KONINKLIJKE AKADEMIE VAN WETENSCHAPrEN 

 TE AMSTERDAM. 



PROCEEDINGS OF THE MEETING 

 of Saturday October 28, 1905. 



(Translated from; Verslag van de gewone vergadering der Wis- en Natuurkundige 

 Afdeeling van Zaterdag 28 October 1905, Dl. XIV). 



co3srTEi<ra?s. 



H. DE Vries: "Central Projection in the space of LoBATsciiEFSKY",(lst Part). (Communicated 

 by Prof. J. Cardinaal), p. 389. 



H. J. Hamburger: "A method for determining the osmotic pressure of very small quantities 

 of liquid ', p. 394. 



EuGEN Fischer: "On the primordial cranium of Tarsius spectrum". (Communicated by Prof. 

 A. A. W. Hubrecht), p. 397. 



H. A. LoRENTZ: "On the radiation of heat in a system of bodies having a uniform tem- 

 perature", p. 401. 



H. Zwaardemaker: "On the ability of distinguishing intensities of tones. Keport of a research 

 made by A. Deenik", p. •121. 



Erratum, p. 426. 



The following papers were read : 



Mathematics. — ''Central Projection 171 the space of Lobatsvuefsky" . 

 (i^f part). By Prof. H. de Vkies. (Communicated by Prof. J. 

 Cardinaal). 



(Communicated in the meeting of September 30, 1905). 



1. Let an arbitrary plane r be given in hyperbolic space; let 



the perpendicular be erected in an arbitrary point Oj of r, and let 



finally an arbitrary point be taken on this perpendicular. We can 



now ask what we can notice if we project the figures of space 



out of as a centre of projection on t as a plane of projection or 



picture plane, and inversely, how the exact position and situation of 



the figures in space can be determined by means of their projections. 



27 

 Proceedings Royal Acad. Amsterdam. Vol. VllI, 



