ELECTRIC OSCILLATIONS AND ELECTRIC WAVES. 235 



rods (arrows), one set of rods (or arrows) being in one plane and 

 the other set of rods (or arrows) being in a plane at right angles 

 thereto; the whole is supposed to be rotating at a speed of / 

 revolutions per second in a counter-clockwise direction as seen 

 from right hand end; and the projections of the arrows on the 

 plane of the paper represent the instantaneous values of current 

 and voltage at the various points of a transmission line which is 

 oscillating in a simple mode or on which there is a standing wave 

 train of electromagnetic waves. 



transmission line 



short-circuited 

 end 



advancing wave-train 

 (numbered vectors) 



direction of 

 clock-diagram rotation 



10 



reflected wave-train 

 (lettered vectors) 



side view end view 



Fig. 173. 



Clock diagram model of two simple wave trains, one moving to the right and 

 one moving to the left, 



The clock diagram model of Fig. 172 may be derived from Figs. 

 169 and 170 by considering that a standing wave train is the 

 superposition of two oppositely moving wave trains of equal 

 amplitudes. Let us consider the voltage distribution in a stand- 

 ing wave train with the help of Fig. 173 in which the numbered 

 arrows constitute the voltage helix from Fig. 169 (that is the 

 numbered arrows in Fig. 173 represent the voltages along the 



