270 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



Part I. 



The General Characteristics of the Oscillation Gap. 



(1) Description of Apparatus. 



The gap consists essentially of an aluminum cathode and an anode 

 of some other metal such as copper or silver, both water or air cooled 

 and surrounded by an atmosphere of moist hydrogen. The active sur- 

 faces of the terminals are accurately parallel planes of one or two 

 square centimeters area, and adjustable as to distance separating 



Figure 1. Air-cooled Cu-Al Discharge Gap. ^ natural size. 



them, which, for the best results, is about .07 mm. Large terminals 

 are undesirable on account of the increased electrostatic capacity of 

 the gap, which must be small in comparison with the main capacity of 

 the circuit. 



For the cathode, aluminum is the only metal which gives at all satis- 

 factory results, and the gap should be constructed so that the termi- 

 nals can be occasionally renewed. After the gap has been in operation 

 for some time the aluminum becomes pitted and covered with a very 

 hard oxide which is difficult to remove. One electrode was operated, 



