TRENCH RAILWAY TELEGRAPH. 



the handle is carried round the fixed dial, the moveable dial behind 

 is carried round with it. 



Upon the upper part of the board carrying the dial are placed 

 two supplementary commutators, L and I/, the hands of which 

 play upon the contact-pieces, s, s, E, and s', s', E', as well as upon 

 an oblong plate of metal, upon which the words " COMMUNICATION 

 DZRECTE " are engraved. 



The terminals c and z communicate with the copper and zinc 

 ends of the battery, or what is the same, with its positive and 



S s E 



negative poles ; T communicates with the earth. The contact 

 pieces s s' are connected with alarums, n it with the indicators, 

 and the axes of the arms L I/ with the line-wires. The dotted 

 lines indicate the positions of slips of metal inlaid in the back of 

 the frame, by which the several pieces are put in metallic 

 connection one with another. 



After the general explanation of the manner in which the course 

 of the current is in all cases governed, it will not be necessary 

 here to explain the application of these commutating apparatus, 

 which are nothing more than particular applications of the general 

 principle so fully developed in 111. 



A perspective view of the commutator and indicating apparatus 

 mounted in the same case, is given in fig. 74 (p. 17). The com- 

 mutator is fixed upon a horizontal desk, that being the most 

 convenient position for its easy and rapid manipulation. The 



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