Physics. — Space-time-symmetry. Il. Discussion of a special case. 
The tetrahedrical atom-models of Lanpé”. By N. H. Kork- 
MEIJKR. Communicaton N°. 76 from the Laboratory of Physics 
and Physical Chemistry of the Veterinary College at Utrecht. 
(Communicated on behalf of Prof. W. H. Kegsom, Director of 
the Laboratory, by Prof. H. KAMERLINGH ONNrs). 
(Communicated at the meeting of January 29, 1921). 
§ 1. Introduction. Recently, Born, Lanpé and Mape.une *) (parti- 
ally in cooperation) have studied atom models in which the Beton 
circulating about the nucleus are distributed over a number of shells 
over each of which they are spread symmetrically. 
LANDÉ treats?) the problem of finding ‘orbits with polyhedrical 
symmetry” with the intention of reducing the p-bodies-problem of 
the p electrons (the nucleus is thought at rest) to a one-body-problem. 
A survey of the possibilities arising in this problem and an 
insight in the symmetry-character of the models in question can 
easily be obtained by considering the latter from the point of view 
of space-time-symmetry (denoted further on by s-t-symmetry) treated 
in a former communication ®). At the same time we may test in 
this way the usefulness of the considerations in question. We shall 
only consider the tetrahedrical models of LANDÉ. 
§ 2. 4 ie space group of SCHOENELIKS, on which the tetrahedrical | 
atom models of luANDÉ are based. In fig. 1 
the 24 points are indicated, that arise from 
the symmetry of the tetrahedrical group of the 
second kind Jy (hemimorphous hemihedry of 
the cubic system) of ScHOENFLIEs, when one 
of them is chosen arbitrarily *). SCHOENFLIES 
gives a summary of the non-aequivalent sy mme- 
try-operations of this group in the following way: 
1) See the papers cited in note 4 p. 1419. 
8) A. LANpÉ Verh. d. D. Phys. Ges. 21 (1919) p. 2, 644, 653, Zs. f. Physik 2 
(1920) p. 83. 
3) N. H. Kotkmever Comm. NO. 7a. These Proceedings p. 1419. 
4) The points at the other side of the sphere are denoted by thinner small circles. 
