LIBRARY OF THE UNIVERSITY OF CALIFORNIA. Class THE TELEGRAPHIC TRANSMISSION OF PHOTOGRAPHS THE TELEGRAPHIC TRANSMISSION OE PHOTOGRAPHS T. THORN E BAKER, F.C.S., F.R.P.S., A.I.E.E. NEW YORK D. VAN NOSTRAND CO. 23 MURRAY AND 27 WARREN 'STREETS 1910 PREFACE VERY little is known at present about the telegraphy of pictures, because -the published descriptions of the * instruments in use have been confined almost entirely to technical journals. The desire to have news at the earliest possible moment, and the recent demand by the public to have the " news in pictures," has opened up the field for a new science, which is a peculiar mixture of electricity, optics and photo- engraving. The telegraphed picture, at first looked upon as a marvel, now occasions little or no surprise, which means that it is sufficiently like an ordinary photograph to pass muster among the other pictures in the newspaper in which it appears. During the last two-and-a-half yeajrs, a great deal of experimental work has been carried out by me for The Daily Mirror, and it has been very largely owing to the active interest this journal has shown in photo-telegraphy that the pioneer work in this country has been possible. The interest displayed in the work by the editor, Mr. Alex. Kenealy, has never failed, and to his encouragement and enter- prise the present position of this new branch of telegraphic work is largely due. 210719 vi PREFACE The descriptions given in the book of the systems in use to-day will, I hope, make quite clear to the reader " how it is done." Though certain portions of the matter are intended for those already con- versant with the general principles of electricity, the bulk of the book has been written as simply as possible, and if the said portions are just passed over by the non-technical reader, I think the rest will be of interest to him. At the time of going to press, preparations are being made for an endeavour to transmit photographs by wireless telegraphy across the Wash, the Post- master-General having courteously allowed me the use of the experimental wireless stations at Hun- stanton and Skegness. The last chapter, therefore, dealing with wireless work, will make the reader acquainted with the latest phase of photo-telegraphic work. T. THORNE BAKER 15, GROSVENOR GARDENS, CRICKLEWOOD, N.W., March, 1910. CONTENTS PAGE PREFACE . . . . . . . . . . v LIST OF ILLUSTRATIONS . . ix CHAPTER I. Attempts at the Solution of the Telegraphic Transmission of Photographs and Pictures p. i CHAPTER II. Professor Korn's Selenium Process Early Work with his Original Receiver The String Galvanometer Syn- chronism First Experiments The Early History of Commercial Photo-Telegraphy . . . . p. 2,2, CHAPTER III. The Korn Telautograph Principles of Working Advantages over Selenium Early Work with Line Pictures Experi- ments with Telephone and Telegraph Cables Recent Progress with the Telautograph . . . . p. 61 CHAPTER IV. The Thorne- Baker System Differences between the Telectro- graph and Earlier Chemical Systems Electrolytic Records of Currents Transmitted through Long Cables The Thome-Baker Line-balance Work with the Electro- lytic Telectrograph p. 88 viii CONTENTS CHAPTER V. Considerations of the Telephone and Telegraph Lines and their Influence on Photo-Telegraphy . . . p. 108 CHAPTER VI. The Telestereograph of M. Belin The Early Work of Belin Changes in his System Recent Experiments . p. 116 CHAPTER VII. The Transmission of Photographs and Pictures by Wireless Telegraphy p. 127 INDEX 143 LIST OF ILLUSTRATIONS FULL PAGE ILLUSTRATIONS. A part of the Daily Mirror Installation, showing the Korn Telautograph and the Thorne- Baker Telec- trograph ....... Frontispiece Receiving a photograph on the Telectrograph . Opposite p. 100 ILLUSTRATIONS IN TEXT. FIG. PAGE 1. Diagram of Bakewell's instrument .... 3 2. Section of a film, showing silver deposit ... 13 3. Bernochi's wireless apparatus ..... 15 4. Polarisation receiver of Rignoux and Fournier . . 17 5. Diagram of selenium cell 22 6. Photograph of selenium cell 23 7. Diagram of Korn's selenium transmitter ... 24 8. Inertia curve of selenium 27 9. Curve showing effect of light on selenium ... 28 10. Korn's compensating bridge 29 11. Curve showing compensation of inertia ... 30 12. Curve showing compensation of inertia ... 30 13. Curve showing over-compensation . . . 31 14. Section of Korn's galvanometer . -33 15. Section of interior of galvanometer . . -34 1 6. Korn's receiving apparatus . . . . -37 17. Photograph of a galvanometer as used by Prof. Korn 38 1 8. Diagram showing synchronising arrangement . . 39 19. Diagram of friction clutch ... 41 20. Photograph of the frequency meter . -43 21. Diagram of switchboard connections . . 44 22. Prof. Korn at the telephone, when awaiting the first picture from Paris in 1907 . . 4 6 LIST OF ILLUSTRATIONS 23. Curve of selenium cell . 