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



in the filament, but the current from the filament varied 

 with the grid voltage. For the lower voltages all the 

 electrons leaving the filament do not r^ach the grid space, 

 some returning to the filament. For theoretical reasons it is 

 more convenient to find the grid voltages which give the 

 maximum amplitudes of oscillation on the various wave- 

 lengths when the heating current is so adjusted that the 

 same current flows from the filament to the grid space for all 

 the voltages, the plate voltage being kept constant as before. 

 The table below gives a set of experiments done under such 

 conditions with an emission current of 6 milliamperes, and 

 the plate at 1'3 volts positive to the filament. In column 1 

 are given the wave-lengths \ in cms., in column 2 the grid 

 volts V, which excite these wave-lengths most strongly, and 

 in column 3 the product X 2 V: — 



X. 



V. 



X 2 Y. 



208 cm. 



156-5 



68xl0 5 



233 



122-5 



66 



262 



92-5 



64 



307 



68-5 ' 



64-5 



366 



505 



67-5 



451 



36-5 



74 



All these results, with the exception of the last, agree well 

 with the relation X, 2 Y = const. 



It is not difficult to see why this agreement should be less 

 exact as V decreases. The electrons concerned are not all 

 moving under similar conditions. Owing to the voltage drop 

 of the heating current down the filament, the field between 

 filament and grid differs by about 4 volts for electrons starting 

 from the extreme ends of the filament. And when V be- 

 comes comparable to this 4 volts a disturbing factor is 

 introduced. 



6. These experiments thus give the grid voltages which 

 produce the strongest oscillations on certain definite wave- 

 lengths determined by the particular length of wire used. 



To find the range of wave-lengths maintained by a given 

 grid voltage a slightly different apparatus (fig. 4) was used. 

 An adjustable circuit was constructed of two rods, and two 

 telescopic tubes fitted over the rods, so that the effective 

 lengths of the system could be varied by sliding the tubes 

 over the rods* 



The condensers and thermo-jnnctions were attached at the 

 endsX, X 1 of the rods, and the ends Y, Y 1 of the tubes were 

 connected to the plate and grid of the valve respectively, the 

 other connexions being as before. 



