of the use of an exceedingly tall 
 aerial, the tower being nearly 1,000 feet high. 
 
 Collins System. This system has been developed by A. F. 
 Collins, who for several years has carried on experiments in the 
 field of radiotelephony. The circuits employed are shown in Fig. 
 20, the arrangement including some unusual features though nothing 
 in the nature of a radical 
 departure. The oscillations 
 are created by an arc of a 
 higher potential than is gen- 
 erally used, 5,000 volts be- 
 ing supplied through the 
 agency of a direct-current 
 dynamo directly coupled to 
 a 500-volt motor. The elec- 
 trodes of the arc are both 
 
 in the form of carbon disks, . pig 2l Oo , Uns Kevolving Blectrode8 
 
 which are made to revolve 
 
 by means of a small motor, as shown in Fig. 21. A magnetic blow- 
 out is also provided, the coils of which serve the purpose of choke- 
 coils, thus preventing the oscillatory current from entering the gener- 
 ator. The aerial is of the direct-coupled type in both the transmit- 
 ting and receiving stations. A visual indication of the correct working 
 of the arc takes place in the form of a glow within an exhausted glass 
 tube. This tube is supplied with platinum terminal wires sealed into 
 the ends, and projecting inwardly to within a short distance from each 
 other. This device is shunted across the inductance in the closed 
 oscillatory circuit. The transmitter is located in a local-battery 
 circuit and acts inductively on a shunt connected across the ter- 
 minals of the arc. This shunt includes the secondary of the induc- 
 tion coil and a condenser. Collins has recently employed several 
 transmitters connected in multiple and operable through a common 
 mouthpiece. The detector employed in this system is the invention 
 of Collins, and is in effect a sensitive thermo-electric couple com- 
 posed of two dissimilar metals, the juncture of which is heated by 
 the received oscillations. The variation of this thermal effect 
 produces a corresponding variation in the effective resistance 
 of the detector, and consequent vibrations of the receiver diaphragm, 
 
 115 
 
28 WIRELESS TELEPHONY 
 
 The Collins system is exploited by the Collins Wireless Telephone 
 Company of Newark, New Jersey. 
 
 Conclusion. In conclusion attention is called to an important 
 characteristic of radiotelephonic communication which has been 
 observed in practice, namely, the exceptional clearness of articula- 
 tion, due to an absence of wave-form distortion which is always 
 present in wire telephony by reason of the deleterious effect of the 
 electrostatic capacity of metallic lines and cables. This fact alone 
 bespeaks wonderful promise for this form of telephony, particularly 
 in view of the very limited distance over which it is at present possible 
 to telephone when the medium is a submarine cable. 
 
 Experience has thus far shown that great advantage is to be 
 gained by the very accurate tuning of the various circuits in connection 
 with radiotelephony as well as with radiotelegraphy. The employ- 
 ment of sustained oscillations greatly facilitates the accomplishment of 
 more perfect resonance; which, in turn, tends to eliminate interference 
 and aids selective communication. Experience has also shown that 
 in systems using an inductively coupled aerial, a decided gain in the 
 clearness of articulation is noticeable when such coupling is " loose." 
 In practice, therefore, the primary and secondary helices are often 
 separated several inches. 
 
 In the foregoing discussion of radiotelephony it has been impos- 
 sible to do more than very briefly present the subject. Many in- 
 teresting questions of a theoretical nature and a description of several 
 other systems, it has been found necessary to omit. If, however, the 
 present short survey awakens a greater interest in space-communica- 
 tion, the reader may avail himself of the extensive literature dealing 
 with the subject, and delve as deeply into the theory and problem* 
 involved as he desires. 
 
 116 
 
WIRELESS TELEGRAPHY IN 
 AERONAUTICS 
 
 WIRELESS ON DIRIGIBLES 
 
 Early Experiments on Balloons. It will be apparent that one of 
 the most valuable features of the use of the dirigible and the aero- 
 plane in warfare is the possibility of communicating with headquar- 
 ters by wireless telegraphy, which means the instant reception of 
 information gained by scouting parties. Not long after the inven- 
 tion of sending messages through the air became a reality, Professor 
 Slaby demonstrated that wireless signals emitted by a land station 
 can be received by a balloon, floating freely in the air. The experi- 
 ments were carried out in conjunction with the maneuvers of the 
 Prussian balloon corps, and since then experiments have been made 
 successfully in other countries. The balloon Condor, which made 
 an ascension near Brussels, in the latter part of 1909, maintained 
 uninterrupted communication with the station on the Brussels 
 Palais de Justice, and also caught signals sent from the Eiffel Tower 
 at Paris, 180 miles distant. Prior to this, Professor Hergesell had 
 already demonstrated the great value of the application of wireless 
 telegraphy to balloons by controlling the valves of unmanned sound- 
 ing balloons (small balloons sent aloft for the purpose of carrying 
 meteorological instruments), at heights extending to ten miles, by 
 wireless impulses. The receivers of the balloons were tuned to 
 different wave lengths, so that the valve of any one balloon could be 
 opened and that particular balloon brought down at will. 
 
 In a series of experiments made with the German military bal- 
 loon Gross II, in the autumn of 1908, messages were sucessfully 
 sent from, as well as to, the airship, the first balloon wireless stations 
 being constructed according to the Telefunken system. It was 
 proved by preliminary experiments in the balloon shed that the dan- 
 ger of igniting the contents of the gas bag by sparks emitted from the 
 wireless apparatus could be averted by taking suitable precautions. 
 
