﻿6t6 Prof. 0. W. Richardson : Some Applications 



virtue of electric and thermal conduction and thermionic 

 emission. The result of that investigation may be summa- 

 rized in the statement that at any point inside the enclosure 

 where the time average of the potential energy of an electron 

 is ft) and the time average of the number of electrons per c.c. 

 is n, then 



R01ogn + « = C (49) 



C is constant at every point inside the enclosure but may 

 be a function of temperature. In general there will be a 

 steady average field of electric force inside the enclosure 

 dependent upon the natural contact difference of potential. of 

 the enclosed bodies. Thus n will vary from point to point 

 of the space of the enclosure as well as in the interior of the 

 material bodies. 



Now electronic emission is not the only means of inter- 

 change of energy and electric charge between bodies not in 

 contact which is universally operative. To it we must cer- 

 tainly add electromagnetic radiation and in all probability 

 photoelectric action as universal properties of matter. It 

 may seem strange to those unfamiliar with the phenomena, 

 thus to postulate the universality of electronic emission. A 

 little consideration, however, will show that in its relations 

 to matter and to temperature, electronic emission is in pre- 

 cisely the same general position as electromagnetic "sethereal" 

 radiation. All bodies radiate sethereally in a perceptible 

 manner at high temperatures just as all bodies, being con- 

 ductors of electricity, emit electrons under similar conditions. 

 At ordinary temperatures most, but not all, bodies cease to 

 emit electrons in measurable quantity just as many trans- 

 parent bodies cease to emit sethereal radiation in measurable 

 quantity. The difference in this respect is exaggerated by 

 the more rapid temperature variation of the electronic as 

 compared with the sethereal emission. The really important 

 difference is that the electronic radiation is affected by a 

 field of electric force, whereas the sethereal radiation is not. 

 This causes the electronic radiation from an isolated body 

 very rapidly to become infinitely slow, whereas there is no 

 such effect on the sethereal radiation. 



In general, then, we have to consider interchanges to be 

 taking place by virtue of conduction, electronic emission, 

 sethereal radiation, and photoelectric action. Any perfectly 

 reflecting enclosure containing real bodies in thermal equi- 

 librium will be filled with sethereal radiation which will give 

 rise to photoelectric emission. The enclosure will, therefore, 

 contain an atmosphere of electrons even when the materials 

 have no thermionic emissivity ; if we keep the term thermionic 



