;6S 



NA TURE 



[October 5, 1905 



TrP/r-IfA'/T/.VG Bl" TELEGRAPH.' 

 (^NE of the most interesting papers read during the last 

 ^-^ session of the Institution of Electrical Engineers was 

 that by Mr. Donald Murray on setting type by telegraph. 

 Strictly speaking, the title of the paper is something of a 

 misnomer, as the apparatus described by Mr. Murray was 

 constructed for type-writing rather than type-setting; but 

 as the principle is equally applicable to the latter process, 

 it is unnecessary to be too critical. This is specially the 

 case as the instruments and method were originally de- 



signed for the automatic telegraphic operation of linotype 

 machines, and it was only because commercial consider- 

 ations indicated the greater importance of the solution of 

 the problem of telegraphic type-writing that attention was 

 more particularly devoted to this question. 



The problem which has to be solved is one of consider- 

 able complexity, as will readily be realised when its 

 essential characteristics are considered. A message handed 

 in at the transmitting station has to be translated into a 

 series of signals which can be telegraphically transmitted 

 over a single telegraph wire. These 

 signals, on arriving at the receiving 

 station, must actuate a receiving 

 mechanism in such a manner that a 

 particular set of signals produces a 

 certain definite movement of the 

 mechanism ; thus the signals corre- 

 sponding to the letter " a " must cause 

 the striking (or equivalent) of the type- 

 writer key " a," the signals corre- 

 sponding to a notification of the end 

 of a line must cause the shifting of 

 the type-writer carriage ready for a 

 new line, and so on. Now it is obvious 

 that the signals as they are transmitted 

 over the telegraph vvire can only differ 

 from each other by virtue either of 

 their time arrangement or their magni- 

 tude. Each set of signals (correspond- 

 ing to a letter) must be made up of 

 one or more pulses of current, and one 

 letter can onlv be distinguished from 

 another by virtue of the pulses for the 

 one being different in magnitude from 

 those for the other, bv their follow- 

 ing one another at different intervals 

 of time, or by their lasting for different periods of 

 time ; of course, also, a combination of any two or of 

 all three of these may be used. It is not possible for 

 the telegraphic signals to be differentiated in space 

 unless more than one wire is used to connect the two 

 stations. It is equally clear that the distinction between 

 the signals in their final form is one of space, and this is 



1 "Setting Tvpe by Telegraph." By Dona'd Murray. {/flurtial 

 cj the InstttutioH 0/ Electrical Engineers, vol. xxxlv., pp. 555. 

 1905)- 



SO whether we consider the ultimate result, that is to say, 

 the printed letter, or merely the alterations produced in 

 the space relationship of the various parts of the printing 

 mechanism which causes that mechanism instantaneously to 

 print a particular letter. Thus we may say that what a 

 type-writing telegraph has to do is the following : — it has 

 to receive a message and translate it into a series of time 

 or magnitude signals, to transmit these signals electrically 

 over a wire, and to re-translate them into a series of space 

 signals. 



We have had occasion during recent years to describe 

 several systems of telegraphy which 

 aim at doing much the same thing as 

 the Murray telegraph attempts, and it 

 is of interest to compare the trans- 

 mission methods used in these. Thus 

 in the telautograph (see Nature, vol. 

 Ixiv. p. 107) the actual handwriting of 

 the original message is transmitted and 

 reproduced, and this is done by a com- 

 bination of space and magnitude 

 signals. Two wires are used, and 

 current pulses of varying magnitudes 

 sent along them which reproduce at 

 the receiving end the motion of a pen 

 at the transmitting station. Here the 

 time element of the signals has no 

 effect, and a letter is reproduced 

 equally if it be traced in one second 

 or in one hour. In the Pollak-Virag 

 svstem (see Nature, vol. Ixiv. p. 7) 

 the telegraphic signals produce the 

 motion of a beam of light which re- 

 cords in Roman letters the message 

 transmitted. In this system the tele- 

 graphic signals differ from one another in their space 

 relation and their duration. In the Murray system the 

 signals differ from one another in their time relation. 



We have pointed out that the first process is the trans- 

 lation of the message into a series of time signals, and 

 for this purpose a time signal alphabet has to be chosen. 

 Though this may at first sight seem a matter of secondary 

 importance, it is in reality hardly too much to say that 

 upon the suitability of the alphabet selected will depend, 

 more than upon anything else, the chances of success 



Fig. 2.— Single-1 



of the system. This fact has been thoroughly realised by 

 Mr. Murray and others who have worked upon this 

 problem, with the result that an alphabet has been finally 

 devised which seems to possess in the greatest degree 

 possible all the more important advantages. In it every 

 letter or other signal which has to be transmitted is re- 

 presented by a series of five time signals ; the alphabet is 

 therefore an " equal letter alphabet," that is to say, each 

 letter is composed of the same number of signal units (five 

 in this case). The average nuinber of units per letter is, of 



NO. 1875, VOL. 72] 