 119 
 
.2 WIRELESS TELEGRAPHY IN AERONAUTICS 
 
 This danger is least with airships of the flexible and semi-rigid types, 
 in which the gas bag possesses very few metallic parts that could 
 draw sparks from the highly charged aerial which is used for sending 
 and receiving the flashes from the air. The suspension of the car of 
 the Gross by hempen ropes insured the complete insulation of the 
 electrical apparatus from the gas bag, and all parts at which sparks 
 were formed were enclosed in gas-tight envelopes. For military 
 reasons, the details of these experiments were not made public, but 
 the results are said to have been very satisfactory. 
 
 These experiments have proved that electro-magnetic waves 
 are propagated to great heights in the atmosphere and that the part 
 played by the earth in wireless telegraphy is far less important than 
 has been assumed. Thus, one of the principal theoretical objections 
 to the application of wireless to airships has been shown to be falla- 
 cious. In the German army maneuvers of 1909, the Gross II demon- 
 strated, for the first time, the practical utility of wireless teleg- 
 raphy on a scouting balloon. The Zeppelin airship which took part 
 in the maneuvers did not possess this advantage. Subsequently 
 the Zeppelin III was equipped with wireless apparatus and it was 
 shown that even with a rigid, metallic-framed airship of this type, 
 wireless signals could be transmitted with safety to a distance of 300 
 miles or more. All of the later Zeppelin airships which have since 
 been wrecked, and particularly the passenger-carrying types, were 
 equipped with wireless. 
 
 Dangers from Electric Discharge. While of inestimable advan- 
 tage, the presence of the wireless apparatus on a metallic airship 
 exposes it to new dangers, some of which are also present in the case 
 of the aeroplane. The chief source of risk is the large volume of 
 inflammable gas necessary for flotation in the case of the huge diri- 
 gibles. In a thunder storm, a balloon is subject to sudden varia- 
 tions of electric charge which may produce sparks capable of ignit- 
 ing its contents. Wireless signals are accompanied by equally great 
 and rapid changes of potential which may produce the same result. 
 
 It seems probable that the destruction of the Zeppelin airship 
 at Echterdingen was due to atmospheric electric discharges during 
 a thunder storm, while the catastrophe which befell the French mili- 
 tary dirigible La Republique in September, 1909, also appears to 
 have been due indirectly to an electric spark. A hole was torn in 
 
 120 
 
WIRELESS TELEGRAPHY IN AERONAUTICS 3 
 
 the gas bag by the breaking of a propeller blade, which in itself would 
 not have been sufficient to have caused the sudden drop of 300 feet. 
 It is a well-known fact that gas or steam, escaping rapidly from an 
 orifice, will acquire an electric charge which may produce powerful 
 sparks, and it is thought that this took place immediately follow- 
 ing the rupture of the gas bag of the Republique, setting its contents 
 on fire. 
 
 As the gas can not be ignited by discharges from the envelope 
 itself, the netting, ropes, and similar poor conductors (unless they 
 become saturated with water), but can be easily set fire to by sparks 
 from the metal parts of the valve and other masses of metal, it is 
 obvious that all metal and other good conductors will have to be 
 eliminated from the envelope. There seems to be no objection to 
 the presence of metal in the car, while a well-conducting drag rope 
 is a safeguard against explosion in landing. If all conductors are 
 removed from the vicinity of the gas bag, there would appear to be 
 no danger in the application of wireless telegraphy to airships of the 
 flexible type. If the same precautions be taken, dirigibles of this 
 class are no more liable to ignition by atmospheric electrical dis- 
 charges than the free balloon. 
 
 In rigid airships with metallic frames, the conditions are totally 
 different. It will be apparent in the Zeppelin type, with its alumi- 
 num frame and its numerous gas bags filled with hydrogen, every 
 condition of easy ignition is present. Between the great cylindrical 
 conducting frame, which is more than 400 feet long and 40 feet in 
 diameter, and the surrounding air, there may exist a difference of 
 potential of 65,000 volts when the airship is horizontal, and of 50,000 
 volts, when steeply inclined. A spark capable of causing ignition 
 may be caused by a difference of potential of only 3,000 volts. As 
 it does not appear to be practicable to substitute wood for the alumi- 
 num framing, Zehnder recommends protection of airship by light- 
 ning rods projecting beyond the reach of escaping gas, He also 
 suggests making the gas container of sheet metal, the stiffness of 
 which might make it possible to employ a lighter skeleton, thus keep- 
 ing the weight within the same limit as at present. No electrical 
 discharge could take place within this metallic envelope and the 
 induced surface charge would escape harmlessly into the atmosphere 
 from projecting seams and points. As an additional precaution, 
 
 121 
 
4 WIRELESS TELEGRAPHY IN AERONAUTICS 
 
 the aluminum cars could be connected with the aluminum balloon 
 at several points by a number of wires, so that the aeronauts would 
 be enclosed in a sort of Faraday's cage, protecting them from exter- 
 nal electrical influences. 
 
