CHAFFEE. — IMPACT EXCITATION OF ELECTRIC OSCILLATIONS. 307 



although the damping is linear, the separate oscillation loops are 

 distorted as will appear presently. 



Cut d of Plate 6 represents the condition when the discharge ter- 

 minals of the secondary gap are carbon. The discharge was quiet and 

 very brilliant, resembling, as indeed it was, the pure carbon arc operat- 

 ing, however, at a frequency of 5.7 X 10^ oscillations per second. 



Figure 18. Form of Spark Gap Damping Curve. 



Cut e of Plate 6 gives the appearance of the oscillogram when the 

 terminals are of aluminum in air. The discharge in this case, as well 

 as for cuts b and c, was probably a pure arc due to the carbon and 

 other impurities in the aluminum. In appearance, the discharge was 

 brilliant and similar to the carbon arc. 



Magnesium terminals usually give the pure-arc discharge-form of 

 damping curve, due probably to the large amount of magnesium vapor 

 present in the discharge, or possibly to the burning of the magnesium 

 into the oxide. 



Cut/ of Plate 6 and the pictures of Plate 7 represent the appearance 

 of the spark discharge oscillograms. When the temperature of the 



