Figure 19. — VVheatstone and Cooke's local circuit (including 

 relay and call alarm) for their 1837 telegraph. From G. B. 

 Prescott, History, Theory, and Practice of the Electric Telegraph, 

 Boston, i860, p. 414. 



proposal to connect all government buildings in Eng- 

 land by a network of telegraph lines. The telegraph 

 system between London and Slough was the first one 

 in England to be opened to public service. The ef- 

 fectiveness of communicating by telegraph was proved 

 during the troubled times of 1848 and during the 

 Crimean War. In the 1850's telegraph lines spread 

 rapidly throughout the continent and Great Britain, 

 and by April 1855 London could communicate directly 

 with Sebastopol. 



Wheatstone and Cooke also invented another kind 

 of telegraph instrument, known as the dial telegraph. 

 The first version of this system, worked out by 

 Cooke in 1836, was based upon two synchronous m^e- 

 chanical clocks, the one at the transmitting station 

 indicating the sam.e letter as the one at the receiving 

 station. The transmitting station closed the circuit 

 and permitted the lettered dial on both clocks to turn 

 until the letter desired was indicated at the transmit- 

 ter; whereupon the circuit was opened and the clocks 

 stopped. Since the clocks were synchronized, the 

 receiving one would stop at the same letter as the 

 transmitting one. The transmitting station would then 

 perform the same operations for the next letter and 

 so on. 



This synchronous system was difficult to reduce to 

 practice, so Wheatstone and Cooke patented another 

 version of a dial telegraph on January 21, 1840 

 (British patent 8345). Li this case the dial at the 



receiver was dri\-en b\" the transmitting dial instead 

 of being controlled in its motion at the receiving 

 station. Moving an indicator over the dial at the 

 transmitting station sent a number of pulses down the 

 line according to the number of letters passed over. 

 These pulses released an escapement, allowing a 

 weight-driven pointer to turn until the desired letter 

 was indicated. This system was called the "step-by- 

 step" dial telegraph (figs. 23, 24). The speech by 

 Queen Victoria that opened Parliament in 1845 was 

 sent at a rate of fi\'e words per minute by this system.'^ 

 In 1858 Wheatstone modified the dial telegraph by 

 using a magneto to provide the pulses (British patent 

 1241, August 2, 1858). This form of the dial instru- 

 ment was quite popular with the British for the re- 

 mainder of the 19th century. The ABC instrument 

 (fig. 25), as Wheatstone's dial telegraph usually was 

 called, had an average speed of about five words per 

 minute; it was used to connect small towns where 

 traffic was light and that were on circuits of not more 

 than four stations. As late as 1920 there were more 

 than 1,000 ABC units still in use. Apparently, the 

 reason for the survival was the simplicity of operation. 

 Edward Davy, an English competitor of Wheatstone 

 and Cooke, came very close to creating a practical 



23 "The London and Portsmouth Electric Telegraph," Me- 

 chanics' Magazine, London, February 8, 1845, vol. 42, p. 96. 



PAPER 29: DEVELOPMENT OF ELECTRICAL TECHNOLOGY IN THE 19TH CENTURY: II 



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