 Preventive Methods. The experiments of Professor Wiener 
 have not only served to demonstrate the value of a wire cage as 
 protection against electrical discharges, but likewise have illustrated 
 what happened to a balloon when struck by a spark. For this pur- 
 pose, a model balloon was suspended above a large induction coil 
 with the gaps of the secondary so arranged that the largest diameter 
 of the balloon was between one pair, while a second pair was located 
 to discharge immediately below the valve opening of the balloon. 
 When a spark was passed completely through a collodion balloon, 
 filled with either hydrogen or illuminating gas, the gas ignited with- 
 out explosion so that the balloon was quietly consumed. It is only 
 when the balloon contains air mixed with gas that explosion takes 
 place. A balloon can even be traversed by sparks without being 
 ignited. Metzeler has recently introduced a balloon material com- 
 posed largely of aluminum for the purpose of protecting the gas from 
 the sun's rays, but experiments prove that this material is no better 
 conductor than the ordinary balloon fabric. Sparks can be passed 
 through a balloon of Metzeler's material without causing ignition 
 and even collodion balloons can transmit a few sparks without burn- 
 ing. If the flow of sparks be so rapid and dense as to resemble a 
 flaming arc, it may directly ignite the fabric. Even if it were pos- 
 sible to make a balloon of conducting material, it would still be 
 desirable to surround it with a wire cage, as lightning naturally fol- 
 lows the shortest path. With this provision, the conductivity of 
 the balloon is of no importance. Owing to its greater strength the 
 wire netting need not be heavier than the hemp netting ordinarily 
 employed on dirigibles of the flexible and semi-flexible types. All 
 the experiments just referred to were made with unprotected bal- 
 loons, but a model surrounded by a wire cage allowed ordinary sparks 
 to pass indefinitely, while it also withstood a flaming arc for a short 
 time, without igniting. Fifteen seconds direct contact with the 
 flame was necessary to produce ignition. The ropes supporting 
 the car must also be of wire and must, completely surround the car. 
 It might be supposed that making the outside of the balloon a good 
 
 122 
 
WIRELESS TELEGRAPHY IN AERONAUTICS 5 
 
 conductor would rather invite danger from lightning, but this is not 
 the case. Although the ordinary balloon envelope is a fairly good 
 insulator against low voltages, it is unable to resist the high tension 
 of atmospheric electricity. An electroscope charged to 2,000 volts 
 is discharged in less than a second, when it is touched with a roll 
 of balloon fabric about six inches long. Hence, the balloon increases 
 the electrical tension immediately above and below it, as much as 
 it would do if it were a perfect conductor, but when the discharge 
 occurs, its destructive action will be greater in proportion to the 
 electrical resistance opposed to it. It might also be objected that 
 the Faraday's cage would prove a source of danger to the occupants. 
 The discharge, however, passes chiefly through the wires, and only 
 partial or inductive discharges can strike those in the balloon. It 
 is evident that the Faraday's cage is quite as readily applicable to the 
 aeroplane as it is to the dirigible, through its use might complicate the 
 employment of the aerial for wireless telegraphy, as referred to later. 
 
 On the other hand, it is quite possible that the surrounding net- 
 work of wire might be employed for both purposes by suitably pro- 
 tecting the instruments. But even when a balloon is thus pro- 
 tected from lightning, it is exposed to another danger, atmospheric 
 electricity. A balloon has been ignited and consumed by small 
 sparks produced by touching the escape valve after landing. This 
 valve and the filling tube, normally open during flight, are the two 
 places in which the gas can come into contact with the air and there- 
 fore need special protection. The simple and long-known device 
 employed in the Davy safety miner's lamp can well be employed for 
 this purpose. These safety lamps are designed to protect miners 
 from explosions of fire damp, the flame being surrounded by a fine 
 wire netting which conducts heat so well that the temperature 
 required to ignite the gas can not be produced on the outside. Any 
 gas which enters the lamp burns quietly without producing an explo- 
 sion. Both the escape valve and filling tube of the balloon could be 
 surrounded with a fine netting of copper wire, which would also 
 afford protection from lightning in certain cases. 
 
 An electric discharge may be precipitated by pulling the valve 
 cord in a strong electric field, as, according to Paschen's experiments, 
 the gap that a certain tension will bridge is greater in hydrogen than 
 in air. This is shown by connecting a Bunsen burner with one 
 
 123 
 
6 WIRELESS TELEGRAPHY IN AERONAUTICS 
 
 pipe of an induction coil and gradually raising the other above it until 
 the opening is too great for the sparks to bridge. Upon turning on 
 the gas, the flow of sparks will recommence. If the burner be sur- 
 rounded with a wire netting, the gas will burn only on the outside. 
 The experiments with the model balloons and a large induction coil 
 showed that when the sparks passed beneath the open filling tube of 
 the balloon, ignition sometimes followed, but where protected by 
 a wire netting, a flaming arc playing upon the netting for a minute 
 did not light the gas. 
 
 Wireless on the Zeppelins. In regard to the employment of 
 wireless telegraphy on the Zeppelin type of the present form an 
 arrangement of the aerial which would minimize the danger of igni- 
 tion and would also furnish the best electrical conditions for the 
 transmission of signals, is suggested; as the hull of the Zeppelin is 
 traversed by a vertical shaft or well, it is possible to support the 
 aerial by a simple Eddy kite, which would be kept aloft by the motion 
 of the airship. The wireless apparatus, including the dynamo, would 
 be housed in the middle of the runway which connects the two cars. 
 The kite would be connected with the apparatus by a wire from 600 
 to 1,200 feet in length, i. e., one-fourth to one-fifth the length of the 
 electric waves employed. A second wire of the same length and 
 carrying a weight at its end would hang downward from the appara- 
 tus and would be kept as nearly vertical as possible by insulated 
 stay or guy lines attached to the cars. The lower wire might, 
 however, be replaced by a fan-shaped antenna about 200 feet long, 
 attached to the frame of the airship and projecting about 30 feet 
 below the hull. With this arrangement communication would be 
 possible even when the ship was flying low. Fouling of the propel- 
 lers would have to be guarded against by enclosing them in wire 
 baskets or housings. 
 
