( 148 ) 



êveiy horizontal layci- correspoiids ajiollier density accordiiig- to the 

 formula of hydrostatics: 



dp = — Q(id/t. 



For temperatures far below the critical one this circiimslance is 

 of little importance; for the critical temperature itself, however, the 

 influence of gravity is considerable. If we write namely the formula 

 of hydrostatics in the following form : 



1 dp dh 



Q dQ ' dQ 



dp dh 



then we see that — = or — = x at that poiiil of the height ot the 

 dQ dQ 



do 

 vessel w'here the critical j)hase really occui-s, i. e. where — = 0. 



dh 



If therefore we c(»iisti'iict a graphical representalion of the successive 



densities, laying out the height as abscissa and the density as the 



ordinate, then we get a continually descending curve. In the beginning 



its concave side is turned downwards ; at a certain point the tangent 



is vertical and the ciir\e has a point of iidhwioii ; farllier the convex 



side is turned downwards. In the neiglibouriiood of the critical 



phase we find therefore a rapid change in the density. 



The equation of state can only account for the state of ('qf////hri//ti) 

 described above as it deals only with states of equilibrium. Another 

 question is how tliat equilibriiun is established and whether it is 

 established in a longer or shorter time according to the method of 

 investigation. 



It has been observed several times in these latter years that the 

 state of equilibrium of a quantity of a substance which is contained 

 in a closed vessel slowly heated to the ci'itical temperature, requires 

 so long a time before it has been reached that some iiivestigators have 

 concluded that the liqiud consists of other molecules than the va])Our. 

 De Heen, Galitzine, Traube and others speak therefore of "molecules 

 liquidogènes" and "molecules gasogènes". Some of them suppose the 

 "molecules liquidogènes" to be more complex, others suppose them 

 to be only smaller. This latter supposition agrees with the ideas 

 I have expressed in my "The ec^uation of state and the theory of 

 cyclic motions." And for aii explanation of the fact that the equi- 

 librium is so slowly established, these investigators refer to the slow 

 diffusion of the heterogeneous molecules. 



To this fact they refer however wrongly. The kinetic theory 

 accounts satisfactorily for the slowness of the diffusion and has even 

 enabled us to calculate the coefficient of diffusion for mixtures of 



