ELECTRIC TELEGRAPH. 



attitudes of the arms, as in the French State instruments, or poin- 

 ters directed *to the letters or figures on a dial, as in the railwajf 

 instruments, the celerity of the transmission must be determined 

 by the power of the less able of the two agents, the transmitter 

 and receiver. If the transmitter be able to send the letters more 

 rapidly than the receiver can read and take them down, he must 

 moderate his pace to the limit determined by the power of his cor- 

 respondent. If the receiver be capable of reading and taking 

 down faster than the transmitter is able to send the letters, his 

 superior force is useless. He can only write the dispatch as fast 

 as he receives it. To send dispatches with the greatest advantage 

 of celerity, the agents yoked to corresponding instruments ought 

 to be selected of as nearly equal ability as possible, since the 

 slower of a pair necessarily neutralises the superior skill of his 

 fellow, and the dispatch would proceed with equal celerity if he 

 were yoked with a less able correspondent. 



As quickness of hand is essential to the transmitter, quickness 

 of eye is necessary to the receiver. 



227. In all forms of telegraph which express the letters by 

 signals, such as the needle telegraph, and the French State tele- 

 graph, a certain pause is necessary between letter and letter, to 

 prevent the signals being confounded one with another. In the 

 single needle instrument, the letters being expressed by from one 

 to four deflections of the needle, and in the double needle, from 

 one to two, the mean time of each letter is that of two and a half 

 deflections in the one, and one and a half in the other, the intervals 

 between letter'and letter being the same in both. Owing to the 

 slowness of transmission of the single needle instrument, it is 

 only used between secondary stations, where there is but little 

 business. It must, however, be remembered, in comparing the 

 relative celerity of different instruments, that the double needle 

 instrument, as well as the French State telegraph, is, in fact, two 

 independent telegraphs, having not only separate and independent 

 transmitting and indicating apparatus, with their respective 

 accessories, batteries, &c., but separate and independent conduct- 

 ing wires. It is, in effect, as if two equally powerful and inde- 

 pendent steam engines were united in the same work, in order to 

 obtain double power. 



228. In 1850, Mr. Walker made some calculations, with the 

 view to determine the average celerity of transmission at that 

 time with the double needle instrument in the hands of compe- 

 tent operators, and published the results in his work on electric 

 telegraph manipulation. Eleven messages were timed, all of 

 more than the usual length, the shortest consisting of 73 and the 

 longest of 364 words. The total number of words was 2638, and, 



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