ELECTRONS 97 



and the stay-at-home electrons. They move with 

 considerable velocities and from time to time one is 

 diverted from the straight path of the conductor and 

 flies beyond the restricting influence of its protons to 

 the free space surrounding the filament. The number 

 that thus escape is very large, increasingly so at high 

 temperatures of the filament. 



Another battery is connected to the audion in such a 

 manner as to make the plate positive with respect to 

 the filament. The free electrons are then drawn across 

 the vacuum from filament to plate. On the way, how- 

 ever, they pass through the meshes of the grid. The 

 latter is strategically placed nearer the filament than 

 the plate. Feeble electrical changes in the condition 

 of the grid, therefore, produce pronounced changes in 

 the stream of electrons which flows from filament to 

 plate. Changes produced in this manner will be evi- 

 dent in the external portion of the electrical circuit 

 which is formed by the second battery, the filament, the 

 plate, and the intervening vacuum. The small inertia 

 of these individual electrons and the delicacy with 

 which the strategically placed grid controls their actions 

 have resulted in the marvellous application of the audion 

 to the electrical communication of speech by wire and 

 by radio. 



GUIDE TO FURTHER READING 



" Matter and Energy," by Frederick Soddy. (Henry Holt.) 1912. 

 ' nee and Life," by Frederick Soddy. (John Murray.) 1920. 

 "Within the Atom," by John Mills. (D. Van Nostrand and 

 Co.) 1922. 