 The T-shaped antenna which is carried by ships using the Tele- 
 f unken system, could also be applied without difficulty to the Zeppe- 
 lin airship, as the metal frame is abundantly able to carry a light, 
 hollow mast about 30 feet high, which could be raised and lowered 
 by ropes. The stability of the airship, however, would be affected 
 more by this complicated device than by the kite. Experiments 
 have shown conclusively the great promise of the use of wireless teleg- 
 raphy on airships, but an indispensable prerequisite to its adoption 
 
 124 
 
WIRELESS TELEGRAPHY IN AERONAUTICS 7 
 
 would appear to be the electro-technical development of means of 
 protection from all danger of injury through the working of the appa- 
 ratus itself, or from atmospheric electricity. 
 
 WIRELESS ON AEROPLANES 
 
 Owing to its far greater speed and radius of action as well as its 
 more general availability, the employment of wireless telegraphy 
 on the aeroplane holds far more promise for military use. With 
 experience in taking observations from a height it will become pos- 
 sible to plot maps, note the character of emplacements, and the posi- 
 tion of troops from an altitude that would make danger from shell 
 fire from below out of the question. To be of any value, the diri- 
 gible must be so large as to make this impossible. 
 
 First Message. To James McCurdy, one of the Curtiss school 
 aviators, belongs the distinction of having been the first to communi- 
 cate by wireless from an aeroplane to a land station. This was on 
 August 27, 1910, when he sent the following message from a Curtiss 
 biplane : 
 
 Over Barren Island, N. Y., 6:45 P. M., Aug. 27, '10. 
 To H. M. HORTON: 
 
 Another chapter in aerial achievement is recorded in the sending of this 
 wireless message from an aeroplane in flight. McCuKDY. 
 
 Horton was the wireless operator on the roof of the Sheepshead 
 Bay race-track grand stand, two or three miles distant from Bar- 
 ren Island, though the distance was probably less in an airline. The 
 apparatus was an ingenious makeshift merely intended for the pur- 
 pose of sending and was not capable of receiving a message. It was 
 extremely compact, the complete outfit, with the exception of the 
 battery, being attached to the steering wheel of the aeroplane. The 
 battery was carried in the aviator's vest pocket, while the aerial 
 consisted of 50 feet of ordinary wire held straight by a small lead 
 weight, the whole trailing after the machine in flight. Such an out- 
 fit naturally had but a very limited range, probably not more than five 
 miles, owing to the small amount of energy available, and would be 
 subject to destructive interference from the waves sent out by more 
 powerful stations in its vicinity. It was intended only to demon- 
 strate the possibility of communicating with an aeroplane in flight. 
 
 125 
 
8 WIRELESS TELEGRAPHY IN AERONAUTICS 
 
 Owing to the high speed at which an aeronautic motor runs, how- 
 ever, it would be practical to carry a very compact alternating gener- 
 ator which would weigh very little and still give the aeroplane send- 
 ing station a comparatively wide radius of action doubtless up to 
 100 miles or more, due to the greater facility with which the electro- 
 magnetic waves can be transmitted from a height. The remainder 
 of the apparatus could likewise be made in very compact and durable 
 form, so that there would appear to be no "wireless problem" where 
 the aeroplane is concerned it is merely a matter of designing instru- 
 ments for the purpose. 
 
 Morton's Experiments. The question of equipping the aero- 
 plane with a suitable aerial that would be effective without being an 
 encumbrance, as well as the fact that a very substantial percentage 
 of the energy emitted by the sending apparatus was absorbed by 
 the numerous guy wires which also acted as a shield to the antennae, 
 appeared to present a difficult obstacle at first. Both, however, have 
 been overcome by a very simple expedient, that of employing the 
 guy wires themselves as the antennae. After experimenting for a 
 long while with numerous different methods of stringing separate 
 antennae, H. M. Horton hit upon the idea of using the wires for 
 this purpose, while the motor is utilized as a ground. Experiments 
 which were made with a machine thus equipped and located in the 
 building of the United States Aeronautical Reserve in New York 
 City, proved most successful. Messages were received from vari- 
 ous stations throughout the city and even from ships at sea, despite 
 the fact that the aeroplane was located on the first floor of the build- 
 ing and was not connected with any form of antennae protruding 
 above the roof. A very light equipment was used, the total weight 
 not exceeding 65 pounds, although a 6-inch spark coil was employed. 
 Energy is derived from a 12-volt storage battery with a 50-ampere- 
 hour capacity, the six cells weighing but 40 pounds. The guy wires 
 are connected in series and give a total length of 800 feet on the 
 machine in question. However, the employment of a storage bat- 
 tery in this connection can be considered only as a tempory expe- 
 dient, in view of the obvious limitations of such a source of energy. 
 For extended practical use, a generator would be necessary. As 
 the required power is right at hand, this could take the form of 
 a small high-frequency alternator, and as this could be wound for a 
 
 126 
 
WIRELESS TELEGRAPHY IN AERONAUTICS 
 
 9 
 
 high voltage, the weight of the transformer necessary could be cor- 
 respondingly reduced. 
 
