RECENT ADVANCES IN SCIENCE 559 



of studying the total emission of X-rays from certain metals 

 and of determining the range of validity of various theoretical 

 conclusions which state that the energy of emission of the 

 X-rays should be proportional to the atomic weight of the 

 radiating target and also to the square of the voltage between 

 the tube electrodes. The results only partly favour these 

 conclusions. Discrepancies appear generally at the critical 

 voltages for the characteristic radiations of the metal employed 

 as target. 



Of the theoretical papers published during the past few 

 months mention should be made of an investigation by Yohhio 

 Ishida (Phys. Rev. October) on the kinetic theory of a gas 

 consisting of monatomic molecules with no spherical symmetry 

 during its passage from a variable state to a condition of 

 statistical equilibrium. A paper by H. W. Nicholls on the 

 theory of electrical systems in which such elements as resist- 

 ance, inductance, and capacity vary according to some general 

 law will be found to be of interest by students of mathe- 

 matical physics (Phys. Rev. August). In the Proc. Roy. Soc. 

 December, and Phil. Mag. December, H. S. Allen discusses 

 various formulae connecting characteristic frequency and atomic 

 number. 



PHYSICAL CHEMISTRY. By Prof. W. C. McC. Lewis, M.A., D.Sc, 

 University, Liverpool. 



The Chemical Theory of Capillarity. — Since the time of Laplace 

 surface tension and capillary effects generally have been treated 

 from the purely physical standpoint. That is, forces of attrac- 

 tion are assumed between volume elements or molecules, the 

 forces being exerted in a uniform manner independent of the 

 direction. The molecule is regarded as a unit from the centre 

 of which the force emanates. The problem resolves into a cal- 

 culation of the magnitude of such forces expressed as a function 

 of the distance from their origin. The problem of the structure 

 of the interfacial layer separating two homogeneous phases, 

 such as liquid and vapour, has been investigated from this 

 point of view, and a certain amount of progress has been made. 

 The phenomenon of capillarity, however, is by no means well 

 understood. Treated in this manner, the subject becomes one 

 of very great complexity, the theoretical results in many cases 



