22 



ELEMENTS OF ELECTRICAL ENGINEERING. 



arrow, a large current enters the wire at a y part of this current 

 goes to charge the wire positively, and the current decreases in 

 value towards c ; and the current which enters the alternator at 

 b does not flow all the way around from a but part of it comes 

 from the wire and leaves the wire negatively charged. The action 

 is analogous in every detail to the action which takes place in 

 Fig. 21. 



In Fig. 19 the only appreciably elastic element is the dia- 

 phragm DD, whereas in Fig. 21 the entire circuit of pipe is 

 elastic. In Fig. 20 the only place where an appreciable amount 



robber tube 



wire 



A 



wire 



Fig. 22. 



of electric charge accumulates is on the two metal plates CC, 

 the amount of charge that accumulates on the wire being negli- 

 gible. In Fig. 22 the amount of charge that accumulates on the 

 wire is supposed to be appreciable ; this is true only when the 

 circuit of wire is very long, as in a long transmission line, and in 

 this case an appreciable charge accumulates all along the wires. 

 The metal plates in Fig. 20 constitute what is called a concen- 

 trated capacity, and the wire in Fig. 22 constitutes what is called 

 a distributed capacity. 



The effects of distributed capacity are exceedingly complicated 

 and they are always ignored in ordinary alternating-current prob- 



