﻿170 Messrs. E. W. B. Gill and J. H. Morrell on Short 



The effect of: (A) varying the emission current keeping 

 the grid and plate voltages constant, and (B) varying the 

 plate voltage keeping the emission current and potential 

 between grid and plate constant was investigated with this 

 apparatus. 



In (A) increased emission broadened the range and de- 

 creased the wave-length of maximum oscillation. 



For example, with V^ p = 44 volts and ~V p f—l'2 volts the 

 wave-length for best oscillation with total emission 7*0 m.a. 

 was 295 cm. With total emission 10'6 m.a. it was 274 cm. 



In (B) increase of plate voltage increased the wave-length 

 and also broadened the range. Thus with Y^ = 44 volts, 

 and total emission 3*8 m.a. with Y p f=l'2 volts X = 298 cm., 

 and for V^ = 3*0 volts \ = 321 cm. This last observation 

 must not be confused with the case in which the potential of 

 the plate is increased and that of the grid kept constant. In 

 that case also, increase of plate potential increases the length 

 of the strongest wave, as was observed by Barkhausen, who 

 attributed all the difference in wave-length to the alteration 

 in potential difference between plate and grid. This cannot 

 be the whole of the explanation, for, as stated above, similar 

 results may be obtained by raising both plate and grid 

 equally with respect to the filament. 



7. A simple theory to account for the maintenance of the 

 oscillations can be worked out by making some simplifying 

 assumptions ; but a general theory will not be attempted, 

 partly because the resistance of the oscillating circuits used 

 was unknown and partly because if the assumptions are not 

 made the calculations become extremely complicated. 



These assumptions are : — 



A. That the grid and plate can be regarded as forming a 



parallel plate condenser. 



B. That, of the electrons which leave the filament, a fixed 



small proportion pass through the grid in a uniform 

 stream, and that each electron on passing through the 

 grid has the same velocity. 



C. That the electrons which return to the grid from the 



plate side are nearly all collected directly on it, i. e., 

 only a few pass through on the return journey. 



D. That the oscillating potential differences are small com- 



pared with the fixed potential differences employed. 



It is also assumed that the pressure of the gas inside the 

 valve is so low that the number of collisions between electrons 

 and gas molecules is negligible — this is certainly true for the 

 valves used. 



