THE ELECTRIC TELEGRAPH. 



straight, the length of the zigzag and straight parts being varied 

 at the will of the operator at s. 



How these subserve to telegraphic purposes will be presently 

 more fully explained. 



154. In the same manner, if a toothed wheel, moved by the 

 agent at s, produce a pulsation of the current by the passage of 

 each successive tooth, these pulsations will produce simultaneous 

 oscillations of the lever og, at the station s", and if these oscilla- 

 tions act upon the anchor of an escapement wheel attached to 

 clock-work at s", that wheel will be advanced in its revolution, 

 tooth for tooth, with the wheel at s, and if each of these wheels 

 govern the motions of hands upon dial plates, like the hands of a 

 clock, the hand of the dial at s" will have the same motion exactly 

 as the hand on the dial at s, so that if at the commencement of 

 the motion both hands point to the same figure or letter of the 

 dial, they will continue, moving together, to point always to the 

 same figures or letters. 



Thus if the operator at s desire to direct the hand on the dial at 

 s", to the hour of 3 or 5, he will only have to turn the hand upon 

 the dial, at his own station, to the one or the other of these hours. 



It will presently also be apparent how important this is in the 

 art of electro-telegraphy. 



155. If the lever og, fig. 58, be connected with the tongue of 

 an alarum- bell, so that when og is put into vibration the bell will 

 ring, and will continue to ring so long as the vibration is con- 

 tinued, it is evident that the operator at s can, at will, ring a bell 

 at s", by producing pulsations of the current in any of the ways 

 already described. 



An operator at s" may in like manner ring a bell at s. 



By this mutual power of ringing bells, each operator can call 

 the attention of the other, when he is about to transmit a dis- 

 patch, and the other by ringing in answer can signify that he is 

 prepared to receive the dispatch, as already stated. 



156. If the lever og were in connection with the lock or other 

 mechanism, by which the powder charging a cannon is fired, the 

 operator at T could at will discharge a cannon at E, no matter 

 what may be the distance of E from T. 



157. It will be observed that when a bell is rung, or any similar 

 signal produced at the station s", by means of an electric current 

 transmitted from a distant station, s, it is not directly the force of 

 the current which acts upon the object by which the signal is 

 made. The current is only indirectly engaged, producing the 

 result by liberating the mechanism which makes the signal and 

 leaving the force which moves it free to act. Thus in the most 

 usual case of a bell, it is acted upon while it rings, not by the 



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