THE ELECTKIC TELEGRAPH. 



How to receive a dispatch at the station, and stop its farther progress. 

 124. How several dispatches may be at the same time sent between 

 various stations on the same line. 125. Secondary lines of wire then 

 used. 126. Recapitulation. 127. Signals by combinations of unequal 

 intervals of transmission and suspension. 128. Key commutator. 

 129. Horological commutator for a current having equal and regular 

 pulsations. 130. Case in which the pulsations are not continuous or 

 regular. 131. No limit to the celerity of the pulsations. 132. 

 Application of a toothed wheel to produce the pulsations. 133. By 

 a sinuous wheel. 134. Method of diverting the current by a short 

 circuit, its application to the alarum. 135. Effects of the current 

 which have been used for signals. 136. Deflection of magnetic needle. 



109. SIKCE all telegraphic signals depend on the power of the agent 

 who makes them, to transmit, control, and modify the current at 

 will, it must be apparent how important it is for those who desire 

 to understand this interesting subject, to comprehend in the first 

 instance the means by which this power is obtained and exercised. 



It is necessary to remember that the current will now along a 

 line of conducting wire so long as, and no longer than, a voltaic 

 battery is interposed at some point on the line, the wire being 

 attached to its poles, and the remote ends of the wire connected 

 with the earth, as explained in (23) and (36), and in that case the 

 current will flow along the wire from earth to earth in such a 

 direction as to enter the battery at the negative, and to leave it at 

 the positive pole, and that provided the battery have adequate 

 force, it does not matter how distant from its poles the points may 

 be at which the wires are connected with the earth. 



If at any point of the line the wire is broken, the current 

 instantly ceases along the entire line. If it be reunited the 

 current is instantly re-established. If the connection of the 

 wire with the poles of the battery be reversed, so that the end 

 which was connected with the positive is transferred to the 

 negative pole, and vice versa, the direction of the current along 

 the entire line is reversed since it must always flow from the 

 positive and to the negative pole. If at any point the wire, being 

 broken, be connected with another wire proceeding to the earth in 

 any other direction, the current will be diverted to the latter wire, 

 deserting its former course. If the wire conducting the current 

 be connected at the same point with two wires both connected with 

 the earth, it will be distributed between the two, the greater part, 

 however, following that wire which offers the easier road to the earth. 



These few principles, which are clear and simple, supply an easy 

 key to the whole art of electro-telegraphy. 



110. The class of mechanical expedients by which the agent 

 who desires to transmit signals is enabled to control and modify 

 the current in the manner here described, are called by the general 

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