416 Mr. 0. W. Eichardson. Electrical Conductivity [Feb. 28, 



On raising the temperature of the metal, the energy of the cor- 

 puscles is increased, and at high enough -temperatures some of them 

 will be able to shoot through the surface into the surrounding space. 



The number of corpuscles which escape at any temperature has; 

 been calculated on this view. The saturation current, which corre- 

 sponds to the number emitted per second, is given by the equation 



\2mn 

 where 



n is the number of free corpuscles in 1 c.c. of the metal, 

 e the charge on an ion, 



5 the area of the hot-metal surface, 



E the gas constant for a single corpuscle, whose mass is m, 



6 the absolute temperature, and 



3? the work done by an ion in passing through the surface layer. 



The rate at which energy is emitted, due to this cause, is also 

 calculated. 



Owing to the important part which the ionisation from hot bodies 

 has played in certain recent cosmological theories, the equations 

 which determine the equilibrium of corpuscles near a plane surface 

 of hot metal of infinite extent are also given and solved. 



The chief problem which has been attacked experimentally is the 

 way in which the saturation current from a negatively-charged hot 

 metal surface to a neighbouring electrode varies with the tempera- 

 ture of the metal. 



In the case of platinum, the hot metal consisted of a fine wire 

 spiral passing along the axis of a surrounding cylindrical electrode. 

 The temperature was obtained from the resistance of the wire. 



In the case of carbon, the leak was measured from a small lamp 

 filament to a surrounding cylinder. The temperature was estimated 

 in two ways : (1) by fastening a platinum and platino-iridium thermo- 

 couple of very fine wire round the filament, and (2) from the resistance 

 of the filament. 



With sodium this method could not be adopted. The metal was 

 distributed on the inner surface of a steel cylinder, and the current 

 from it to an insulated wire inside the cylinder was measured. The 

 temperature was obtained by a thermo-couple of copper and nickel. 

 Owing, doubtless, to the peculiar shape of the electrodes and the some- 

 what high pressure of the gas, the current with sodium was never 

 saturated. For this reason the current under a given voltage was 

 measured instead of the saturation current. 



Incidentally, it was found necessary to examine the relation between 

 the current and the applied electromotive force. Current E.M.F. 

 curves are given for all three substances, and, in the case of carbon,. 



