534 



L.. Flamm ') has indicated iiow a space with that linear element 

 can be realized. The parabola situated in the .vz plane: 



z* = 4a(x — a) (2) 



has the linear element: 



dx 



ds = 



ly 



(3) 



] — 



If this parabola is rotated about the z axis, in the .ryz space, 

 there arises a rotation-surface with the linear element : 



dR' 

 +i?'rf^/' ...... . H) 



ds'=: 



a 

 R 



<p being the rotation-angle, measui'ed from the yz plane (fig. 1). 



Fig. 1. 



A fan of directions in the centre of the sun determines a system 

 of 00 ^ geodesic lines, together forming a diametral surface. Such 

 a diametral surface can as regards the parts beyond the surface of 

 the sun be developed on the rotation-surface (4) without changing 

 its linear element. R may approximately be equalized with the 



1) Beitrage zur Einstein'schen Gravitationslheorie 17 (16) 448—454. 



