70 THE ELECTRIC TELEGRAPH. 



When the current is reversed the polarity, and therefore the 

 deflection, is also changed. 



53. Kramer's Pointer Telegraph* The different telegraphs 

 which have hitherto been mentioned are worked by sending 

 currents of electricity from the transmitting station, either 

 from a galvanic battery or from an induction apparatus. As 

 soon as the signal is given, or the work done, the current is 

 cut off, and the line becomes inactive. The reverse of this 

 mode of operation was introduced by Kramer, in his dial- 

 telegraph, and subsequently by Frischen, for working the 

 Morse instruments on the lines under his charge. In both 

 these systems the current of a galvanic battery circulates 

 continually in the line, and attracts, when at rest, the arma- 

 ture of an electro-magnet at the receiving station. On 

 breaking the line at any point the armature falls off, and 

 remains off until the battery circuit is closed again. 



With the system of currents transmitted for each signal, 

 it is obvious that a separate battery is required for each 

 station. This is not the case when the system of closed 

 circuit is used ; because an interruption in any point must 

 be followed by the same effect on the armatures of all the 

 electro-magnets in the circuit. 



The exterior of Kramer's apparatus differs in appearance 

 very little from that of Siemens and Halske's. It consists of 

 a round dial, with thirty keys on the circumference, numbered 

 from to 29, inclusive. An inner circle is marked, in cor- 

 responding sections, with the letters of the alphabet irregu- 

 larly placed, and a third circle, concentric with the others, 

 contains a double row of numerals from 1 to 9, and some 

 other figures and blanks. 



The interior of the apparatus is shown in Fig. 36. Two 

 circular plates of metal are connected together by means of 

 three pillars near their periphery; through their centres 

 passes the axis c of the pointer z z seen on the dial. This 

 axis carries a scape- wheel, r, and a tooth- wheel, R; it is 

 turned by the tooth-wheel H engaging with its pinion 3. 

 On the axis of the wheel H is a pinion locking into a tooth- 

 * Der Elektro-magnetische Telegraph. ScheUen, p. 195. 



