KONINKLIJKE AKADEMIE VAN WETENSCHAPPEN 
TE AMSTERDAM. 
PROCEEDINGS 
VOLUME XIX 
N°. 8. 
President: Prof. H. A. LORENTZ. 
Secretary: Prof. P. ZEEMAN. 
(Translated from: “Verslag van de gewone vergaderingen der Wis- en 
Natuurkundige Afdeeling,” Vol. XXV). 
CONTENTS. 
W. REINDERS and L. HAMBURGER: “Ultramicroscopic investigation of very thin metal- and saltfilms 
obtained by evaporation in high vacuum”. (Communicated by Prof. J]. BOESEKEN), p. 958. 
A. D. FOKKER: “The virtual displacements of the electromagnetic and of the gravitational field in 
applications of HAMILTON’s variation principle.” (Communicated by Prof. H. A. LORENTZ), p. 968. 
J. D. VAN DER WAALS Jr.: “On the Energy and the Radius of the Electron”. (Communicated by 
J. D. vAN DER WAALS), p. 985. 
H. I. WATERMAN: “Amygdalin as nutriment for spergillus niger.” IL. (Communicated by Prof. J. 
BOESEKEN), p. 987. 
H. J. HAMBURGER and R. BRINKMAN: “Experimental researches on the permeability of the kidneys 
to glucose. I. The proportion between K and Ca in the circulating fluid”, p. 989. 
H. J. HAMBURGER and R. BRINKMAN: “Ibid. Il. The potassium required in the circulating-fluid is 
replaced by Uranium and Radium.”, p. 997. 
F. A. H. SCHREINEMAKERS: “In-, mono- and divariant equilibria”. XV, p. 999. 
Miss A. SNETHLAGE: “Experimental Inquiry into the Laws of the Brownian Movement in a Gas”, 
(Communicated by Prof. P. ZEEMAN), p. 1006. 
H. R. KRUYT: “Current Potentials of Electrolyte solutions”. (Second communication), (Communicated 
by Prof. ERNST COHEN’. p. 1021. 
S. DE BOER: “Contribution to the knowledge of the influence of digitalis on the frog's heart. Sponta- 
neous and experimental variations of the rhythm”. (Communicated by Prof. G. VAN RIJNBERK). 1029. 
H. ZWAARDEMAKER.: “On the Analogy between Potassium and Uranium when acting separately in 
contradistinction to their antagonism when acting simultaneously”, p. 1043. 
H. KAMERLINGH ONNES: “Methods and apparatus used in the cryogenic laboratory. XVII. Cryostat 
for temperatures between 27° K. and 55° K.”, p. 1049. 
H. KAMERLINGH ONNES, C. A. CROMMELIN and P. G. CATH: “Isothermals of mon-atomic substances 
and their binary mixtures. XVIII. A preliminary determination of the critical point of neon”. 
(Communicated by Prof. H. KAMERLINGH ONNES), p. 1058. 
J. E. VERSCHAFFELT: “The viscosity of liquefied gases. VI. Observations on the torsional oscillatory 
movement of a sphere in a viscous liquid with finite angles of deviation and application of 
the results obtained to the determination of viscosities”. (Communicated by Prof. H. KAMERLINGH 
ONNES), p. 1062. : 
J. E. VERSCHAFFELT: “The viscosity of liquefied gases. VII. The torsional oscillatory motion of a 
body of revolution in a viscous liquid’ (Communicated by Prof. H. KAMERLINGH ONNES), p. 1073. 
J. E. VERSCHAFFELT: “The viscosity of liquefied gases. VIII. The similarity in the oscillatory rotation 
of es of revolution in a viscous liquid”. (Communicated by Prof. H. KAMERLINGH ONNES), 
p. 1079. 
J. E. VERSCHAFFELT and CH. NICAISE: “The viscosity of liquefied gases IX. Preliminary determi- 
nation of the viscosity of liquid hydrogen’. (Communicated by Prof. H. KAMERLINGH ONNES), 
. 1084. 
Je PP KUENEN and A L. CLARK: “Critical point, critical phenomena and a few condensation-constants 
of air”, p. 1088. 
J. D. JANSEN: “On the distinction between methylated nitro-anilines and their nitrosamines b 
means of refractometric determinations.” (II). (Communicated by Prof. ERNST COHEN), p. | 
H. B. A. BOCKWINKEL : “Some Considerations on Complete Transmutation.” (Second communication). 
(Communicated by Prof. L. E. J. BROUWER), p. 1100. : 
J. WOLFF: “On the nodal-curve of an algebraic surface.” (Communicated by Prof. HK. DE VRIES). 
p. . . . . 8 ” 
C. E. DROOGLEEVER FORTUYN—VAN LEYDEN: “On an eel, having its left eye in the lower jaw”. 
(Communicated by Prof. J. BOEKE), p. 1120. 
Proceedings Royal Acad. Amsterdam. Vol. XIX. 
