SO.UF. CO.MIi.UI'OR.IRy .IDl'.lXCrS IX rinsiCS C 645 



filled with litjuiil w.iitM or solid CiCOi. llir iiiii.iininK space inside 

 the chainhtT is quiikly pt-rvadi'd with HjO m ("(),; inoleciilcs conx- 

 posiiiK a gas, its pn-ssurc and doiisitN- luini; (IctiTniint'd ahsolutuly 

 l>y the temperature 7'. We infer thai if .m evacuated chamber, 

 with its walls made of some insulatinjj substance, contains a piece of 

 tnetal and is heated to a high temperature, the whole evacuated 

 space will be pervaded with electrons composing a gas, its pressure 

 /> and density w being determined absolutely by the temperature 

 of the system. T. We must assume that the electron-gas outside 

 the metal conforms to the ideal-gas law 



p = itkT (14) 



and we shall alsi) preseiilU .issiime that its specific heals have the 

 \alues characteristic of iimnainmic ideal gases, 



C,. = 'l.\h, C, = '!^Xk. (15) 



I use n to represent the luunber of electrons per unii xolume of tlu- 

 gas, as the number within the metal no longer enters in any way 

 into the reasoning; N to represent the number in a gramme-mole- 

 cule (Avogadro's constant). These are the only assumptions which 

 invoke a kinetic theory- in any way. 



Imagine now a wire of which one end projects into an evacuated 

 chamber of the sort described, maintained at T, and the other into 

 another such chamber maintained at T+dT. We consider a process 

 which consists of increasing the volume of the first chamber by just 

 enough to require A' additional electrons to come out of the wire 

 to till the additional space, and simultaneously decreasing the volume 

 of the second chamber by just enough to crowd A' electrons into 

 the wire; so that in effect A^ electrons are transferred from the one 

 chamber to the other through a wire of which the two ends are at 

 temperatures T+dT and 7". This process will be carried on re- 

 versibly. Designate by L the heat which must be imparted to the 

 metal at T, to remove one electron from it under the circumstances 

 of the experiment; by sdT the heat which is absorbed when one 

 electron is transferred through the metal from a point where the 

 temperature is T to a point where the temperature is T+dT. s is 

 the coetlicient of the Thomson effect, referred to a single electron 

 instead of a coulomb. L contains a term kT, which corresponds 

 to the mechanical work done in forcing back the walls of the chamber 

 to make place for the evaporated electron-gas. Subtracting it we 



