KONINKLIJKE AKADEMIE VAN WETENSCHAPPEN 
TE AMSTERDAM. 
PROCEEDINGS 
VOLUME XVIII 
N°. 8. 
President: Prof. H. A. LORENTZ. 
Secretary: Prof. P. ZEEMAN. 
(Translated from: Verslag van de gewone vergadering der Wis- en 
Natuurkundige Afdeeling, DI. XXIV). 
CONTENTS. 
J. J. VAN LAAR: “On the Additivity of the Values of 6 and Wa of the Equation of State, and on 
the Fundamental Values of these Quantities for Different Elements, in Connection with the 
Periodic System”, (Communicated by Prof. H. A. LORENTZ), p. 1220. 
J. J. VAN LAAR: “On the Validity of MATHEWS’ so-called Valency Law”, (Communicated by Prof. 
H. A. LORENTZ), p. 1235. 
P. ZEEMAN: “An optical method for determining the ratio between the mean and maximal velocities 
in the turbulent motion of fluids in a cylindrical tube. Contribution to the experiment of 
FIZEAU”, p. 1240. 
W. H. KEESOM and H. KAMERLINGH ONNES: “The specific heat at low temperatures. III. Measure- 
ments of the specific heat of solid nitrogen between 14° K. and the triple point and of liquid 
nitrogen between the triple point and the boiling point” (Communicated by Prof. H. KAMER- 
LINGH ONNES), p. 1247. 
J. F. VAN BEMMELEN: “On the phylogenetic significance of the Wing-markings in Hepialids”, p. 1255. 
I. K. A. WERTHEIM SALOMONSON: “Resistance, Polarisation and the Psycho-galvanic Reflex”, p. 1266. 
JAN DE VRIES: “Characteristic numbers for nets of algebraic surfaces”, p. 1270. 
JAN DE VRIES: “Tangential curves of a pencil of rational cubics”, p. 1277. 
W. J. DE HAAS: “Further experiments on the moment of momentum existing ina magnet”. (Commu- 
nicated by Prof. H. A. LORENTZ), p. 1281. 
G. J. ELIAS: “On the influence of alternating currents of decreasing intensity on the magnetisation 
of iron.” (Communicated by Prof. H. A. LORENTZ), p. 1299. 
T. VAN LOHUIZEN: “On the ratio between the ZEEMAN-effect and the pressure-effect in the spectrum 
of nickel.” (Communicated by Prof. P. ZEEMAN), p. 1309. 
J. D. VAN DER WAALS JR. and Miss AUDA SNETHLAGE: “The Theory of the BROWN’ian Movement.” 
(Communicated by Prof. J. D. VAN DER WAALS), p. 1322. 
A. SMITS: “The P,X-figures of Unary Systems, according to the Theory of Allotropy.” (Communicated 
by Prof. J. D. VAN DER WAALS), p. 1334. 
H. HAGA and F. M. JAEGER: “The Symmetry of the Rontgen-patterns of Tetragonal Crystals”, p. 1350. 
(With four plates). 
F. M. JAEGER and H. HAGA: “On Röntgen-patterns of Isomorphous Crystals” p, 1357. (With four 
plates). 
C. OTTO ROELOFS: “On the function of the m. obliquus superior of the eye.” (Communicated by 
Prof. G. VAN RIJNBERK), p. 1364. 
A. H. W. ATEN: “On Cathode Scattering in Electrolysis”. (Communicated by Prof. A.F. HOLLEMAN), 
p. 1374. 
F. A. H. SCHREINEMAKERS: “In-, mono- and divariant equilibria” VII, p. 1384. 
C. WINKLER: “On the brains of cyclops and monstra related to them”, p. 1399. 
Proceedings Royal Acad. Amsterdam. Vol. XVIII. 
