KONINKLIJKE AKADEMIE VAN WETENSCHAPPEN 



TE AMSTERDAM. 



PROCEEDINGS 



VOLUME XXV 

 NOS. 3 and 4. 



President: Prof. F. A. F. C. WENT. 

 Secretary : Prof. L. BOLK. 



(Translated from : "Verslag van de gewone vergaderingen der Wis- en 

 Natuurkundige Afdeeling," Vol. XXXI). 



CONTENTS. 



H. J. VAN VEEN: "Axes of Rotation of Quadratic Surfaces tfirough 4 Given Points". (Communicated 



by Prof. Jan de Vries), p. 52. 

 H. J. VAN VEEN: "Axes of Rotation and Planes of Symmetry of Quadratic Surfaces of Revolution 



through 5, 6 and 7 Given Points". (Communicated by Prof. jAN DE Vries), p. 61. 

 P. Zeeman and H. W. J. Dik: "A Connection between the Spectra of Ionized Potassium and Argon". 



(First Communication), p. 67. 

 J. W. N. Le HeuX: "Explanation of some Interference-Curves of Uni-axial and Bi-axial Crystals by 



Superposition of Elleptic Pencils". (Third paper). (Communicated by Prof. Hendrik de Vries), 



p. 81. (with one plate). 

 ). W. Janzen and L K. WOLFF: "Studies on the bacteriophagus of d'Herelle", If (Communicated 



by Prof. C. EVKMAN), p. 87. 

 G. HERTZ: "On the Mean Free Path of Slow Electrons in Neon and Argon", (Communicated by 



by Prof. P. Ehrenfest), p. 90. 

 G. J. VAN Oordt: "On the morphology of the testis of Rana fusca Rösel". (Communicated by Prof. 



J. BOEKE), p. 99. 

 G. SCHAAKE: "A New Method for the Solution of the Problem of the Characteristics in the 



Enumerative Geometry". (Communicated by Prof. HENDRIK DE VRIES), p. 113. 

 W. H. KEESOM and J. DE Smedt: "On the diffraction of Rontgen-rays in liquids". (Communicated 



by Prof. H. Kamerlingh Onnes), p. 118. (With one plate.) 

 N. H. KOLKMEijER: "The crystal structure of germanium". (Communicated by Prof. H. Kamerlingh 



Onnes), p. 125. 

 R. J. WOLVIUS: "An Objective Method for determining the Co-agulation-time of Blood". iCommuni- 



cated by Prof. A. A. Hijmans van den Bergh), p. 127. 

 *F. J. J. BUYTENDIJK: "A Contribution to the physiology of the electrical organ of Torpedo" 



(Communicated by Prof. Q. VAN RljNBERK), p. 131. 

 Rudolph J. hamburger: "On the Significance of Calcium- and Potassium-ions for the artificial 



Oedema and for the lumen of the bloodvessels". (Communicated by Prof. H. J. Hamburger), 



p. 145. 

 Erratum, p. 150. 



Proceedings Royal Acad. Amsterdam. Vol. XXV. 



