30 



THE ELECTRIC TELEGRAPH. 



arrangement for bringing two points alternately in commu- 

 nication with two others. Let a and c, Fig. 14, be two 

 points in connection with the two poles of a battery, or other 

 electromotive system, and b and d the ends of any other 

 circuit ; if the metal bars e and/ be pressed upon the ends 

 a b and c d respectively, the current will pass in the direc- 



Fig. 14. 



tion B -f- a e b R df c B. But if the bars e and f be 

 removed from these positions and placed at right angles, 

 that is to say, e between b and c, and /between a and d, as 

 shown by the dotted lines, the current will go through 

 B -f- d R (in the opposite direction) b c B. 



On lifting up the coil a a, Fig. 12, from the stool to the 

 top of the vertical magnet-bars, a current was induced in 

 the wire encircling them. This current passed by the com- 

 mutator, placed as in Fig. 14, from a to b, through one of 

 the line wires and the multiplier R of the receiving station, 

 deflecting the magnet for an instant in one direction, and 

 returned by the other wire over c and d of the commutator. 

 When it was wished to deflect the needle of the receiving 

 instrument in the opposite direction, this was attained by 

 simply lowering the coil a a again to its original place, and 

 the observer at the receiving station read off one deflection 

 to the right, for instance, and one to the left. But, in con- 

 structing a code of signals, it was necessary that two or 

 more deflections to the right or left should frequently follow 

 each other. This was done by means of the commutator. 



