Discharge of Electricity through Argon and Helium. 293 



in general too high, and the resistivity formula too low a value 

 for the conductivity. 



The conductivity of a mixture appears not to be dependent 

 solely on the volume and conductivity of each constituent 

 present. 



The empirical formula (4) gives a fair representation of 

 the observations in the preceding tables. 



XXIV. On the Discharge of Electricity through Argon and 

 Helium. By Hon. R. J. Strutt, B.A., Scholar of 

 Trinity College, Cambridge*. 



IN" this paper I propose to describe some observations, 

 partly quantitative and partly qualitative, on electrical 

 conduction through these gases. The observations include 

 measurements of the fall of potential over the negative glow 

 in a vacuum-tube, observations on the luminous effects pro- 

 duced by the discharge, and comparisons of the rate at which 

 ions are produced in them and in air, under the influence of 

 Rontgen rays. 



The argon was produced from atmospheric air, the nitrogen 

 being removed by sparking with oxygen in presence of caustic 

 alkali. The surplus oxygen was removed with phosphorus. 

 The helium was extracted from Brazilian monazite-sand by 

 boiling it with sulphuric acid. It was purified in the same 

 way as the argon. 



The gases were introduced into the discharge-tubes by the 

 method described by Prof. W. Ramsay (Trans. Chem. Soc. 

 v. 1895, p. 686). 



Measurements of the Cathode-Fall of Potential. 



The investigations of Hittorf and Warburg have shown 

 that when a steady current passes through a gas the differ- 

 ence of potential between the cathode and the outside of the 

 negative glow is a constant, independent of the current 

 passing through the gas, and of the pressure, provided that — 



(a) There is no chemical action between the cathode 

 and the gas ; 



[b) That the negative glow does not cover the whole 

 of the cathode, and is not interfered with by the walls of 

 the tube. 



This constant potential-difference is known as the cathode- 

 fall. It is usually of the order of 300 volts, and has a different 

 value for each gas. So far as I am aware, no relation has 



* Communicated by the Author. 

 Phil. Mag. S. 5. Vol. 49. No. 298. March 1900. X 



