ELECTRIC TELEGRAPH. 



Let us now imagine the message thus completely inscribed on the 

 perforated ribbon of paper. This ribbon is again rolled as at 

 first upon a roller, and it is now placed on an axle attached to the 

 machinery of the telegraph. 



The extremity of the perforated ribbon at which the message 

 commences is now carried over a metallic roller, which is in con- 

 nexion with the positive pole of the galvanic battery. It is 

 pressed upon this roller, as represented in fig. 88, by a small 



Fig. 83. 



metallic spring, terminating in points like the teeth of a comb, 

 the breadth of which is less than that of the perforations in the 

 paper. This metallic spring is connected with the conducting 

 wire which passes from the station of departure to the stations of 

 arrival. When the metallic spring falls into the perforations of 

 the ribbon of paper as the latter passes over the roller, the 

 galvanic circuit is completed by the metallic contact of the spring 

 with the roller ; but when those parts of the ribbon which are not 

 perforated pass between the spring and the roller, the galvanic 

 circuit is broken and the current is interrupted. 



A motion of rotation, the speed of which can be regulated at 

 discretion, is imparted to the metallic roller by clockwork or other 

 means, so that the ribbon of paper is made to pass rapidly between 

 it and the metallic spring, and, as it passes, this metallic spring 

 falls successively into the perforations on the paper. By this 

 means the galvanic circuit is alternately completed and broken, 

 and the current passes during intervals corresponding precisely to 

 the perforations in the paper. In this manner the successive 

 intervals of the transmission of the current are made to correspond 

 precisely with the perforated characters expressive of the message, 

 and the same succession of intervals of transmission and suspension 

 will affect the writing apparatus at the stations of arrival in the 

 manner already described. 



214. Now there is no limit to the speed with which this process 

 can be executed, nor can there be an error, provided only that 

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