ARMSTRONG, OPERATING FEATURES OF THE AUDION 339 



insensitive to a further increase in the negative charge on the grid. The 

 strays which cause serious interference are of a much greater amplitude 

 than the local frequency, so that no appreciable interaction between the 

 two takes place, and the wing current is invariably decreased. Since the 

 decrease in the wing current is not in proportion to the change in the 

 grid potential, the response in the telephone and the effect on the ear of 

 the operator are correspondingly reduced. Static of smaller amplitude 

 than the local oscillations may interact with them to produce either an 

 increase or a decrease in amplitude of the oscillation in the grid circuit, 

 and may therefore cause either a decrease or an increase in the wing cur- 

 rent. The wing current can, of course, increase to a relatively large 

 value, but as it is impossible for the wing current to increase faster than 

 the charge in the grid condenser can leak off, the rate of increase is nec- 

 essarily slow. The response in the telephoaes is therefore not so dis- 

 turbing as would be caused by a decrease of similar value where the rate 

 of change of current is usually large. 



When the system is operated without an auxiliary leak around the 

 grid condenser, a peculiar paralysis of the audion is frequently caused 

 by heavy static, no sound of any kind being heard in the telephone for 

 a considerable length of time. If the apparatus is not touched, the 

 paralysis may last for many minutes, and then suddenly disappear and 

 the former sensitiveness be restored. The effect is primarily caused by 

 the charging of the grid condenser to a sufficient potential to cut off en- 

 tirely the flow of electrons to the wing, thereby decreasing the wing cur- 

 rent to zero. Now, the way in which the negative charge in the grid con- 

 denser leaks off is chiefly by means of the positive ions in the tube, which 

 are drawn into contact with the grid when it becomes negatively charged. 

 These positive ions are the result of ionization by impact, and when the 

 voltage of the wing battery is properly adjusted, they can be produced 

 only in the region between the grid and the wing, since the velocity at- 

 tained by the electrons between the filament and grid is very low. When 

 the grid is charged to a high negative potential it keeps all the electrons 

 between the grid and filament, thereby barring them, from the region be- 

 tween grid and wing. Hence the production of positive ions must cease, 

 and the usual means of removing the negative charge from the grid van- 

 ishes. The resistance of the leakage path of the grid condenser must 

 then be almost infinite, as is shown by the very long time taken for the 

 charge to leak from a condenser of approximately 0.0001 microfarads 

 capacity. The effect is naturally the more pronounced the higher the 

 vacuum, as the number of positive ions present is correspondingly re- 

 duced. A resistance of several hundred thousand ohms placed across the 



