246 



PLEASANT WAYS IN SCIENCE. 



ously returned to the reservoir at the other; but it could 

 equally be carried through a pipe extending from that reser- 

 voir to some place where it could communicate with the 

 open sea the reservoir itself communicating with the open 

 sea an arrangement corresponding to that by which the 

 return wire is dispensed with, and the current from the wire 

 received into the earth. 



The discovery that the return wire may be dispensed 

 with was made by Steinheil in 1837. 



The actual arrangement, then, is in essentials that repre- 

 sented in Fig. 4. 



FIG. 4. 



A and B are the two stations ; P N is the battery at A, p' N' 

 the battery at B ; p' p' are the positive poles, N' N', the negative 

 poles. At n is the needle of station A, at n' the needle of 

 station B. When the handle of the commutator is in its 

 mean position which is supposed to be the case at station 

 B the points b 1 d' are connected with each other, but 

 neither with a' nor c' no current, then, passes from B to A, 

 but station B is in a condition to receive messages. (If b' 

 and d' were not connected, of course no messages could be 

 received, since the current from A would be stopped at b' 

 which does not mean that it would pass round ' to b\ but 

 that, the passage being stopped at b', the current would not 

 flow at all.) When (the commutator at B being in its mean 

 position, or d' b' connected, and communication with c 1 and 

 a! interrupted) the handle of the commutator at A is turned 



