CONTENTS XVII 



O N N E s (h. k a m e r l I n o h) presents a paper of Prof. J. E. Veeschaffelt : "On 

 tlie measurement of surface tensions by means of small drops or bubbles". 466 



— presents a paper of Prof. W. H. Keesom and Mrs. C. Norustuöm— van 

 Leeuwen : "Deduction of the third virial coefticient for material points (even- 

 tually for rigid spheres), which exert central forces on each other". -593. 



— presents a paper of Prof. W. H. Keesom and Mrs. C. Nordstrom — van Leeuwen : 

 ''Development of the third virial coefticient for material points (eventually rigid 

 spheres), which exert central attracting forces on each other proportional with 

 ?— 5 or;--6". 602. 



— presents a paper of Prof. J. E. Verschaffelt : "On the shape of large liquid 

 drops and gas-bubbles and the use made of them for the measurement of capil- 

 lary constants". 886. 



— presents a paper of A. J. Bijl and N. H. Kolkmeyer : "Investigation by means 

 of ^-rays of the crystalstructure of white and grey tin". I. 405. H. Tiie struc- 

 ture of white tin. 494. III. The structure of grey tin". 501. 



— presents a paper of Mr. P. G. Cath : "On the measurement of very low tem- 

 peratures. XXI -V. Vapour-pressures of oxygen and nitrogen for obtaining fixed 

 points on the temperature-scale below 0° C." 656. 



— presents a paper of L. Hamburger, G. Holst and E. Oosterhuis: "On the 

 influence of different substances on the absorption of light by thin tungsten 



layers". 1078. 



— presents a paper of G. Holst and A. N. Koopmans : "The ionisation of 



argon". 1089. 

 OÖGENESJS (Eflects of the Rays of Radium on the) of Daphnia pulex. 540. 

 oosterhuis (e.) and G. Holst. The audion as an amplifier. 932. 



— L. Hamburger and G. Holst. On the influence of difierent substances on the 

 absorption of light by thin tungsten layers. 1078. 



ophthalmoscope (A new). 937. 



optical behaviour (Experimental Inquiry into the Nature of the Surface-Layers in 

 the Refiection by Mercury, and into the Difference in the) of Liquid and Solid 

 Mercury. 678. 



ORBIT (The intermediary). Theory of .Jupiter's Satellites 1156, 



ORBITS (On the topographical relations of the) in infantile and adult skulls in man 

 and apes. 277. 



o R N s T E I N (l. 8.). The variability with time of the distributions of Emulsion- 

 particles. 92. 



— On the Brownian Motion. 96. 



— and H. C. Burger. On the theory of the Brownian motion. 922. 



— and W. J. H. Moll. Contributions to the study of liquid crystals. IIL Melting 

 and congelation-phenomena with para-azoxy-nuisol. 254. IV^ A thermic EÜ'ect of 

 the Magnetic Field. 259. 



— and F. Zernike. The Theory of the Brownian .Motion and Statistical Mechanic8.109. 



— and F. Zernike. The Scattering of Light by Irregular Refraction in the Sun. 115. 



— and F. Zernike. Magnetic properties of cubic lattices. 911. 



89 

 Proceedings Royal Acad. Amsterdam. Vol. XXI. 