 Recent Records. Lorraine. Numerous other experimenters 
 have been at work with wireless during the past year or so, Robert 
 Lorraine, in England, having succeeded in maintaining perfect 
 communication from his aeroplane with a land station more than 
 a mile distant. 
 
 Beck. The most practical results, however, were those of the 
 trials carried out during the course of the aviation meet at San 
 
 Fig. 1. Parmalee and Lieutenant Beck in a Wright Biplane, Operating 
 a Wireless Outfit 
 
 Francisco in January, 1911. Lieutenant Paul W. Beck of the United 
 States Signal Corps went aloft in a Wright biplane piloted by Parm- 
 alee, Fig. 1, and transmitted wireless messages for a considerable 
 distance while at a height of 1,000 feet. These messages were 
 received at the Mare Island Navy Yard, 40 miles away, as well as 
 at the Yerba Buena Island training school in San Francisco Bay. 
 In Lieutenant Beck's experiments a 100-foot length of copper wire 
 was trailed along behind the aeroplane. In France, wireless mes- 
 sages have been transmitted 15 miles from an aeroplane success- 
 fully, while in England, during a trip of the military dirigible 
 
 127 
 
J 
 
 10 WIRELESS TELEGRAPHY IN AERONAUTICS 
 
 Beta, communication was established with headquarters, 30 miles 
 distant. 
 
 McCurdy. During the Bridgeport, Connecticut, Aviation Meet 
 in May, 1911, McCurdy set a new long-distance mark in wireless 
 communication from an aeroplane by sending messages to the opera- 
 tor in the dome of the World Building in New York City, 55 miles 
 distant, while a number of other stations within a shorter radius 
 also picked up his messages. The apparatus was constructed for 
 the New York World in three days by Oscar Roesen, an electrical 
 engineering student at Stevens, and was probably the first set capable 
 of both sending and receiving that has been mounted on an aero- 
 plane. The transmitter consisted of a 4-inch induction coil of the 
 
 Fig. 2. Diagram Showing Method of Making an Aerial on a Biplane 
 
 ordinary vibrating type, supplied with current by 15 dry cells con- 
 nec^ed in series, thus giving a voltage of 22.5, while the amperage 
 was high. The helix was a wood frame 5 inches in diameter and 
 wound with 12 turns of No. 6 B & S gauge aluminum wire, while the 
 condenser consisted of copper plates with a special insulating material 
 as the dielectric. An ordinary telegraph key was employed. The 
 receiver comprised a mineral detector, two straight tuning coils, and 
 a pair of 2,000-ohm head phones. The aerial consisted of a series 
 of wire strung forward from the tail on either side to points directly 
 above the ailerons at the ends of the upper plane of the Curtiss 
 machine, Fig. 2. For a ground, or rather for a balancing aerial, 
 
 128 
 
WIRELESS TELEGRAPHY IN AERONAUTICS 11 
 
 the motor, supplemented by wires carried out in either direction 
 to the ends of the main plane, was employed. The apparatus 
 proper was mounted in a small box carried below the aviator on the 
 skids of the machine, while the sending key was placed on the steer- 
 ing wheel. The arrangement is plainly illustrated by the accompany- 
 ing sketch, Fig 3. A is the box, B the key, dotted lines C the 
 ground or balancing aerial, and full lines CC the aerial proper. The 
 weight of the outfit was between 40 and 50 pounds. Lieutenant 
 Fickel, U. S. A., detailed by the War Department to attend the 
 meet, was very much impressed with the set and sent a complete 
 description of it to the Signal Corps at Washington. Experiments 
 were first made on a y Saturday, and while McCurdy's signals were 
 
 Fig. 3. Diagram Showing Location of Circuits and Equipment of a 
 Wireless Outfit 
 
 plainly heard at the temporary receiving station on the field, the 
 interference of numerous adjacent stations made it impossible for 
 the operator in New York to pick them up. On the following day, 
 there was an absence of interference, and the messages were plainly 
 heard in New York on three different trials, thus establishing a new 
 distant record for aeroplane work, and this is of even greater impor- 
 tance in having reached the heart of the metropolis, as New York 
 City is generally conceded to have many adverse elements for suc- 
 cessful wireless .reception from outside points, chiefly due to the 
 great number of high, steel-frame buildings. Tests which were 
 made of the receiving abilities of the set showed that it was abund- 
 antly capable of picking up messages from a distance of 200 miles, 
 but, unfortunately, no actual trials of this nature were carried out 
 in the air. 
 
 129 
 
12 WIRELESS TELEGRAPHY IN AERONAUTICS 
 
 General Problems. It will be apparent from the foregoing 
 that all of the experiments made thus far have been in transmitting 
 messages from an aeroplane in flight, and while this is a very val- 
 uable accomplishment, receiving is quite as necessary, to take com- 
 plete advantage of the value of the wireless as a means of communica- 
 tion, and for reasons that are obvious this does present more of a 
 problem than the mere sending of messages. 
 
