CONTENTS XV 



Physics, p. Ehrenfest: "In what way does it become manifest in the fundamental 

 laws of physics that space has three dimensions?". 200. 



— W. J. H. Moll and L. S. Ornstein: "Contribulion to the research of liquid 

 crystals. IF. The influence of the temperature on the extinction; further experi- 

 ments upon the influence of the magnetic tield". 210. 



— J. E. Verschaffelt: "The equations of state of an associating^ substance". 865. 



— J. J. VAN Laar: "On the fundamental values of the quantities b and Va for 

 difterent elements, in connection with the periodic system". V. 492. VI. 505. 



— P. Zeeman: "Some experiments on gravitation. The ratio of mass to weight for 

 crystals and radioactive substances". 542. 



— H. C. BuRQER: "On the theory of the Brownian movement and the experiments 

 of Brillouin". 642. 



— P. Ehrenfest: "A paradox in the theory of the Brownian movement". 680. 



— Miss. H. J. FoLMER: "A new electrometer, specially arranged for radio-active 

 investigations". 684. 



— Miss. H, J, FoLMER and A. H. Blaauw : "Researches into the radio-activity of 

 the lake of Eookanje". 714. 



— J. J. van Laar: "On the course of the values of a and ^ for hydrogen at difl'erent 

 temperatures and volumes", 750. II. 1195. 



— J. E. Verschaffelt: "On the viscosity of liquefied gases". X. The viscosity of 

 liquid hydrogen". 986. 



— P. G. Cath and H. Kameelingh Onnes: "On the measurement of very low 

 temperatures. XXVII. Vapour-pressures of hydrogen etc.". 991. 1155. 



— W. H. Keesom and H. Kameelingh Onnes: "The specific heat at very low 

 temperatures. IV. Measurements of the specific heat of liquid hydrogen". 1000. 



— G. Holst and L. Hamburger: "On a method for determining spectral inten- 

 sities by means of photography". 1021. 



— G. Holst and A. N. Koopmans: "On the sparking-potential of argon-nitrogen 

 mixtures". 1025. 



— G. Holst and J. Scharp de Visser: " The brightness of the black body and 

 the mechanical equivalent of light". 1036. 



— L. Hambürgee: "On the light emission of gases and mixtures of gases by 

 electric discharges". 1043. 



— Mrs. T. Ehkenfest-Afanassjewa : "The definiten ess of macroscopic processes and 

 the kinetic theory". 1049. 



— G. Nordstrom: "On the mass of a material system according to the gravitation 

 theory of Einstein". 1076. 



— P. G. Cath and H. Kamerltngh Onnes : "Isothermals of monatoraic substances 

 and their binary mixtures". XIX. 1160. 



— P. G. Cath, H. Kamerlingh Onnes and J. M. Burgers :'*0n the measurement 

 of very low temperatures". XXVIII. 1163. 



— G. Nordstrom : "On the energy of the gravitation field in Einstein's theory". 1238. 



— J. D. VAN DER Waals Jr.; "On the theory of the Brownian movement". 1254. 



— W. J. de Haas: "On the diflraction phenomenon caused by a great number of 

 irregularly distributed apertures or opaque particles". 1278. 



