CHAFFEE. — IMPACT EXCITATION OF ELECTRIC OSCILLATIONS. 



299 



The change of resistance of the gap can be obtained experimentally 

 by use of a Braun tube provided with electrostatic deflecting plates. 

 These electrostatic plates are connected directly across the gap as 

 shown by Figure 17, causing a deflection perpendicular to that caused 



S60 



320 



280 



240 



.200 



160 



120 



80 



40 



AMPERES. 



Figure 16. Resistance Curves of Cu-Al Gap. 



G . . . . Glow Discharge. 

 L . . . . Discharge with Very Long Gap. 

 S . . . . Discharge with Very Short Gap. 

 Dotted curve .... Calculated. 



by the total current through the gap. In this way a trace of the 

 voltage-current characteristic curve is obtained from which can be 

 derived the resistance corresponding to any current. 



Cuts a-e of Plate 3 are photographs of E-I characteristic curves as 

 above described. Cut a represents the conditions for a very long gap. 

 The path of the spot of light, in tracing this figure, may be understood 

 from the following. As the condenser charges there is no current 



