CHAFFEE. — IMPACT EXCITATION OF ELECTRIC OSCILLATIONS. 275 



been gradually shifted over to Ci as ii decreased toward zero. The 

 main current /„ flows into Ci at a practically constant rate, neutraliz- 

 ing the inverse charge and charging it in the initial direction. The 

 potential difference of Ci increases uniformly, attaining a much higher 

 value than exists outside the choke coils. 



Impressed across the gap is the potential difference of the condenser 

 Ci plus the ripples induced in the primary circuit by the secondary 

 current, these potential ripples serving as a trigger to start the primary 

 discharge on a second cycle in the proper phase relation with the 

 secondary oscillation. 



It is evident from the above consideration that, on account of the 

 inductances Lg Lg, the condenser Ci can attain a much higher differ- 

 ence of potential than that of the source, the magnitude of this 

 condenser potential being determined by the breaking-down potential 

 of the gap. It is also clear that, if this breaking-down potential be 

 assumed approximately constant, the number of discharges of Ci per 

 second depends upon the main current 7^. 



The duration of each primary discharge does not, as has been stated, 

 depend upon the supply current, so that it is only the duration of the 

 interval between primary discharges which changes with varying main 

 current. The secondary continues to oscillate during these intervals 

 with decreasing amplitude according to the damping of the secondary 

 circuit. In what follows the number of secondary oscillations to one 

 primary discharge and charge is spoken of as the " inverse charge 

 frequency referred to the secondary oscillation " or simply I. C. F. 



From what has been said it is clear that the secondary receives 

 periodic impulses from the primary, the frequency of these impulses 

 depending upon the main current and the capacity of the primary 

 condenser. During the intervals of non-activity of the primary circuit 

 the secondary circuit oscillates in its own free period and with damping 

 determined solely by the conditions of the secondary circuit, such as 

 resistance and radiation. The secondary oscillation cannot, then, 

 strictly be called undamped. The amplitude of the oscillation can, 

 however, be maintained practically constant by making the primary 

 impulses occur every two or three secondary oscillations, and, if the 

 damping in the secondary circuit be small, the resulting oscillations are 

 then almost perfectly undamped and continuous. 



In order that the maximum energy be transferred to the secondary 

 circuit there are two conditions of syntony, as they may be termed, 

 to be fulfilled. In the first place the primary discharges must always 

 occur in the proper phase relation with the secondary oscillation, or, 

 in other words, the I. C. F. must be a whole number. This is, as has 



