Physics. — “Space-time-symmetry. Ill. Remarks on the deduction 
of groups of space-time symmetry-operations.” By N. H. Kork- 
MEIJER. Communication N°. 7c from the Laboratory of Physics 
and Physical Chemistry of the Veterinary College at Utrecht. 
(Communicated on behalf of Prof. W. H. Krersom, Director of 
the Laboratory, by Prof. H. KAMERLINGH ONNES.) 
(Communicated at the meeting of January 29, 1921). 
§ 1. Zntroduction. In Comm. N°. 7a’) the s.-t.-symmetry opera- 
tions have been derived, Comm. N°. 75%) gave examples of the 
application of these on a couple of models. With the purpose to 
start the study of the s.-t.-symmetrical atom models I have spent 
some time with finding out all groups of s.-t.-symmetry operations 
that are connected with point groups. The results of this investiga- 
tion would take too much space here. Therefore only a few remarks 
follow on the way of deduction of the groups in question. 
As moving particles we shall choose one atom nucleus and a 
finite number of electrons, all without dimensions. 
§ 2. Possibility of the existence of the s.-t.-symmetrical atom models. 
In the first place we may prove in a way analogous to that followed 
by Lanpé®) in the discussion of the possibility of his models, that the 
s.-t.-symmetrical atom models are consistent with the action of the 
forces. | 
In the second place: Among the models found in the way here 
indicated there will be some that do not satisfy the demand, (Comm. 
N°. 76%), for an atom model, that the configuration of nucleus and 
electrons returns periodically. This is f.i. the case with all models in 
which we have to do with one retroduction only. We might call 
them quasi atom models. For the sake of a systematic treatment 
we shall have to consider these too. 
In the next § we shall see, that it is impossible that to the ope- 
1) These Proceedings, p. 1419. 
3) These Proceedings, p. 1428. 
5) A. LANDÉ, Verh. d. D. Physik. Ges. 21, p. 2, 1919. 
“yale: 