47 24. One of the first photographs wired by Korn's com- pensated selenium machines ... -49 25. Photograph of King Edward, wired to London November yth, 1907 . . 50 26. Photograph showing induction effects . . 53 27. Example of a news photograph sent from Paris . 55 28. Diagram illustrating principle of the telautograph . 62 29. Korn's telautograph transmitter . . 63 30. Diagram of stylus holder 65 31. Diagram of Korn telautograph ... -67 32. Diagram of synchronising arrangement ... 70 33. Wiring of reverser 71 34. Reception to Sven Hedin, wired from Paris to London by Telautograph 75 35. Example of Fashion Plate wired by the Korn Telautograph 77 36. Diagram showing duplex transmission . . -79 37. Line drawing transmitted by Telautograph . . 81 38. Example of line sketch from photograph, wired by the Korn Telautograph from Paris to London . 83 39. Damping of oscillograph string 85 40. Example of half-tone photograph transmitted from Berlin to Paris by Telautograph .... 86 41. Telectrograph tracing stylus 91 42. Curve showing charge and discharge of a cable . 92 43. Diagram of connections of line balancer ... 93 44. Photograph showing the balancing effect of the Telectrograph arrangement 94 45. Portrait of first lady councillor of Liverpool. Wired by the Telectrograph from Manchester to London 98 46. Portrait of Mr. Howarth, telegraphed from Man- chester to London by the Thorne- Baker Telectro- graph . ioo 47. Half-tone single line negative image, as ordinarily used for the Telectrograph . . . . .102 48. Finish of the St. Leger, wired by the Telectrograph . 104 LIST OF ILLUSTRATIONS xi 49. M. Riolle, Public Prosecutor in the Steinheil case ; wired from Paris to London by the Thorne- Baker Telectrograph . . 106 50. News photograph wired from Manchester to London of a railway accident at Staly bridge . . .107 51. Apparatus used to record oscillograph work . . 109 52. Oscillograph record of half-tone image with no capacity on line . ... no 53. The same with capacity, showing the elongation and widening of the " teeth " . . . . no 54. Section of a relief photographic film . . . .117 55. Diagram of Belin's transmitter . . . . .118 56. Photograph transmitted by M. Belin's Telestereo- graph, over an artificial line ..... 124 57. Belin's apparatus for telegraphing line pictures . 125 58. Diagram of wireless apparatus 130 59. Diagram of Marconi's Electromagnetic Detector . 132 60. Arrangement first used by the Author for the wireless transmission of pictures . . . . . 133 61. Sketch of head and shoulders of a lady. Trans- mitted by wireless 135 62. Diagram of the author's decoherer .... 136 63. Quartz string and selenium cell arranged for re- ceiving and transforming up electrical oscillations . 138 64. Sketch of the King transmitted by the author's wireless apparatus ....... 139 THE TELEGRAPHIC TRANSMISSION OF PHOTOGRAPHS CHAPTER I. ATTEMPTS AT THE SOLUTION OF THE TELE- GRAPHIC TRANSMISSION OF PHOTOGRAPHS AND PICTURES. THE problem of transmitting a sketch or photo- graph over a distance by means of electricity has occupied the minds of many engineers and scientists for the past sixty years, but it has been up to the present time a singularly ungrateful task, owing to the lack of possible application. The tendency for modern journals to be illustrated with photographs has very greatly widened the scope for an instru- ment by which they can be " wired/' and it is pro- bably for this reason that so much attention has of late been devoted to this new science. It seems difficult on first thought to conceive how a picture can be telegraphed. But a picture, just like a written message, can be split up into com- ponent parts ; the letters forming a 'word have a distinct meaning when seen assembled together in P.T. B 2 PHOTO-TELEGRAPHY proper order, while the dots and dashes forming a letter, according to the Morse code, possess simi- larly an intelligent meaning when grouped together in correct order ; by building up a complete picture with dots or small areas of varying depth, size, or density we can produce a picture in a strictly comparable manner. One ingenious attempt at the solution of photo -telegraphy as ingenious as it is impracticable has been to divide up a picture into thousands of small parts, representing each by a certain letter of the alphabet, according to its den- sity ; thus a light part might be called C or D, a dark part Y or Z, and so on. The letters are tele- graphed to an operator, who forms a fresh picture by building it up with small " parts/' whose densities are in accordance with the respective letters. Such a system is indeed possible, but would require a very great amount of time. It is the minutes and seconds which have to be saved in telegraphing a picture especially in these days of rapid railway transit, where photographic plates can be sent to the newspaper office in a few hours, so that only very late events are telegraphed. This book is not intended to be