CH. XIII] 



CURRENT RECTIFIERS 



493 



especially when used with moving picture projection. When 25 

 cycle current is used directly (is used raw) to supply the arc, the 

 result is very bad. The screen shows a violent flicker. The 

 general appearance is much the same as when a pan of mercury is 

 jarred rapidly, the surface appears covered with ripples. This 

 effect is naturally very trying to the eyes. 



FlG. 262. OSCILLOGRAMS OF THE ALTERNATING CURRENT SUPPLY AND THE 

 DIRECT CURRENT DELIVERED. 



(Cut loaned by the General Electric Co.; made from the original photograph'). 



Curve A The direct current delivered. 

 B The direct current zero line. 

 C The alternating current voltage curve and its corresponding zero 



line. 



The height of the curve A above its zero line B represents the instantaneous 

 value of the direct current. Note that while there are slight fluctuations in the 

 current, i. e., it is slightly pulsating, the current is always in the same direction 

 and that these fluctuations amount to only about 30% of the average value. 

 Note also that the maximum current value corresponds to a maximum positive 

 value or to a maximum negative value of the alternating current voltage as 

 shown in curve C given just below. 



