August i8, 1910J 



NATURE 



!2I 



words and messages ; squares of different densities recom- 

 bined, in correct position, form a photograph. 



I propose to deal witli the more practical system first, 

 which, as already pointed out, is perhaps the less interest- 

 ing from the theoretical point of view. The telectrograph 

 svstem has been employed by the Daily Mirror for the 

 transmission of photographs since July, 1909, and has 

 been worked very regularly between Paris and London 

 and Manchester and London. 



Instances of its use may be recognised in the publica- 

 tion of photographs taken in court in the recent Steinheil 

 case at Paris, when photographs of witnesses or prisoners 

 were sometimes received in London actually before the 

 court rose at which they were taken, a clear day being 

 gained in the time of publication. 



The method of telegraphing photographs that has been 

 employed on a large scale by the Daily Mirror may be 

 called a practical modification of several early attempts. 



-Fashion Plate Tr 



litted by Prof. Korn's Telautograph. 



The effect of an electric current to discolour certain suit- 

 able electrolytes or to set free an element or ion that can 

 be used to form with a second substance a coloured pro- 

 duct was employed in many early forms of instruments 

 for telegraphing writing, &c. If we break up a photo- 

 graphic image in the way already described into lines 

 which interrupt the current for periods depending on their 

 width, these interrupted currents can be used at the receiv- 

 ing station to form coloured marks, which join up en 

 masse to form a new image. My telectrographic process 

 is thus briefly as follows : — 



.\t the sending station we have a metal drum revolving 

 under an iridium stylus, to the drum being attached a 

 half-tone photograph printed on lead foil. Current flows 

 through the photographic image to the line, and thence to 

 ,i,r. receiver. The receiver consists of a similar revolving 



Ml drum, over which a platinum stylus traces. Every 

 the transmitter style comes in contact with a clear 



:; of the metal foil, current flows to the receiver, and 



!'lack or coloured dot or mark appears on the chemical 



NO. 2129, VOL. 84] 



paper. But you will readily understand that if our repro- 

 duction — built up of these little marks, which have to be 

 made at the rate of some two hundred per second — is to 

 be accurate, each mark must be only exactly as long, in 

 proportion, as the clear metal space traversed bv the 

 stylus. 



It will be easier to explain the system by means of the 

 rough diagram shown in the figure (Fig. 4). The trans- 

 mitting instrument is shown on the left, the receiver on the 

 right. A metal drum is revolved by a motor, one revolution 

 every two seconds ; over this a metal stylus or needle traces 

 a spiral path in the same way as a phonograph. On the 

 drum is fixed a half-tone photograph broken up into lines, 

 and printed in fish-glue upon a sheet of lead foil. I will 

 show one of these line photographs on the screen, and you 

 will see that the light and shade of the picture are made 

 up of masses of thinner or thicker lines, with clear spaces 

 in between. 



-As the stylus traces over such a photograph, its contact 

 with the metal base is interrupted every time one of these 

 fish-glue lines comes beneath it, and for such a time as 

 depends, of course, on the width of the line. The trans- 

 mitting instrument thus sends into the telegraph lines a 

 series of electric currents the periods of duration of which 

 are determined by the width of th'- lines composing the 

 photograph. 



.A similar stylus, S^, traces 

 an e.xactly similar path o\er 

 a revolving drum in the re 

 ceiving instrument, but round 

 this drum is wrapped a piece 

 of absorbent paper impret; 

 nated with a colourless '.olu- 

 tion, which turns black or 

 brown when decomposed b\ 

 an electric current. 



What happens, then, is that 

 every brief current which 

 passes through the paper 

 causes a mark to appear on 

 it. The w-idth of the mark 

 depends on the duration of 

 the current — or should do — 

 so that you will see that these 

 marks gradually combine to 

 recompose the photographic 

 image. 



This method is all very 

 well in the laboratory, but 

 when we come to try it 

 over a long distance the 

 capacity of the line at once 

 causes serious interference, 

 if a current be sent to some apparatus, such as a 

 telegraph, from a distance, the current having to pass 

 through long wires the capacity of which is appreciable, 

 a certain time is taken for the current to charge the line, 

 and the line discharges itself into the apparatus with com- 

 parative slowness. If the circuit be closed by means of a 

 Morse key, the time of contact at the key being a si.xth 

 of a second — a common time of duration of a short tap — 

 the discharge of current from the cable would be consider- 

 ably longer than one-sixth of a second. When, therefore, 

 we are sending signals through the line at the rate of 175 

 per second, it is not difficult to see that every signal will 

 riin into the next dozen or so at the receiving apparatus, 

 and the result will be a hopelessly confused mass of over- 

 lapping marks. This is well illustrated in Fig. 5, where 

 .■\ shows a series of taps passed through a cable of high 

 capacity into the telectrograph receiver ; instead of getting 

 a series of sharp dots or short lines, we get elongated lines 

 ending off in tails. Without the capacity, we get the short 

 lines as shown in the B series. These short, definite lines 

 are again obtained, even when the capacity is present, in 

 series C ; but in this case I had shunted on to the receiver 

 what I have termed the line balancer, a modified form of 

 shunt apparatus embodying the principles of wiping out 

 residuary currents from the cable in the way frequently 

 made use of in duplex telegraphy. 



The use of this apparatus has rendered commercial the 

 old ideas of telegraphing by the electrolytic method, and 



"ic. ^. — Photograph Wired from 

 Pari.s to London by the Author's 

 Telectrograph. 



It 



well known that 