historical, and I shall therefore refer only to such early processes as have a direct bearing upon the work that is being done to-day. Of early attempts at the transmission of pictures, the Bakewell system deserves particular notice, since upon it is based one of the three BAKEWELL'S PROCESS 3 most successful modern methods of transmission. Bakewell's machine, which created some attention as far back as 1847, consisted of two synchronously revolving metal cylinders one at each end of the telegraph lines, over each of which a metal style traced a spiral path (in the manner of the modern phonograph). Upon one cylinder was placed a sheet of tinfoil with the sketch drawn in ink made with shellac, and on the receiving drum was placed a sheet of paper prepared chemically, so that on Battery FIG. i. passing an electric current through it a chemical mark or stain was made. It appeared as seen in Fig. i in its simplest form. A and B represent the two cylinders, tracing over which are shown two styles. A battery is in the circuit. It will be readily seen that when a line in the sketch which consists of shellac, comes under the style of A, the current flowing through the circuit will be broken, whereas when the bare tinfoil lies between style and cylinder the current will flow. This current therefore flows intermittently through the chemically -prepared paper attached to the drum /?, and when it flows, it causes a chemical 4 PHOTO-TELEGRAPHY mark on the paper. Hence, when the style has traced over the entire length of the sketch at A, the latter will be reproduced (negatively) at B. By suitable means it can, of course, be received posi- tively if desired. Such is the system which is now over sixty years old, and many trials were made with it to telegraph writing over distances ; here, however, the diffi- culties met with in long cables were at once felt ; attempts were actually made at one time in France to use such a system commercially, but they were soon abandoned. Thence onwards continuous attempts were made to solve the problem of transmitting sketches, pictures, and photographs ; a long list of names of these early workers might be given. But we may well confine our attention at present to two men, Amstutz and Shelford Bidwell, as the ideas of these men were actually the germs of two important pro- cesses which have now given most satisfactory results. The latter made use of the newly dis- covered sensitiveness to light of the metal selenium, the former of the possibility to use the relief in a certain form of photographic image to vary the strength of the electric current. On the lines followed by Bidwell, Ayrton and Perry also made experiments, both therefore utilis- ing selenium at the sending station. Let us suppose that a portrait is to-be telegraphed from this station THE SELENIUM CELL 5 to a distant receiving station. t The portrait is pro- jected on to a screen, where light and shade and varying tones are produced. Now suppose this screen divided up into a thousand square sections, each one the size of a selenium " cell," the cell being an arrangement made with selenium, which varies in its electrical resistance according to the strength of the light illuminating it. This cell is held in one section of the bright image on the screen, then in the next, then in the next, and so on, until finally it has been held in the whole thou- sand sections. But each section is of a different brightness, according to what portion of the image is projected upon it. In each section, therefore, that the cell was held, its electrical resistance varied. Now imagine you could record these variations in resistance on a similar screen at the receiving station. When the selenium cell was held over section i of the image of the screen, its resistance was, let us say, r\ ; using a battery of 100 volts, and neglecting the resistance of any connecting lines, the current at the receiving station would be . Let this regulate, in any imaginable way, r\ the strength of an electric light, which is shining on a similar screen at the receiving station, on the screen being placed a sheet of sensitive photo- graphic paper. Next let the selenium cell be held 6 PHOfO-TELEGRAPHY in the section 2, so that a slightly different part of the image falls upon it, the resistance changing to r 2 , and the current at the receiving station to - ; simultaneously let the electric lamp (whose Y i brilliance has of course changed in the proportion of r\ to r 2 ), shine on section 2 of the receiving screen. If you can imagine this procedure to be carried out over the whole photograph at the send- ing station, the ever-varying electric lamp being shone on always corresponding sections of the photographic paper at the receiving station, the movements being in all cases synchronous, you will be able to see that on developing the sheet of papei a photograph would be obtained, consisting of a thousand