158 PHYSICAL SCIENCE 



fraction of the current might pass through the 

 space surrounding the wire, which must become 

 filled with electrons. Although in gases at 

 ordinary pressures the emission of electrons is 

 less copious, still, ionization will occur to an 

 appreciable extent just round the wire, and a part, 

 though perhaps a small part, of the current will 

 pass along outside the substance of the wire. 



The phenomena we are now considering have 

 a practical application in the art of wireless tele- 

 graphy and telephony (see Chapter VIII.). But 

 they also have an important bearing on cosmical 

 processes. The photosphere of the sun contains 

 large quantities of glowing carbon, and this carbon 

 will emit electrons until the resultant positive 

 charge left on the sun exerts an electro-static 

 force great enough to prevent further emission. 

 In this way a condition of equilibrium would be 

 reached. Any local elevation of temperature 

 would then cause a stream of electrons to leave 

 the sun and pass into the surrounding space. 

 When electrons pass through a gas with high 

 velocity, they make it luminous, and Arrhenius 

 and others have explained many of the periodic 

 peculiarities of the Aurora Borealis by the 

 supposition that electrons from the sun, due 

 either to incandescence or to some other cause, 

 stream through the upper regions of the earth's 

 atmosphere. 



The phenomena of electrolytic conduction 

 through liquids, and of non-electrolytic conduction 

 through metallic substances, must now be inter- 

 preted in terms of this electronic theory. The 

 chemical decomposition of electrolytic solutions, 



