240 



SCIENTIFIC RECREATIONS. 



the two plates or springs, which, when not in use, are always pressed against 

 the connector, K, which is a cross-piece on the top of the handle, keeping the 

 London needle in circuit with the York battery, and vice versa. As soon 

 as London uses his handle, it presses the spring-plate, and puts his needle 

 out of the York circuit, the current he sets up sending York needle to the 

 right or left, as the case maybe. The second wire connecting the left York 

 plate with the right London plate is, it will be seen, not carried along like 

 the first wire. Use is made in this case of the cpnducting power of the 

 earth itself, plates from the wires being buried many feet below the surface 

 at London and York. When London wishes to speak to York, he first 

 signifies his intention of so doing by ringing York's alarum. This he effects 

 by sending a current through an electro-magnet placed above York's 

 instrument. The armature is attracted, and frees the detent of the alarum, 

 setting it ringing until York signals ready. London then stops the bell, 

 and commences his message. By following the direction of the current, 



FIC.-4. 



Fig. 253. Passage of the current (2). 



when the handle is turned to the left, as in fig. 4, it will be readily seen how 

 this is effected : commencing with London's copper, LC, it passes up before 

 and down behind London's needle, flowing along the wire between the two 

 cities to York's needle, up before and down behind which it travels, sending 

 it also to the left. It then passes to York's right plate, through the 

 connector to the left plate, and so on to earth at York, coming to the 

 surface again at London, passing through London's right plate and through 

 the lower part of the handle to the zinc of the battery. The reverse 

 current may be easily followed. Any number of instruments with similar 

 needles may be interposed along the course of the wire. When the operator 

 wishes to speak to any particular one, he rings all the bells for attention, 

 and then signals Derby or Nottingham, as the case may be. They all then 

 throw their instruments out of current except the one required. The mode 

 by which the needle movements are converted into language is simple. 

 A is signalled by causing the needle to vibrate once to the right, B once 

 right and once. left, C once right and twice left ; and so on, as arranged, 



