ELECTRIC OSCILLATIONS AND ELECTRIC WAVES. 221 



might produce a troublesome tidal wash in a large estuary while 

 the attempt was being made to "open-circuit" the estuary in 

 this Brobdignagian fashion! Let the reader consider this 

 hydraulic analog carefully. It reproduces nearly all of the es- 

 sentials of the electrical case. The conducting vapor in the arc 

 of a circuit breaker is somewhat analogous to mud as a dam 

 building material. 



Very little need be said of characteristic line surges in connec- 

 tion with opening of switches, except in the case of very long lines. 

 When a line is short, or only moderately long, what takes place 

 may be described quite accurately in terms of the simple ideas 

 of the elementary alternating-current theory, where current values 

 are supposed to rise and fall simultaneously throughout an entire 



/~-large inductance 

 / _ wire 



wire 



000000 



D 

 QQQQQO wire wire 



Fig. 158. 



The dotted line AB represents the initial current in the transmission line. The 

 long heavy arrow with laps represents the ribbon wave which comes from D after 

 the line at D is opened. 



circuit. The formation of a long arc between line wires in air 

 and the quick snapping out of such an arc does, however, produce 

 an electric wave disturbance on a transmission line of moderate 

 length, and the essential features of this case are shown in Fig. 

 158. Imagine the system to be short-circuited by an arc at the 

 distant end D of the transmission line, voltage being reduced to a 



