CHAFFEE. — IMPACT EXCITATION OF ELECTRIC OSCILLATIONS. 303 



current. During the discharge the potential of the primary condenser 

 falls and increases in the opposite direction, so that, at the end of the 

 discharge, represented at C, the condenser potential is reversed. At 

 point C the primary discharge is completed. The rest of the diagram 

 from C to A is due to the secondary oscillation, which causes the 

 vertical deflection, and the uniformly changing potential of the primary 

 condenser while charging, which causes the horizontal deflection from 



Cto^. 



The numher of secondary oscillations taking place during one pri- 

 mary cycle, and which has been called the I. C. F., is clearly shown by 

 the photographs. In the case of cut h, the secondary completes one 

 period during the primary discharge, and three complete secondary 

 periods during charging from G to A, so that the I. C. P. is 4. 



The instant at which the primary discharge begins and ends with 

 reference to the secondary wave, is shown to be the same as was 

 derived in the section on the primary wave. The high harmonic 

 oscillations in the primary which occur, as has been mentioned, after 

 the high resistance of the gap is broken down, are apparent in the 

 beaded appearance of the upper loops of the oscillograms. 



In cuts a-e of Plate 4 the spot travelled over the patterns in an anti- 

 clockwise direction. The I. C. P.'s are respectively 3, 4, and 6. In 

 cuts a and h the undeflected position of the spot is shown, and the 

 relative magnitudes of the direct and inverse potentials of the primary 

 condenser can be noted. 



The beats, shown in cuts c-f of Plate 4, are due to the interference 

 of two oscillations in a doubly-periodic secondary system employed in 

 this case. The second-secondary oscillation is due to the vibration 

 of an helix, a few turns of which were included in the secondary cir- 

 cuit. The luminous spot in cut d travelled in a clockwise direction. 



(5) Resistance Damping. 



In order to obtain an oscillogram of a variable which is a function 

 of time, it is necessary to use some device which will give a uniform 

 time axis to the figure. For instance, if it is desired to obtain an 

 oscillograph of the commercial alternating current, one passes the cur- 

 rent through the deflecting coil about the Braun tube. There appears 

 on the screen a straight line, which results from the to-and-fro move- 

 ments of the luminous spot over the same straight path. In order to 

 see the current wave developed with respect to time, it is necessary to 

 observe the line deflection in a revolving mirror, its axis being parallel 

 to the line deflection. If a photograph is to be taken, it is further 



