﻿Electric Waves obtained by Valves. 



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expand?, the spring prevents sagging. Surrounding the 

 filament is a cylindrical wire grid, GG, composed of thin 

 wire of square mesh, each square having a side of about 

 1*5 mm. The lead to the grid goes out at the bottom near 

 the filament leads. A cylindrical plate, PP, surrounds the 

 whole with its lead going out through the top of the bulb. 

 These valves being used for transmitting purposes are very 

 thoroughly "glowed out * and pumped to a very high vacuum. 

 The filament emission is very high when heated with 6 volts 

 direct, and for the low emissions that were generally used it 

 was very constant. As the plate lead passes through the top 

 of the bulb, instead of through the bottom and the sealed 



Fisr. 1. 



socket, very high insulation is obtained, and, if a strip of 

 tinfoil connected to earth is placed round the outside of the 

 gla-s, very small anode currents may be measured by an 

 electrometer without any disturbance due to leakage. 



It is not necessary for ordinary wireless purposes that the 

 valves should be constructed with the grid and plates either 

 accurately circular in section or accurately centred with 

 regard to the filament ; but for the purpose of calculation a 

 svmmetrical system of electrodes is necessary and the M.T.5 

 valve used in most of the experiments was specially selected. 

 All the numerical results to be quoted were obtained from 

 this valve. There is no difficulty in getting the short-wave 

 oscillations with many types of hard valve, the French type 

 produces them quite easily, but the chief reason for selecting 

 the Marconi M.T.5 type was that the electrostatic field 

 between the square-mesh grid and the plate approximates 



M2 



