KONINKLIJKE AKADEMIE VAN WETENSCHAPPEN 

 TE AMSTERDAM. 



PROCEEDINGS OF THE MEETING 



of Saturday September 25, 1915. 



Vol. XVIII. 



President: Prof. H. A. Lorentz. 

 Secretary: Prof, P. Zeeman. 



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

 Natuurkundige Afdeeling van Zaterdag 25 September 1915, Dl. XXIV). 



CONTENTS. 



P. Zeeman : "On the passage of light through the slit of a spectroscope", p. 412. 



Q. A. F. MOLENORAAFF: "On the occurrence of nodules of manganese in mesozoic deep-sea deposits 



from Borneo, Timor, and Rotti, their significance and mode of formation", p. 415. (With one plate). 

 Jan DE VRIES: "Bilinear congruences of twisted curves, which are determined by nets of cubic 



surfaces ', p. 431. 

 Chs. H. van OS: "Associated points with respect to a complex of quadrics". (Communicated by Prof. 



Jan de VrieS', p. 441. 

 F. E. C. SCHEFFER: "On the allotropy of the ammonium halides" 1. (Communicated by Prof. A. F. 



HOLLEMAN), p. 446. 

 H. Kamerlinqh Onnes, C. Dorsman and O. Holst : "Isothermals of di-atomic substances and their 



binary mixtures. XVll. Preliminary measurements concerning the isothermal of hydrogen at 



20° C. from 60 to 90 atmospheres", p. 458. 

 H. Kamerlinqh Onnes, C. A. Crommelen and Miss E. 1. Smid; "Isothermals of di-atomic substances 



and their binary mixtures. XVlll. The isothermal of hydrogen at 20' C. from 60— 100 atmospheres", 



p. 465. 

 C. A. Crommelin and Miss E. I. Smid: "Comparison of a pressure-balance of SCHaFFER and 



BUDENBERQ with the open standard-gauge of the Leiden Physical Laboratory between 20 and 



100 atmospheres, as a contribution to the theory of the pressure-balance". (Communicated by 



Prof. H. KAMERLINQH ONNES i, p. 472. (With one plate). 

 W. H. Keesom and H. Kamerlinqh ONNES : "Thespecificheatatlowtemperatures.il. Measurements 



on the specific heat of copper between 14 and 90° K.", p. 4iM. 

 H. Kamerlingh Onnes and Sophus Weber : "Further experiments with liquid helium. O. On the 



measurement of very low temperatures. XXV. The determination of the temperatures which 



are obtained with liquid helium, especially in connection with measurements of the vapour- 

 pressure of helium", p. 493. 

 H. Kamerlinqh Onnes : "Methods and apparatus used in the cryogenic laboratory. XVI. The 



neon-cycle", p. 507. 

 H. Kamerlinqh Onnes and C. A. Crommelin: "Isothermals of monatomic gases and of their 



binary mixtures. XVII. Isothermals of neon and preliminary determinations concerning the 



liquid condition of neon", p. 515. 

 S. H. Koorders: "Sloanea javanica (Miqueli Sszyszylowicz, a remarkable tree growing wild in the 



jungle of Depok, which is maintained as a nature reserve'. iContribution to the Flora of Java, 



part Villi. (Communicated by Prof. M. W. Beijerinck), p. 521. 

 F. A. F. C. Went and A. A. L. RUTGERS: "On the influence of external conditions on the flowering 



of Dendrobinm crumenattim Lindl", p. 526. 

 F. A. H. SchreinemakerS: "In-, mono- and divariant equilibria" II, p. 531. 

 H. Haqa and F. M. JAEOER: On the Symmetry of the RöNTQEN-patterns of Trigonal and Hexagonal 



Crystals, and on Normal and Abnormal Diffraction-Images of birefringent Crystals in general", 



p. 542. (With 7 plates). 

 H. HAQA and F. M. JAEQER: "On the Symmetry of the RoNTOEN-patterns of Rhombic Crystals". I, 



p. 559. iWith 4 platesi. 

 K. Kuiper Jr. "The Physiology of the Air-bladder of Fishes". III. (Communicated by Prof. MAX WEBERl, 



p. 572. 

 Erratum, p. 582. 



27 



Proceedings Royal Acad. Amsterdam. Vol. XVIII. 