 Eliminating Noise. The chief difficulty is that of noise, as 
 with the unmuffled motors now generally in use, it is practically 
 impossible for two men sitting side by side in an aeroplane to carry 
 on a conversation. This is further complicated by the rush of the 
 wind and the high pitched note occasioned by the vibration of the 
 numerous guy wires and struts, but with close-fitting, double-head 
 receivers, there should be no difficulty in shutting out practically 
 everything but the noise of the motor. The matter of expediency 
 that has been responsible for the adoption of so many of the make- 
 shift features of design that characterize the present-day aeroplane, 
 and probably will continue to do, at least for a few years to come, 
 has likewise been responsible for the elimination of the muffler on 
 the motor. But even now, design and construction have advanced 
 to a point where there is really no necessity for longer doing without 
 this essential, as both the muffler and its connecting pipe can readily 
 be made of aluminum, though, for that matter, the weight of the 
 standard type as employed on the automobile would not form any 
 very serious drawback. Considerably more difficulty would be 
 encountered in muffling motors of the rotary type, but they need 
 it least, as the explosions of a seven- or fourteen-cylinder Gnome 
 motor running at full speed overlap to a degree that converts the 
 exhaust into a loud buzz, rather than the disagreeable and ear- 
 cracking rapid-fire bang of the four- or six-cylinder vertical motor. 
 
 Use of Visible Signals. Should the usual audible method of 
 receiving not prove practical, two alternatives are open, both involv- 
 ing the use of a visible signal. In one, a coherer could be connected 
 with a tuning condenser shunted across it, the former being auto- 
 matically decohered every two seconds by a striker actuated by a 
 magnet excited by a clockwork contact maker. A relay and bat- 
 tery are connected in series with the coherer, and the local circuit 
 of the relay is connected with another battery and small incandes- 
 
 130 
 
WIRELESS TELEGRAPHY IN AERONAUTICS 13 
 
 cent lamp. Each time a signal is received the lamp would light- 
 one second for a dot and two seconds for a dash. These long signals 
 are obviously necessary, but in spite of that a message could be 
 received with reasonable rapidity. The second alternative is that 
 of employing an inker, this method also involving the use of a coherer. 
 The inking apparatus, however, is not only comparatively heavy, 
 but in order to work satisfactorily, requires fairly close adjustment, 
 so that it would not be suitable for use where there is much vibration. 
 The question of vibration is probably the most serious element of 
 the problem. The coherer is not a particularly sensitive receiver of 
 the weak impulses which have to be caught, and has long since been 
 practically abandoned in wireless practice. But even if it were suf- 
 ficiently sensitive for such use, it would probably be impossible to 
 make the coherer work long enough to start the local side of the 
 relay working effectively, particularly if the mechanical decohe- 
 sion had to be rapid. In fact, the actual number of impulses per 
 second of a four-cylinder, two-cycle engine, or a six-cylinder, four- 
 cycle, or any of the rotary motors, is too great to permit a coherer 
 to act, while a coherer insensitive to the abruptness of the shock 
 would not be sensitive enough to respond to the wireless impulses. 
 Either the mineral or the electrolytic type of detector is far more 
 sensitive, but as its adjustment must be delicate to work effectively, 
 it would also be placed at a serious disadvantage by the vibration. 
 
 Forms of Aerial. The question of the most practical form of 
 aerial to employ is another difficulty that affects both sending and 
 receiving. The use of a long trailing wire, as well as the employ- 
 ment of the network of guys and braces, has already been referred 
 to in connection with experiments carried out by McCurdy and 
 American army officers. Trailing wires present so many sources of 
 danger to a machine traveling at high speed, that few pilots would 
 care to consent to their use, while connecting up the bracing of the 
 aeroplane is equally impracticable as every piece of metal on the 
 machine then becomes charged, and in sending, serious shocks might 
 be received by the pilot or his passenger. Farman has employed 
 two trailing wires, each about 400 feet long, and Baker has adapted 
 a similar arrangement to a Bristol biplane in England, the wires, 
 however, not being allowed to hang loose in the latter case, thus lim- 
 iting their capacity. Instead of using balanced aerials, as in the 
 
 131 
 
14 WIRELESS TELEGRAPHY IN AERONAUTICS 
 
 McCurdy experiments described above, he coupled them to each end 
 of an inductance coil, thus increasing their effective length to the 
 greatest extent possible without sacrificing their efficiency. The 
 apparatus consisted of a 6-inch induction coil with a %-inch spark 
 gap located as far away from the gasoline tank as possible. Two 
 light brass rods extended from the coil well into the space between 
 the two main planes of the machine and to one side of the tank, and 
 two ^-inch rods sliding on these and with their ends separated by 
 % inch, formed the spark gap terminals. Shunted across the spark 
 gap was a condenser of the Ley den jar type, and an inductance coil 
 consisting of seven turns of No. 14 copper wire wound on a light 
 ebonite drum. This inductance had sliding contacts so that the 
 number of turns used could be varied in the usual manner, in order 
 to tune the two circuits. The two aerial wires were connected to the 
 two ends of the inductance in use and the aerial circuit was brought 
 into tune with the shunt circuit. A storage battery of five cells 
 supplied the necessary energy, about 50 to 60 watts being required. 
 Two new arrangements which should greatly increase the efficiency 
 of the apparatus have since been adopted. The more important of 
 these is a long, light brass tube attached to the tail of the aeroplane 
 but insulated from it. This acts as counter-capacity or "ground" 
 to a long aerial wire on the other side. This aerial starts from the 
 nose of the machine, and is carried thence to the extreme outer edge 
 of the main plane, back to the tail, and from this to a loose connec- 
 tion, 60 feet of copper wire trailing behind. 
 
