1552 
Then we may say: the properties are valid, as long as the equi- 
libria 7), 47) and (#4) are situated within the turning-line of 
the field (FF, 
As in a P,7-diagram several fields are sitnated around the inva- 
tiant point, we have to take into consideration the turning-line of 
each field; then we may say: the properties are valid as long as 
we consider those parts of the curves and the fields, which are 
situated within the corresponding turning-lines. 
We have to bear in mind that “within the turning-line” means 
here “belonging to the same leaf on which the invariant point is 
situated”. 
The meaning of “not too far” and “not too much” in the con- 
ditions 1 and 2 is consequently indicated here somewhat more exactly, 
Above we have already stated that we may imagine that the 
€ 
phases of the ‘equilibrium (#, #,) satisfy reaction (3) casually in 
the invariant point; then the point 7 is situated in fig. 5 accidentally 
on the turning-line. Then the two curves (F) and (F,) come in 
contact with one another and with the turning-line in this point 7. 
The corresponding P,7-diagram forms then, as we have already 
mentioned, a transitiontype, to which we shall refer later. 
Leiden. Inorg. Chem. Lab. 
(To be continued). 
Physics. — “On the Symmetry of the Röntgen-patterns of Triclinic 
and some Rhombic Crystals, and some Remarks on the Diffrac- 
tion-Images of Quartz”. By Prof. Dr. H. Haca and Prof. 
Dr. F. M. JarGer. 
(Communicated in the meeting of March 25, 1916). 
$ 1. In the following paper we wish to communicate in the 
first place the results of the experiments, which as a sequel to 
our previous studies, were made with crystals of the ticlinic 
system. The erystals of each of the two symmetry-classes of this 
system: those of the ¢riclinic-pedial and those of the triclinic-pina- 
coidal class,—of which erystais the first mentioned are wholly wn- 
symmetrical, while the second possess only centrical symmetry,— 
will of course necessarily behave in the same way, as far as the 
diffraction-phenomenon of Röntgen-rays is concerned. But because 
the centre of symmetry cannot manifest itself in the structure of 
the Röntgen-images in any way, all obtained Röntgenogrammes will 
a 
