96 SCIENCE REMAKING THE WORLD 



toward the negative electrode. Both may produce 

 further ions from the normal molecules of gas with 

 which they collide if the impacts are sufficiently violent. 



Such, in general, is the phenomenon of conduction 

 through gases. In solid bodies, like wires, conduction 

 occurs by the motion of free electrons which wander this 

 way and that through the intermolecular or interatomic 

 spaces. The metals, the best conductors, are electro- 

 positive, that is, their atoms are systems with incon- 

 venient electrons in excess of the simplest configura- 

 tional requirement but not in excess of the number of 

 protons in the atoms. It is these loosely held electrons, 

 most probably, which serve to conduct electricity 

 through solid conductors. Their haphazard wander- 

 ings are superseded by a definite drift when the ter- 

 minals of the solid are connected to a battery. 



This phenomenon of electron streams in wires con- 

 ducting electricity is made to furnish the electrons 

 which form the stream through the vacuum of an 

 audion. The audion consists of an evacuated vessel 

 with a filament through which a current of electricity 

 may be passed. There is also a metal plate and be- 

 tween the plate and the filament a fine wire-grid. 



A strong current of electricity through the filament is 

 manifested by its rise in temperature and its lumines- 

 cence. Both the heat and the light are due to the dis- 

 turbances created among the atoms of the wire by the 

 stream of electrons which constitutes the current. The 

 individual electrons of the stream, which is being forced 

 through the filament by an external battery, must dodge 

 or jostle their way past the more fixed atomic systems 



