558 THE APPLICATIONS OF PHYSICAL FORCES. [BOOK y. 



Figure 356 represents the indicator, which consists of two sym- 

 metrical and independent apparatus, each corresponding to one of the 

 indicating needles. These needles, half black and half white, can 

 take eight positions about their centres, two horizontal, two vertical, 

 and four at angles of 45 with each of the others, which gives 64 dis- 

 posable signals. The mechanism of the indicator has much analogy 

 with that of Breguet's dial telegraph which we shall presently describe 



in detail. By turning the handle 

 M of the manipulator, which is 

 in duplicate, and giving to it 

 one of the eight positions corre- 

 sponding to the eight notches of 

 a fixed wheel, another wheel is 

 made to move which is mounted 

 on the axis of the handle, on the 

 plane of which is traced a hollow 

 sinuous furrow. The spring B c 

 then takes either the position 

 seen in the figure, and then the 

 piece I touches the metallic piece 

 v, or a position nearer the centre, 

 I in this case goes over and touches 

 the -piece v' on the left. The two 

 pieces v and v are insulated by a 

 piece of ivory from the metallic 



part of the manipulator, in which end respectively the wires of the 

 battery, the line, and the indicator. There is thus sometimes a 

 passage, sometimes an interruption of the current, which produces 

 in the indicator the corresponding movements of the indicating 

 needle. 



The above is the vocabulary adopted for the French needle tele- 

 graph. The horizontal mark is common to all the signals and 

 requires no operation. Seven letters, A, B, c, E, F, G, w, only require 

 the action of the left hand manipulator, six letters, H, I, K, M, K, o, 

 only that of the right hand manipulator. The thirteen other signs 

 require the simultaneous movement of the two manipulators and the 

 two apparatus. This system has been for a long time employed by 

 the authorities of the French telegraphic lines. 



A 



B 



G 



D 



E 



F 



G 



H 



I 



J 



K 



L 



M 



N 

 

 P 



II 



s 



T 



U 

 V 



w 



X 

 Y 



Z 



FIG. 358. Vocabulary of Foy and Breguet's 

 needle telegraph. 