square patches of different intensity, which, examined from a distance, would give a representation of the original image projected on the screen. Such a process would in practice be both absurd and impossible, but it enables one to form some conception of the idea of Bidwell and Ayrton and Perry. The image to be telegraphed could quite easily be a photograph printed on a transparent material, such as celluloid, and this print fixed to a revolv- ing glass cylinder, inside which was fixed an electric lamp, whose rays were concentrated so as to pass through one spot on the cylinder to a fixed selenium cell. On then revolving the cylinder SELENIUM DIFFICULTIES 7 and letting it also rise spirally, the pencil of light would traverse different consecutive parts of the picture, and the light falling on the selenium would, of course, vary in strict accordance. Such a method is practically similar to that actually used by Professor Korn, as will be seen on reading the next chapter. Then, again, the current sent to the receiving station, which would depend at each instant on the density of the particular piece of photograph through which the pencil of light was passing, could be utilised to open or close a shutter through which another pencil of light could be admitted to a sen- sitive photographic film. Suppose this film on a cylinder revolving in a precisely similar fashion to the transmitting cylinder, and you have what prac- tically amounts to Professor Korn's receiver. The great practical difficulty arose, however, from the fact that selenium, unlike the feminine mind, could not change rapidly enough ; there are an immense number of different tones in one small strip of a photograph, and the constant changes in illumination were not at all well responded to by the selenium cell . The practical application of the method was destined to await Professor Korn's re- markably ingenious work on the compensation of the " lag " in selenium cells, which only became possible after much very ingenious mathematical and experimental work, Korn is a master mathe- 8 PHOTO-TELEGRAPHY matician, and photo -telegraphy is one instance where somewhat abstruse calculations on paper turned out to be in perfect harmony with practical work. In referring to the methods of Amstutz, I will quote from an interesting article by Mr. William Gamble, that appeared twelve years ago in the first number of Penrose's Pictorial Annual, of which he is the editor. Briefly, he says, the process is this : A photograph in relief (prepared in gelatine) is fixed to something akin to a phonograph cylinder, so that a stylus travels over its surface, rising and falling as the picture passes beneath it. Instead of producing sound, like the phonograph, it is made to vary the strength of an electric current, which passes over a telegraph wire and actuates a similar stylus at the other end, which, bearing on a plate bent round a revolving cylinder, cuts a reproduc- tion of the original, but in a series of parallel lines (the successive " turns " of the cylinders) which gives the effect of a half-tone block. The stylus is sharpened like a graving tool, V-shaped, so that as it cuts deeper it cuts wider, and in printing produces darker or wider lines, Amstutz, in a lengthy letter which the editor of the Annual publishes, describes a method in which a photographic print is made on a metallic sheet, the half-tone of the photograph being broken up into parallel lines, " the photo -message being re- AMSTUTZ AND BELIN g ceived at the distant station in an engraved manner ready for printing." " Theoretically/' he says, " the half-tone system encounters no difficulties whatever. From a prac- tical point it is not available for commercial work." He describes the troubles that would arise from interference effects, owing to the lack of correspon- dence that there would be between the mesh of the half-tone screen and the path travelled by the stylus over the cylinder, and claims that by using the single-line pictures referred to these troubles could be avoided. In all the half-tone photo -telegraphic work single -line pictures are solely used, but at present no satisfactory method has been obtained of engraving the block direct during the reception. Amstutz's idea of using a photographic image in relief, and making the actual relief mechanically vary an electrical resistance, has been successfully followed up by a French inventor named Belin, but he again cannot obtain direct engraving at the receiving end. Direct photo - engraving by telegraphy may "come" some day, but not until that much desired thing has been discovered, the variable relay. The resistance of a telephone line two hundred miles long may be, perhaps, 2,000 ohms. We cannot employ very high voltages, 100 volts being con- sidered very high ; if we divide i oo by 2,000, we io PHOTO-TELEGRAPHY get the maximum amount of current that could be