Royal Academy of Sciences. Amsterdam, 



]'R0Cr]EDIKG8 OF THE MEETING 

 of Saturday May 28th i898. 



(Translated from: Verslag van tie gewone vergadering der Wis- en Naliiurlcundigc 

 Afdecling van Zaterdaa; 28 Mei 1898 1)1. VII). 



Contests: „On the cyclographic space representation of Joachimsthal's circles". By Prof. 

 P. H. ScHOUTE, p. 1. — „On maxima and minima of apparent brightness resulting 

 from optical illusion". By Dr. C II. Wind (cummunieated by I'rof. II. IIaga) with 1 

 plate, p. 7. — «On the relation of the obligatous anaërobics to free oxygen". By 

 Prof. M. W. Beijerinck, p. 14. — „On the inHnenoe of solutions of salts on the volume 

 of animalcells, being at the same time a contribution to our knowledge of their struc- 

 ture". By Dr. H. J. Hamburger; p. 26. — „On an asymmetry in the change of 

 the spaetral lines of iron, radiating in a magnetic held". By Dr. P. Zee.mak, p. 27. — 

 „The Ilall-etlect in electrolytes". By Dr. E. van Everdingen Jr. (communicated by 

 I'rof H. Kamerlingh Onnes) p. 27. 



The following papers were read : 



Mathematics. — „On the cijdoyruijkic space j-cprescutution ofjud- 

 chimdhcd's circles.''' By Prof. P. II. Schoute. 



1. Ill his „Cyklographie" Dr. W. Fiedler has developed a 

 theory, in which any circle of the plane is represented in space by 

 one of two points of the normal, erected in its centre on the plane, 

 and having on either side a distance from this centre equal to the 

 radius. The ambiguity of this representation can be useful in the 

 distinction of the two senses, in which a point can move along the 

 circle. This is not necessary here. 



According to the Fiedlerian representation the right cone, whose 

 vertex is a point P of the plane of the circles, whose axis is the 

 normal in P on this plane, and whose vertex angle is a right one, 

 corresponds to the net of the circles passing through P. Likewise 

 the pencil of the circles passing through P and Q has as image a 

 rectangular hyperbola situated in the plane bisecting P Q orthogo- 



1 



Proccediugs Royal Acad. Amsterdam. Vol. I. 



