596 Hon. E.J. Strutt on the Electrical 



ideal gas, defined as one in which the aggregate mass and 

 aggregate energy of the molecules remain constant through- 

 out any possible natural motion, and which is such that the 

 physical state of the gas is fully defined by its density and 

 temperature, this steady state is given by the well-known 

 Boltzmann law. These results depend upon the " molekular- 

 ungeordnet " assumption, but are not limited by the hypo- 

 thesis of binary encounters. 



If the Boltzmann law does not give the steady state there 

 must be some other variables besides the density and tempe- 

 rature, a knowledge of which is necessary to determine the 

 physical properties of a sample of gas. 



A gas in nature can never attain a steady state on account 

 of the interaction between matter and aether. I have tried to 

 follow out some of the consequences of this in former 

 papers *. 



In a future paper I hope to apply the methods of the 

 present paper to some problems of dissociation and ionization. 



LXVI. The Electrical Conductivity of Metals and their Vapours. 

 By the Hon. R. J. Strutt, Fellow of Trinity College, 

 Cambridge^. 



i 



§ 1. Introduction. 



T is known that mercury vapour, even at very high tem- 

 peratures, is a good insulator ; a better one in fact than 

 air under similar conditions J. Liquid mercury, on the other 

 hand, is of course a good conductor, like other metals. Let 

 us try to form some idea of what the difference in conductivity 

 between the liquid and the saturated vapour amounts to. 



1 1 is stated in the paper referred to that mercury vapour 

 at atmospheric pressure, even at a yellow heat, allowed a much 

 smaller current to pass than air under similar conditions. With 

 air, contained in a tube 7x1 inches, into which the electrodes 

 dipped, a current was observed which was measured by ten 

 scale-divisions on a sensitive galvanometer, when an E.M.F. 

 of 156 volts was applied. We may suppose that one scale- 

 division represented a current of not more than 10 — 9 amperes, 

 and that the mercury vapour gave only I the current 

 observed with air. Thus the current would be 2 x 10~ 9 amp. 



* " The Distribution of Molecular Energy," Phil. Trans, cxcvi. p. 397 ; 

 " The Mechanism of Radiation," Phil. Mas. [6] ii. p. 421 ; " The Theo- 

 retical Evolution of y," Phil. Mag. [6] ii. p." 638. 



t Communicated "bv the Author. 



X J. J. Thomson, Phil. Mag. [5] xxix. p. 364. 





