XX CONTENTS 
Physics. J. Droste: “On the field of two spherical fixed centres in ErNsTEiN’s theory 
of gravitation”. 760. 
— G Horsr: “On the measurement of very low temperatures”. XXVI. 829. 
— J. EB. VerscuarreLT: “The viscosity of liquefied gases’. [. 840. II. 860. ILI. 
1028. IV. 1659. 
— W. H. Kexsom: “Two theorems concerning the second virial coefficient for rigid 
spherical molecules which besides collisional forces only exert CouLoms-forces and 
for which the total charge of the active agent is zero”. 868. 
— G. Horsr and L. Hampurcer: “Investigation of the equilibrium liquid-vapour 
of the system argon-nitrogen”. 872. 
— fF. ZerNiKe: “An interpolation-formula for resistance-thermometry at low 
temperatures”. 914. 
— L. H. Stertsrma: “The magnetic rotation of the plane of polarisation in titane 
tetrachloride”. IL. 925. 
— O. Postma: ‘Entropy and probability”. 1048. : 
— G. J. Erras: “On the reversible change of the remanent magnetisation with the 
temperature’. 1068. 
— Miss H. J. van LEEUWEN: “Some remarks on the hydrogen-molecule of Bour- 
DeBye”, 1071, 
— H. Haca and F. M. Jancer: “The symmetry of the Röntgen-patterns of 
monoclinic erystals”. 1201. 
J. J. vaN Laar: “On the additivity of the values of 6 and Wa of the equation 
of state, and on the fundamental values of these quantities for different elements, 
in connection with the periodical system”. 1220. 
— J. J. van Laar: “On the validity of MatnEws’ so-called valency-law’. 1235. 
— P. Zeeman: “An optical method for determining the ratio between the mean 
and maximal velocities in the turbulent motion of fluids in a eylindrical tube. 
Contribution to the experiment of Fizgav”. 1240. 
— W. H. Kersom and H. KAMERLINGH Onnes: ‘“The specific heat at low temperatures 
III. Measurements of the specific heat of solid nitrogen between 14° K. and the triple 
point and of liquid nitrogen between the triple point and the boiling point”. 1247. 
— W. J. pp Haas: “Further experiments on the moment of momentum existing 
in a magnet”. 1281. 
— G. Js Extas: “On the influence of alternating currents of decreasing intensity 
on the magnetisation of iron”. 1299. 
—— T. van Lonurzen: “On the ratio between the Zepman-elfect and the pressure- 
effect in the spectrum of nickel”. 1509. 
— J. D. van per Waats Jr. and Miss Aupa SNETHLAGE: “The theory of the Brownian 
movement”. 1322. 
— H. Haca and F, M. Jararr: “The symmetry of the Röntgen-patterns of tetra- 
gonal crystals”. 1350. 
— Miss A. SNETHLAGE: “On the BrowNian movement in gases’. 1480. 
— F. Zeuke: “The clustering-tendency of the molecules in the critical state 
and the extinction of light caused thereby”. 1520. 
