THE ELECTRIC TELEGRAPH. 



When the wheel is made to revolve, the spring / comes alter- 

 nately into contact with the conducting arcs of the one and of the 

 other disc. Another similar spring is applied to another part of 

 the edge of the wheel, so as to be in contact with the conducting 

 arcs of the upper disc, while the spring i j is in contact with those 

 of the lower, and vice versa. 



One of the two discs is in connection with the copper, and the 

 other with the zinc end of the battery, so that one may be con- 

 sidered as its positive and the other as its negative pole. One of 

 the springs is in connection with one end, and the other with the 

 other end of the conducting wire, which forms the coils, and 

 which passes along the telegraphic line. By causing the wheel 

 to revolve, therefore, the conducting wire will be alternately 

 connected with contrary poles of the battery, and the current 

 upon it will be reversed. 



If the edge of the wheel be divided into ten equal parts by the 

 conducting arcs, this reversion will take place ten times in each 

 revolution, and if a revolution be imparted to the wheel in each 

 second, the current will be reversed ten times per second. 



In the apparatus of Lippens the oscillations thus imparted to 

 the armature, g g', fig. 78, are made to act by the intervention of 

 toothed wheels upon the indicating hand which moves upon the 

 dial around which the letters are engraved, as in the French tele- 

 graph, and this hand is moved from letter to letter in the same 

 manner as in the French railway telegraph and that of Siemens. 



Upon the axle of the commutating wheel above described a 

 winch is fixed by which the agent who transmits the despatch 

 turns it. 



A plan of this instrument is drawn in fig. 80. The handle of 

 the commutator B B' is keyed upon the axis of the wheel already 

 described, which is under the table of the instrument. This 

 wheel, and the springs which press upon it, are indicated in 

 the figure. The handles Q Q are those by which the current is 

 conducted from the up or down line through the indicating 

 apparatus, or through the alarum, as already explained in the 

 case of the German telegraph. Several other batteries are provided 

 for establishing connections with the line wires, the battery poles, 

 the alarums, and the earth, and differ in nothing essential from 

 similar adjustments in other telegraphic instruments. 



204. When the agent at any station, s, desires to transmit a 

 despatch to any other station or stations, s', he first, as in other 

 telegraphs, calls the attention of the agents at s' by means of 

 the alarum. The current being then directed through the instru- 

 ments severally by means of the adjustments provided for that 

 purpose, the transmitting agent at s turns the handle B B' of his 

 36 



