I28H . 



would have lo be applied lo the numerical factm- and use equation 

 (13) further uncorrected. 



l(n) -\ is the quantity that (tibbs represents hv (i and denotes 



A' / 



1»V the name of thermodynamic potential. In the case of thermo- 

 dynamic equilit>riuni it is constant, and equal to /{n^), when n^ is 

 the density in the point where the potential energy is put zero. In 

 the case of no eipiilibrium considered by us I shall put: 



/(n)+,4^-/0'.)=:'". (14) 



KJ 



or taking into account that we suppose lo lo be small: 



n =1 n^e ^'^' (\ -{- w) z= ti^e ^^ \ nw, .... (14a) 

 so that ////' represents the number of molecules that in consequence 

 of the current is present in an element of space in excess above the 



normal number n^e ^'^ . According to e(piation (J3) in is found as 

 the potential of imaginary agent, of which the density would 



l/3;r dn 

 be: — - — u . 

 a . nl ox 



To illustrate the meaning of the found formula we shall apply it 



for the following simple case: the field of forces arises from a single 



centre of forces, in which we lay the origin of the system of 



coordinates, the force l)eing only a function of r. If there was no 



current, this field of forces would in a gas give rise to a denser 



I'loud round (>, in which the density woidd only be a function of 



;■. Let us now think the gas set flowing with a conshnit velocity u 



in the negative .^-direction, and let us suppose this to bring about 



a filiriht variation in the density, so that by way of first approxi- 



bn 

 mation we raav take in equation (J3) the value of^— as it would 



ox 



be without current, hence : 



— =— n„f^ kl (15) 



bx " kTdx ^ ^ 



which causes equation (13) to become: 



|/3jr n de ,„ ^ 



V''^= i^'Ur"^ ^'^'"^ 



a .rd kl Ox 



The imaginary agent is then negative on the side of the positive 

 .j!-axis, and has an equal, but positive value on the side of the 

 negative .r-axis. Then the potential ir of this agent will be zero in 