obtained at the receiving station one -twentieth of an ampere ; with '05 ampere and only therefore 5 watts, it would be almost impossible to actuate a graving tool, even to cut into some soft composi- tion. Block -making is so rapidly done in a modern illustrated newspaper office that such a method is not now worth following up. Turning next to Caselli's pan-telegraph, we find him employing a sheet of metal with a sketch or writing drawn upon it in insulating ink ; the sketch on metal was stretched over a curved copper plate, and a similar curved plate was placed at the receiv- ing station, a sheet of paper moistened with potassium ferricyanide solution being stretched over it. The plates were electrically rocked, synchronism being obtained by means of a pen- dulum. A metal stylus traced over the sketch at one end and over the paper at the other, the circuit being completed through the metal plates. At the end of each " rock " the paper and sketch were shifted laterally, so that in each case the stylus travelled over a line parallel to the last line traced. When the sending style touched the metal the current flowed and the ferricyanide was decom- posed, a blue mark being produced. Some excel- lent transmissions of writing, etc., were obtained in this way at a comparatively high rate of speed. The same system was employed by the French tele- THE TELEWRITER n graph engineer, Meyer, except that he used syn- chronously revolving cylinders in place of the curved metal plates. Although the transmission of writing cannot be classed with the telegraphy of photographs, it will be, nevertheless, of interest to describe the tele- writer, which gives a facsimile reproduction at the receiving station of anything written or sketched at the sending station. In writing any letter on paper, the movement of the pen can always be re- solved into horizontal and vertical components ; by making these resolved movements mechanically vary two resistances, currents of two corresponding strengths can be transmitted to a receiving instru- ment ; but three lines are necessary, or two lines and an earth. The two currents when received are used to actuate a V-shaped nib filled with ink, both vertically and horizontally, the resultant move- ment causing the nib to trace over the paper a replica of whatever the transmitter draws with his mechanical " pen." In the telautograph of Grzanna, the two currents corresponding to the vertical and horizontal movements of the transmitting pen are made to actuate a mirror galvanometer, the mirror of which can turn about two axes, so that a spot of light traces the letters or sketch over a sheet of photographic paper. ^These methods are only suitable for transmitting sketches or designs that are drawn at the actual 12 PHOTO-TELEGRAPHY time of transmission. A cartoon was in one instance drawn by Mr. W. K. Haselden in Man- chester and sent by him to the London office of the Daily Mirror, but it was not so satisfactory as the same sketch would have been had it been photographed and then telegraphed to London ; the pencil of the transmitter requires some prac- tice to use it with comfort. A method more recently worked out for the transmission of photographs is that of Charbonelle, a French postal engineer, in which once again the Caselli transmitter is employed, and a series of short currents are transmitted which correspond to the interruptions caused by the insulating lines of a sketch or single -line screen half-tone photograph. He has also endeavoured to transmit by a method that has been put to the test by almost every engineer who has paid any attention to the problem of photo -telegraphy, namely, by causing the deposit of silver (or other substance) in the image of a photographic film to act as the means of varying the current transmitted'. This was very carefully investigated by the author in 1907, about a year before the publication of Charbonelle's patent, but although results of a kind were obtained, the idea was abandoned owing to certain fundamental diffi- culties which will probably never be overcome. In Fig. 2 is seen a diagrammatic representation of a transverse section of the film of an ordinary CONDUCTIVITY OF FILMS 13 photographic negative. Let S be a stylus travel- ling over the film ; now consider any points PQR, it being supposed that the film has been coated 'on metal foil instead of glass or celluloid. If one terminal of a battery be connected to S, the other to the metal foil, current will flow from S to P, in one instance the reduced silver grains form- ing the image being represented by dots. Now suppose the stylus to be at S', where, owing to a light part of the picture, there is much less deposit of silver. Assuming trie film to be of gelatine (in a moist condition), less current will , s - s ' ir ,>, flow from S' to R **p~'~"'' : ' "'-' :: ?" ' : '^ than from S to "p q ^ P, as between S FIG. 2. and P there