THE ELECTRIC TELEGRAPH. 



In each instrument the armature is in connection with a toothed 

 wheel, upon the axis of which the hand m n (fig. 76) is keyed, so 

 that each vibration of the armature puts forward one tooth of the 

 wheel, and advances the hand n from one letter to another. 



195. Upon comparing this arrangement with that of the French 

 telegraph, it will be perceived that here the mainspring and wheel- 

 work which moves the indicator are altogether omitted, and the 

 armature of the electro-magnet, which in the French instrument 

 only regulates the motion of the indicator, here both moves and 

 regulates it. In fine, the armature here discharges at once the 

 functions of the mainspring, and of the pendulum of a clock. 



It will also be observed that the manipulation of the transmitting 

 agent, by which he moves the indicators on the dials of the distant 

 stations, is dispensed with, the current itself, through the inter- 

 vention of the armature of the electro-magnet, imparting to the 

 indicator a constant motion of rotation without any manipulation 

 -whatever. 



That part only of the manipulation by which the indicator is 

 stopped for a moment successively at the letters of the word intended 

 to be transmitted, is retained, and tjiat is effected by the action of 

 the keys surrounding the dial. 



196. Under the dial, a radius or arm is keyed upon the axis on 

 which the indicating hand is fixed, so as to be always immediately 

 under that hand and parallel to it, revolving simultaneously with it. 

 This radius is a little longer than the indicating hand, and extends 

 under the keys surrounding the dial. From the under-surface of 

 each key a pin projects, the length of which is such that when the 

 key is not pressed down, the radius passes freely under it ; but 

 when the key is pressed down, the pin comes in the way of the 

 radius, and stops it when the indicating hand n arrives at the 

 letter engraved on the key. By the action of the same pin the 

 armature o g (fig. 77) of the electro-magnet is arrested in its return 

 from V to t, so as to be prevented from arriving at t. The current, 

 therefore, is prevented from being re-established on the line-wire, 

 as it would be if g o were permitted to come into contact with t . 



Thus it will be understood how by putting down a key the two 

 desired effects are produced. 1st, the stoppage of the indicating 

 needles at the letter engraved on the key of the indicator on which 

 such key is put down ; and 2nd, the simultaneous suspension of 

 the current along the entire telegraphic line, by which the indi- 

 cating needles of all other instruments are stopped at the same 

 letter. 



197. This apparatus, compared with the French telegraph, to 

 which it has an obvious analogy, has the advantage of greater 

 simplicity. By dispensing with the mainspring and its necessary 



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