KONINKLIJKE AKADEMIE VAN WETENSCHAPPEN 
TH AMSTERDAM, 
PROCEEDINGS OF THE MEETING 
of Saturday January 27, 1900. 
2 
(Translated from: Verslag van de gewone vergadering der Wis- en Natuurkundige 
Afdeeling van Zaterdag 27 Januari 1900 Dl. VIII). 
Contents: “The determination of the Apex of the Solar motion”. By Prof. J. C. KAPTEYN, 
p. 353. — “On twisted quintics of genus unity”. By Prof. JAN Dr Vries, p. 374. — 
“The cooling of a current of gas by sudden change of pressure”. By Prof. J. D. van 
DER WAALS, p. 379. — “The direct deduction of the capillary constant ¢ as a surface 
tension”. By H. Hutsaor (Communicated by Prof. J. D. van per Waazs), p. 389. — 
“Determination of the latitude of Ambriz and of San Salvador (Portuguese West- 
Africa)”. By C. SANDERS (Communicated by Dr. E. F. van pe SANDE BAK- 
HUYZEN), p. 398. — “Methods and Apparatus used in the Cryogenic Laboratory. 
II. Mercury pump for compressing pure and costly gases under high pressure”, 
By Prof. H. KAMERLINGH ONNES, p. 406. — “Lipolytic ferment in human ascitic 
fluid’. By Dr. H. J. HAMBURGER, p. 406. — “The action of strong nitric acid upon 
the three isomeric chloro-benzoic acids and some of their derivatives. By Dr. P. J. 
MONTAGNE (Communicated by Prof. A. P. N. FRANCUIMONT), p. 407. — “The alleged 
identity of red and yellow mercure oxide” (II). By Dr. Eryst Conen (Communicated 
by Prof. H. W. Baxuuris RoozEBoom), p. 407. — “Determination of the decrease of 
the vapour tension of solutions by determining the rise of the boiling point”. By Dr. 
A. Suirs (Communicated by Prof. H. W. Bakuuis RoozEBoom), p. 407. — Erratum, p. 408. 
The following papers were read: 
Astronomy. — “The determination of the Apex of the Solar 
motion.” By Prof. J. C. KAPTEYN. 
1. Fundamental hypothesis. 
It is usually taken for granted that the best known determinations 
of the direction of the solar motion in space are based on the 
following hypothesis : 
Hypothesis H. The peculiar proper motions of the fixed stars 
have no preference for any particular direction. 
In reality however this is not quite correct; at a closer investi- 
26 
Proceedings Royal Acad. Amsterdam. Vol. II. 