 Possible Developments. It is evident that these isolated experi- 
 ments, while more or less numerous, are but the beginning of the 
 serious study that will be given the matter within the next year or 
 so. Nine-hour, non-stop flights covering more than 400 miles give 
 some idea of what will be accomplished in the way of long-distance 
 flying in the near future in fact, they make the possibility of being 
 able to cover more than 1,000 miles per day of twenty-four hours 
 seem very close at hand, so that Atwood's proposal to fly across the 
 Atlantic in three days appears to be only a question of carrying suf- 
 ficient fuel. To be able to keep in constant communication with 
 these long-distance flyers would be invaluable, and that is what 
 experimenters in the wireless field aim to accomplish. 
 
 Wireless telegraphy from the dirigible has already reached a 
 
 132 
 
WIRELESS TELEGRAPHY IN AERONAUTICS 15 
 
 more advanced stage, as neither the use of a trailing wire nor the 
 matter of weight present such serious disadvantages as on the aero- 
 plane. The apparatus used on the British military dirigible Beta 
 weighed approximately 100 pounds, and as signals have been sent 
 50 miles under favorable conditions, the proportions of weight to 
 distance of transmission was, roughly speaking, 2 pounds. But an 
 ordinary induction coil and accumulator were employed, so that 
 this can scarcely be taken as a criterion. They were used in con- 
 nection with a trailing aerial and a counter-capacity, and, as the 
 chief requirement of the latter is superficial area to take the charge, 
 as light a substance as possible, such as paper-thin sheet aluminum, 
 could be employed. 
 
 The form of the wireless installation suggested by one of the 
 chief English experimenters as best adapted to the needs of the air- 
 ship, is that of a small auxiliary motor, say, a two-cylinder, 3- to 4- 
 horse-power machine, directly coupled to an alternating generator 
 of about 2 kilowatts capacity, together with an aerial about 350 feet 
 long, and a counter-capacity in the form of very thin metallic sheet- 
 ing, suitably disposed. Considerable attention is now being given 
 to the production of portable apparatus. The chief limiting factor 
 in connection with small receivers naturally has to do with the 
 detector, the vacuum valve type of Prof. J. A. Fleming probably 
 being the most suitable in many respects, and next to that an elec- 
 trolytic detector. 
 
 Akron Outfit. The ill-fated dirigible Akron, in which Melvin 
 Vaniman had intended making his second attempt at crossing the 
 Atlantic, when he and his gallant crew were killed by the fall 
 of the airship due to the explosion of the gas bag, is a forcible 
 example of the careful attention now being given to wireless equip- 
 ment and the dependence placed upon it as a safeguard. Vaniman 
 was particularly fitted by experience to judge of the wireless 
 requirements for a dirigible, as, it will be recalled, he was Wellman's 
 chief engineer on the America, and he had taken advantage of that 
 experience to embody all the improvements in the new equipment 
 that were found lacking in the America's set. The latter had a 
 sending range of only 80 to 90 miles, so that while the operator 
 could catch the numerous inquiries that filled the air regarding the 
 America's whereabouts during the 48 hours or more that it was out of 
 
 133 
 
16 WIRELESS TELEGRAPHY IN AERONAUTICS 
 
 sending range, he could not reply to any of them. The equipment 
 of the Akron was a Marconi set with a sending range of 700 to 800 
 miles and consisted of a 3-kilowatt, 120-cycle, alternating-current 
 generator, direct driven by a 17-horse-power, 4-cylinder gasoline 
 engine. For receiving, the most advanced type of musical, rotary 
 spark gap and a valve detector was to be employed. As a counter- 
 capacity does not permit of the most efficient operation, a flexible, 
 phosphor bronze wire trailing in the water was to constitute the 
 ground, the equilibrator which was used for that purpose on the 
 America having been abandoned. This trailing ground was wound 
 on a drum and sufficient wire was provided to reach the water at any 
 point from 100 to 1,200 feet elevation, the amount payed out 
 depending upon the height at which the airship was flying. How- 
 ever, should the airship rise higher, provision had been made to 
 operate the equipment as an unbalanced Hertz oscillator without a 
 ground. The transmitter was of the loose-coupled type and was so 
 arranged that considerable variation in the natural period of the 
 open oscillating circuit would have a minimum effect upon the 
 transmitted signals. The frame of the envelope was used as one side 
 of the oscillator, the trailing ground acting as the other. Particular 
 care had been taken in the design o! the various parts of the appa- 
 ratus to prevent any possibility of the sparking, or high-tension 
 discharge, igniting the hydrogen gas. Jack Irwin, whose call of 
 distress from the America brought the S.S. Trent to their rescue, 
 was to have accompanied the Akron as operator. 
 
 134 
 
INDEX 
 
 The page numbers of this volume will be found at the bottom of the 
 pages; the numbers at the top refer only to the section. 
 
 A Page 
 
 Aerials 55 
 
 Alternating-current transformers 46 
 
 B 
 
 Bell's photophone 91 
 
 Bell's radiophone 89 
 
 Branly coherer 24 
 
 C 
 
 Clark system of radiotelegraphy 80 
 
 Coherers 58 
 
 Branly 58 
 
 Italian navy 59 
 
 Lodge-Muirhead 58 
 
 tantalum-mercury 59 
 
 Collins system of radiotelephony - 115 
 
 Condensers 47 
 
 D 
 
 DeForest system 
 
 of radiotelegraphy 79 
 
 of radiotelephony 113 
 
 Detectors 57 
 
 audion 62 
 
 electrodynamic 65 
 
 electrolytic 65 
 
 Fessenden liquid barreter 65 
 
 glow-lamp 61 
 
 Hbzier-Brown 65 
 
 magnetic 62 
 
 thermo-electric 64 
 
 valve, or rectifier 56 
 
 E 
 
 Electric oscillations 12 
 
 Electric waves : 8 
 
 Note. For page numbers sec foot of pages. 
 
