THE ELECTRIC TELEGRAPH. 



with single deflections and with each other, a greater number of 

 different signals can be obtained than are sufficient to express the 

 letters and numerals, each being made in the time necessary for 

 two deflections of a single needle. 



A front view of a double needle telegraph is given in fig. 68 

 (vol. iii. p. 177). 



The small case at the top contains the alarum, and the small 

 handle at the side of the large case is the commutator by which the 

 current is turned on and off the alarum. The two large handles 

 which appear in front are those of the commutators, which produce 

 the changes of direction of the current, and when inclined to the 

 right or left the needles acted on by the current assume a like 

 position. 



FEEXCH STATE TELEGEAPH. 



182. When T the establishment of lines of electric telegraphs 

 was proposed in France, the old aerial telegraph was, and had been 

 for more than half a century, in operation, and formed a depart- 

 ment in the public administration of considerable importance, 

 employing an extensive body of agents, dispersed throughout the 

 country, most of whom were specially instructed and qualified for 

 the business. 



The commission appointed by the government required that the 

 electro-telegraphic instruments should exhibit the same signals as 

 had been already used in the case of the former telegraph. 



The old telegraph consisted of a long straight bar, E E', fig. 69, 

 called a regulator, to the extremities of which two shorter bars, 

 r r', called indicators, were attached by pins or pivots, so that 

 each indicator was capable of turning on its pivot, so as to make 

 any desired angle with the regulator. 



Fig. 69. 



"X / 



"' IT'' i P 



If we suppose the circle described by each indicator to be divided 

 into eight equal arcs of 45, and that any convenient mechanism 

 is provided, by which the agent who conveys the signals can at 

 will give to each indicator any of these eight positions, each indi- 

 cator would be capable of making eight signals, and by combining 

 these in pairs, the two indicators worked together would be 

 capable of giving sixty-four signals. 



It is evident that even this large number of signals might be 

 14 



