October 5, 1905 J 



NATURE 



569 



course, five ; in the Morse alphabet the average number is 

 thirteen ; there is therefore an apparent advantage in time 

 over the Morse code, but this may be more apparent than 

 real, as the unequal length of the letters in the Morse 

 code enables the shorter ones to be chosen for those letters 

 occurring with the greatest frequency (such as E and T), 

 so that the average number of units per message may be 



TRANSMITTING STATION 



yiBRATOfi) 



TRANSLATOR 



RECEIVING STATION 



Printi-ig Telegraph Sy 



less than in an equal letter alphabet having a smaller 

 average number of units per letter. Thus experience has 

 shown that the actual average number of units per letter 

 with the Morse code is only eight instead of thirteen. It 

 must be remembered, also, that the Morse code is intended 

 primarily for hand signalling, and consequently when time 

 intervals are used the difference between any two which 

 have to be distinguished manually or by ear must be fairly 

 great. Thus the Morse dot consists of one unit, the Morse 

 dash of three ; were two units used for the dash instead 

 of three, the distinction bctv/een the dash and dot would 

 not be sufficiently marked. With machine telegraphy, on 

 the other hand, there is no need to make such a great 

 differentiation between the signals, as time intervals of 

 one, two, three, and more units can all be distinguished, 

 and in consequence it is possible to devise a shorter 

 alphabet than the Morse code. It is not to be denied, 

 however, that the use of a new alphabet is undoubtedly 

 a disadvantage from the practical point of view, as it has 

 to be learnt by the operators. This drawback is 

 minimised by the fact that the operator does not print 

 each signal separately as in operating a transmitting key ; 

 but it is nevertheless desirable, if not essential, that he 

 should be able to read the message when printed on the 

 transmitting tape. 



To turn now to the apparatus used in the Murray 

 system ; the first operation, as in all automatic telegraph 

 systems, is to punch the message to be transmitted on a 

 paoer strip or " tape." This is done by means of a key- 

 board instrument of the ordinary type-writer form shown, 

 with the cover removed, in Fig. i. On the tape will be 

 noticed a double row of holes, which can be seen more 

 distinctly in Fig. 4 ; the row of small holes serves 

 only to feed the tape forward, both in this machine 

 and in the transmitter; the larger holes are the signals 

 punched in the tape. The actual perforator can be seen 

 in front; it is worked by an electromagnet which 

 punches the necessary holes on the forward stroke and 

 moves the tape one letter space (five holes) forward on 

 its back stroke. On the right can be seen a lever which 

 enables the tape to be pulled back letter by letter to make 



corrections; these are made by punching five holes, thus 

 blotting out all the holes already punched, this signal (of 

 five holes) leaving the receiving mechanism unaffected. 

 It is thus possible to wipe out any part of the message 

 incorrectlv written on the tape, and so produce a tape 

 which will give an absolutely correct message when trans- 

 mitted : this is facilitated by the fact that the operator 

 can see the tape as it is perforated, 

 letter by letter. The speed at which 

 this perforator can be worked is 

 about 120 letters (twenty words) a 

 minute. The transmission can be 

 carried on five or six times as 

 rapidly, so that five or six operators 

 working at these perforators can 

 produce enough tape to keep the 

 transmission line full. 



The automatic transmitter is 

 shown in Fig. 2, and diagram- 

 matically in Fig. 3 (collector). The 

 tape is fed forward in the usual way 

 by the star-wheel 15, passing across 

 the end of an upright rod i. This 

 rod is pivoted as shown to the 

 system of levers which oscillate 

 about the centre 4, being kept in 

 oscillation by the eccentric wheel 5, 

 and making one oscillation for every 

 unit on the tape. If this unit is a 

 hole, the rod i enters this hole, the 

 end 2 of the lever 2-9 is raised and 

 the end 9 lowered, whereby the 

 oscillation of the lever 3 brings the 

 end 9 against the bar 11, thus push- 

 ing the contact lever 13 against con- 

 tact 18. Here it remains until the 

 next oscillation, and if this is the 

 same as before, due to a second 

 hole in the tape, it is not disturbed. 

 It will thus be seen that successive 

 signals of the same kind (either successive holes or 

 successive spaces) are transmitted, not as intermittent, 

 but as continuous signals. But if there follows a space 

 in the tape the rod i cannot rise to its full height, 

 the lever 2-9 is kept down at the end 2 and raised at 

 the end 9, which comes in consequence against the rod 

 10 and forces the contact lever 13 over against contact 

 19, thereby brealiing the punching current and send- 

 ing spacing current into the line. The whole apparatus 

 is driven by a phonic wheel motor in the usual way, the 

 vibrating reed 23 sending currents alternately to the 

 magnets 24 and 25, which keep the armature 26 in rota- 

 tion. This is geared directly to the star-wheel 15, which 

 has ten teeth, and is itself geared in the ratio of 10 : i 

 to the eccentric wheel 5, so that the latter makes, 

 as alreadv stated, one revolution for everv unit of the 



tape. 

 Xow 



let 



follow the message to its arrival at the 



0000 0;0 000 0\0 000 0:0 000 0;0 O O O O'.O j 



OQ pop I , : O O: : :OQ : Iq Q ; i 



^ys ds w M 



J'm ^^ m i^M^; 



receiving station, where the signals are caused to produce 

 a second perforated tape, the exact duplicate of the first, 

 by means of the mechanism grouped together in Fig. 3 

 under the title " distributor." The tape is fed forward 

 unit by unit by means of the spacing magnet which 

 operates the escapement 31, and holes are punched in the 



NO. 1S75, VOL. 72] 