 137 
 
2 INDEX 
 
 Electric waves Page 
 
 electric oscillations 12 
 
 electromagnetic theory of light 8 
 
 nature of 11 
 
 resonance 17 
 
 wave-lengths 21 
 
 work of Hertz 14 
 
 Electromagnetic medium 9 
 
 Electromagnetic theory of light 8 
 
 electromagnetic medium 9 
 
 luminiferous ether. . 9 
 
 F 
 
 Faraday, work of 10 
 
 Fessenden system 
 
 of radiotelegraphy 72 
 
 of radiotelephony 112 
 
 H 
 
 Hertz, work of 14 
 
 energy of an oscillator 16 
 
 resonator 17 
 
 High-frequency alternators 52 
 
 Hughes, work of 27 
 
 I C' 
 
 Induction coils 41 
 
 interrupters 42 
 
 keys 45 
 
 primary condenser 42 
 
 L 
 
 Lodge, work of 27 
 
 Lodge-Muirhead system of radiotelegraphy 77 
 
 Luminiferous ether 9 
 
 M 
 
 Marconi, work of 27 
 
 capacity areas 31 
 
 development of the antennae , 31 
 
 early apparatus 28 
 
 inductive receiving antennae 32 
 
 inductive transmitting antennae 34 
 
 Note. For page numbers see foot of pages. 
 
 138 
 
INDEX 3 
 
 Marconi system Page 
 
 of radiotelegraphy 69 
 
 of radiotelephony 110 
 
 Massie system of radiotelegraphy 83 
 
 Maxwell, work of 10 
 
 O 
 
 Oscillation transformers 47 
 
 P 
 
 Poulsen system 
 
 of radiotelegraphy 83 
 
 of radiotelephony 109 
 
 R 
 
 Radiotelegraphic apparatus 40 
 
 aerials 55 
 
 alternating-current transformers 46 
 
 auxiliary apparatus 66 
 
 charging devices 40 
 
 condensers 47 
 
 detectors 57 
 
 directive antennae 57 
 
 high-frequency alternators 52 
 
 induction coils 41 
 
 measuring instruments 67 
 
 oscillation transformers 47 
 
 singing arc 53 
 
 sources of energy 40 
 
 spark gaps 49 
 
 tuning coils 49 
 
 Radiotelegraphy 
 
 development of 23 
 
 propagation of waves from grounded oscillator 36 
 
 selective signaling 38 
 
 systems of 68 
 
 Clark i 80 
 
 DeForest 79 
 
 Fessenden 72 
 
 Lodge-Muirhead , 77 
 
 Marconi 69 
 
 Massie 83 
 
 miscellaneous 83 
 
 Poulsen 83 
 
 Stone 82 
 
 Telefunken 74 
 
 Von Lepel , 76 
 
 Note. For page numbers see foot of pages. 
 
 139 
 
4 INDEX 
 
 Page 
 
 Radiotelephony, systems of 105 
 
 Collins ; 115 
 
 De Forest 113 
 
 Fessenden 112 
 
 Marjorana 110 
 
 Poulsen 109 
 
 Ruhmer 108 
 
 Telefunken 106 
 
 Resonance 17 
 
 Righi oscillator 24 
 
 Ruhmer system of radiotelephony 108 
 
 Singing arc . 53 
 
 Spark gaps 49 
 
 Stone system of radiotelegraphy 82 
 
 T 
 
 Telefunken system 
 
 of radiotelegraphy '. 74 
 
 of radiotelephony 106 
 
 Telegraphic codes 69 
 
 Transformers 
 
 alternating-current , 46 
 
 oscillation 47 
 
 Tuning coils 49 
 
 Von Lepel system of radiotelegraphy 76 
 
 W 
 
 Wave-lengths 21 
 
 Wireless telegraphy 1-86 
 
 on aeroplanes 
 
 first message 125 
 
 general problems '. 130 
 
 Horton's experiments 126 
 
 recent records 127 
 
 on dirigibles 
 
 early experiments on balloons 119 
 
 dangers from electric discharge 120 
 
 preventive methods 122 
 
 wireless on the Zeppelins 124 
 
 early forms 2 
 
 conduction systems ; 2 
 
 Morse system 2 
 
 Note. For page numbers see foot of pages. 
 
 140 
 
INDEX 5 
 
 work of Steinhall 2 
 
 induction systems 4 
 
 Dolbear system 4 
 
 Edison system 5 
 
 work of Preece 6 
 
 electric waves 8 
 
 radiotelegraphy 
 
 apparatus 40 
 
 development of 23 
 
 systems of 68 
 
 Wireless telephony Page 
 
 Bell's photophone 91 
 
 Bell's radiophone 89 
 
 "light telephony" 91 
 
 by means of Hertzian waves 92 
 
 nature of a high-frequency telephone current 94 
 
 oscillation generators 96 
 
 receiving arrangements 102 
 
 selenium cell 90 
 
 systems of radio-telephony 105 
 
 telephonic control of oscillations 97 
 
 transmitting circuits 98 
 
 two-way transmission .....,., i . t ...... 104 
 
 Note. For page numbers see foot of pages. 
 
 141 
 

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