ELECTRIC OSCILLATIONS AND ELECTRIC WAVES. 233 



everywhere be opposite in sign, that is, wherever the one is 

 positive the other must be negative. Thus the projections upon 

 the plane of the paper of the numbered arrows in Fig. 1 70 repre- 

 sent the instantaneous values at the various points of a trans- 

 mission line of the alternating currents i which are associated 



transmission line 



direction of progression > 



^ ; 



of wave-train 



direction of 

 clock-diagram rotation 



helix 



side view of clock-diagram model en d view of model 



Fig. 170. 

 Clock diagram model of a simple wave train moving to the left. 



with a simple wave train moving from right to left, and the 

 projections of the lettered arrows represent the instantaneous 

 values of the alternating voltage e. 



126. Clock diagram model of a standing wave train. When 

 a string vibrates as a whole or in segments, the mode of motion 

 of the string constitutes what is called a standing wave train, 

 and in a simple standing wave train every particle of the string 

 performs simple harmonic motion of the same frequency and of 

 the same (or opposite) phase. The amplitude of the motion 

 varies from zero at the nodes to a maximum at the antinodes. 

 A clear idea of the mode of motion of such a string may be 