are many more granules of silver to render the film more conductive. Hence, if the photograph be rotated on a cylinder, and the stylus trace a spiral path over its surface, the current flowing through it to a receiver should vary in accordance with the depth of silver deposit. I also tried using a relief carbon image on copper foil, the gelatine being saturated with a badly conducting medium, so that the current passing from style to copper base would vary inversely as the thickness of the film ; some fair results were obtained in this -way, but the method would be always very uncertain, as the 14 PHOTO-TELEGRAPHY current would pass through the film in the line of least resistance. Charbonelle's receiver is also one that has been suggested by some of the earlier workers ; he passes the received current into a microphone, in the centre of the diaphragm of which is a hardened point ; this point of course vibrates in the same manner as the diaphragm. The microphone is brought down over the cylinder of the receiving apparatus until it presses on an outer sheet of paper wrapped round it ; under this outer paper is, first, a sheet of carbon paper, and second, another sheet of plain paper. As the microphone diaphragm vibrates in response to the interruptions of the current, so the point digs into the outer paper and the mechanical pressure causes a carbon mark on the inner paper. The results are stated to be good, but the method is not likely to be of use for long distances. Berjonneau has worked out a method of trans- mitting half-tone photographs made with a single - line screen, the receiver containing a minute shutter which cuts off or allows to pass the rays from a lamp concentrated on a revolving sensitive film. I Have seen a promising result obtained with his appa- ratus,* but detailed particulars of his system are not yet available. He has, however, made trans- missions over a telegraph line from Paris to Eng- * Shown at Soc. Ing. Civ., Paris. A WIRELESS METHOD 15 hien " in four minutes seven seconds," according to a newspaper report, " and the reproduction at EngHien did not show any signs of lines, and might have been made in the studio of a photographer. 1 ' An ingenious idea for transmission without wires deserves mention here, and has been patented by the inventor, Francesco de' Bernochi, of Turin. The invention can never be of much practical value, and is, in fact, a retrograde one, carrying us back to the early experiments in wireless telephony by means FIG. 3. of light waves. The apparatus can be followed by glancing at Fig. 3. Here Ci is a glass cylinder with a transparent photographic film wrapped round it, and light from the lamp L, after passing through a small portion of it, is reflected by a prism on to a selenium cell SS. This is in series with a battery and the primary of a form of induction coil. As light of different intensities falls on the selenium cell, whose resistance alters in proportion, current is induced in the secondary of the coil and influ- ences an arc lamp, on whose circuit it is shunted ; 16 PHOTO-TELEGRAPHY this arc, the poles of which are represented in the diagram by PP, is placed at the focus of a parabolic reflector RI, and its rays are therefore reflected as a parallel beam to the receiving reflector R 2 . At the focus of this second reflector is a selenium cell Z, whose resistance is altered by the light falling upon it from the reflector. This cell is in series with a battery and mirror galvanometer, light from a lamp N being reflected by the mirror on to a graduated aperture H ; the collected light is focussed upon a photographic film attached to the drum 2, which revolves synchronously with the transmitting cylinder Ci. The idea is an ingenious one, and might be made to work in practice over distances of a few hundred yards, but not more. A suggestion was made on somewhat similar lines to these to the author by Mr. Sharman, in reference to Korn's selenium machines, but for the purposes of wireless tele- graphy the fluctuations in the resistance of the selenium would be used to influence the undamped oscillations given out by a singing arc, and a suit- able receiver would record these fluctuations photographically . One other possible means of receiving from any form of transmitter over short distances deserves reference, inasmuch as it has recently received the attention of Rignoux and Fournier for their pro- posed television apparatus. It is well known that POLARISING RECEIVER 17 if ju, be the refractive index of a substance, and $ the angle of polarisation for that substance, the relation holds good. fji = tan (/>. If a liquid substance contained in a tube BC (Fig. 4) be subjected to a field produced by a coil through which current is passing, its refractive index will be changed ; hence will be changed also. If rays of monochromatic light from a lamp L pass through one nichol prism NI, then