1330 
4. From the preceding developments there is seen to be every 
reason for the expectation, that the development of the solution in 
powers of the excentricity of Titan, supposing the free libration of 
6 to be zero, will meet with no difficulties. This conelusion is at 
variance with Nrwcoms’s opinion in his paper: “On the motion of 
Hyperion. A new case in Celestial Mechanics’. There he reaches the 
conclusion, that the development in powers of e' is not possible. The 
incorrect performance of this development by Nerwcoms is the reason 
of this difference of opinion; he omits the terms in the differential 
eqnation, which arise from the part of the perturbative function 
that does not contain €; thus he gets a divisor of the order of m’ 
instead of one of the order of mm’. In this respect the theory of 
Hyperion appears to present no difficulty. 
In my dissertation I hope to extend the preceding developments 
by taking into account the amplitude of the free libration, as well 
as by giving more accurate results as regards the number of decimals. 
Chemistry. — “Vapour pressures in the system: carbon disulphide- 
methylaleohol”. By Dr. E. H. Bicuner and Dr. Aba Prins. 
(Communicated by Prof. A. F. HOLLEMAN). 
(Communicated in the meeting of March 31, 1917). 
With regard to the vapour of partially miscible liquids, we find 
in many textbooks the following consideration for the case that the 
composition of the vapour lies between that of the liquid phases. 
When, on altering the temperature, the concentrations of the two 
liquids tend to the same value and, finally, become identical in a 
critical solution point, the vapour also, it is argued, must have the 
same composition at that temperature. It is then, however, tacitly 
assumed that tie vapour, which lies at any low temperature between 
the liquids Z, and Z,, remains between them at all other tempera- 
tures. This is, however, not at all the case, as KUENEN *) already 
showed some years ago with the help of van DER Waats’ theory. In 
an analytical way he proved, on the contrary, that at the critical 
point the vapour must have a different composition. 
Also from general considerations it is easily seen that a vapour 
lying within the region of the two liquids must pass without, before 
the critical point is reached. If it did not, there would exist a point 
where three phases had the same composition. Now, it is already 
1) These Proc. 6, Oct. 1903. 
