ELECTRIC OSCILLATIONS AND ELECTRIC WAVES. 207 



The plus sign relates to a wave moving to the right in Fig. 140, 

 and the negative sign relates to a wave moving to the left in 

 Fig. 140. 



A clear understanding of an electric wave traveling along a 

 transmission line may be obtained from Fig. 141, resistance of 



current 



current 



Fig. 141. 

 Showing an electromagnetic wave on a transmission line. 



line wires being negligible and wires being perfectly insulated. 

 The curve WW corresponds to CC in Fig. 140, and the ordi- 

 nate y represents the voltage e across the line or the current i 

 in the line at the point p. The upper wire is positively charged 

 and the fine vertical lines represent the lines of force of the electric 

 field which emanates from the positively charged wire and con- 

 verges upon the lower wire in the figure which is negatively 

 charged. Current flows to the right in the upper wire and to the 

 Jeft in the lower wire as represented by the short horizontal 

 arrows, and the fine dots represent the lines of force of the mag- 

 netic field between the wires, this magnetic field being perpen- 

 dicular to the plane of the paper in Fig. 141. The heavy arrow 

 V shows the direction of travel of the wave. 



The direction of travel and the directions of e and i may be 

 correlated as follows: That particular wire is positively charged 

 out of which the electric lines of force emanate; the voltage e is 



