KONINKLIJKE AKADEMIE VAN WETENSCHAPPEN 
TE AMSTERDAM. 
ime CEE DINGS 
VOLUME XXII 
N°. 6. 
President: Prof. H. A. LORENTZ. 
Secretary: Prof. P. ZEEMAN. 
(Translated from: “Verslag van de gewone vergaderingen der Wis- en 
Natuurkundige Afdeeling,” Vol. XXVII and XXVIII). 
CONTENTS, 
JAN DE VRIES: “On an involution among the rays of space”, p. 478. 
JAN DE VRIES: “On an involution among the rays of space, which is determined by two REYE 
congruences”, p. 482. 
G. SCHAAKE: “On an involution among the rays of space”. (Communicated by Prof. JAN DE VRIES), 
p. 488. é 
JAN DE VRIES: “On an involution among the rays of space, which is determined by a bilinear 
congruence of twisted elliptical quartics”, p. 493. 
A. W. K. DE JONG: “The trimorphism of allocinnamic acid”. (Communicated by Prof. P. VAN 
ROMBURGH), p. 497. 
A. W. K. DE JONG: “The Truxillic Acids”. (Communicated by Prof. P. VAN ROMBURGH), p. 509. 
P. ZEEMAN and Miss A. SNETHLAGE: “The Propagation of Light in Moving, Transparent, Solid 
Substances. Il. Measurements on the FIZEAU-Effect in Quartz”, p. 512. (With one plate). 
M. J. SMIT: “On some nitro-derivatives of dimethylaniline”. (Communicated by Prof. P. VAN 
ROMBURGH), p. 523. 
P. H. J. HOENEN S. J.: “Pressure- and temperature-coefficients, volume- and heat-effects in bivariant 
systems”. (Communicated by Prof. F. A. H. SCHREINEMAKERS), p. 526. 
P. H. J. HOENEN S. J.: “Extension of the law of Braun”. (Communicated by Prof. F. A. H. SCHREI- 
NEMAKERS), p. 531. 
D. COSTER: “On the rings of connecting-electrons in BRAGG’s model of the diamondcrystal” (Com- 
municated by Prof. H. A. LORENTZ), p. 536. 
F. A. H. SCHREINEMAKERS: “In-, mono- and divariant equilibria’, XX, p. 542. 
W. KAPTEYN: “On a formula of SYLVESTER”, p. 555. 
A. J. P. VAN DEN BROEK: “About the influence of radio-active elements on the development”. 
Communicated by Prof. H. ZWAARDEMAKER), p. 563. (With one plate), 
B. VON KeréwjartTé: “Ueber die endlichen topologischen Gruppen der Kugelfliche’. (Communi- 
cated by Prof. L. E. J. BROUWER), p. 568. 
NIL RATAN DHAR: “Catalysis. Part. VII. Notes on Catalysis in heterogeneous systems”. (Com- 
municated by Prof. ERNST COHEN), p. 570. 
NiL RATAN DHAR: “Notes on Cobaltammines”. (Communicated by Prof. ERNST COHEN), p. 576, 
C. H. VAN OS: “An involution of pairs of points and an involution of pairs of rays in space”. 
(Communicated by Prof. JAN DE VRIES), p. 580. 
J. A. SCHOUTEN and D. J. STRUIK: “On n-tuple orthogonal systems of n—I-dimensional manifolds 
in a general manifold of n dimensions”. (Communicated by Prof, J. CARDINAAL), p. 504, 
L. RUTTEN: “On Foraminifera-bearing Rocks from the Basin of the Lorentz River (Southwest 
Dutch New-Guinea)”, p. 606. 
H. GROOT: “On the Effective Temperature of the Sun” (2nd Communication). (Communicated 
by Prof. H. W. JULIUS), p. 615, 
C. B. Biezeno: “Graphical determination of the moments of transition of an elastically supported, 
statically undeterminate beam”. 1. (Communicated by Prof, J. CARDINAAL), p. 621. 
Proceedings Royal Acad. Amsterdam. Vol. X XI 
