192 
oh tract more rapidly than the liquid- 
vapour surface, for this surface of 
nodes entirely disappears at the 
triple point temperature of BC. 
So if we draw the ternary critical 
BC end-point line in this case, we get 
a closed curve, as ‘is drawn in 
fig. 9 with a temperature mini-_ 
mum and maximum. 
A C If eritical end-points occur also 
Fig. 9. in one of the binary systems AB 
or AC or in both, other cases may occur, but they are easy to 
derive from what precedes. If also ternary compounds are included 
in our considerations, the cases get somewhat more complicated, as 
I hope to show on a following occasion. 
Anorg. chemical laboratory 
Amsterdam, June 27 1912. of the University. 
Astronomy. — “Researches on the orbit of the periodic comet 
Holmes and on the perturbations of its elliptic motion”. V. 
By Dr. H. J. Zwiers. (Communicated by Prof. EH. F. van DE 
SANDE BAKHUYZEN). 
In January 1906 I communicated to this Academy the most probable 
elements I had derived for the return of the comet Holmes in 1906— 
07. In a later paper, November 1906, I discussed the then known 
three photographic observations of the comet by Prof. Max Wo Lr 
at Heidelberg, and from these derived corrections to the mean longitude, 
to the inclination and to the longitude of the ascending node of the 
orbit. The elements obtained were: 
Epoch 1906 January 16.0 M. T. Greenw. 
M, = 351°47'36".838 
u = 517".447665 
log a = 0.5574268 
q 24°20'25".55 
D 20 49 0.62 
a=—=346 231.63, 1906.0 
S> = 331 4437 85 
These elements left the following errors O—C in the three observed 
places: 
