CONTENTS OF VOL. XLII. FIFTH SERIES. Vll 



NUMBEE CCLIX.— DECEMBER. 



Prof. R. Threlfall and Mr. J. A. Pollock on some Experiments 



with Rontgen's Eadiation 453 



Dr. C. Davison on the Diurnal Periodicity of Earthquakes . . 463 

 Mr. W. Sutherland on Thermal Transpiration and Radio- 



meter Motion 476 



Lord Eayleigh on Theoretical Considerations respecting the 



Separation of Gases by Diffusion and similar Processes . . 493 



Dr. Gr. J. Stoney on Microscopic Vision 499 



Notices respecting New Books : — 



J. H. Tan 't Hoffs Studies in Chemical Dynamics 528 



On Experiments with Eontgen Rays, by Prof. Augusto Eighi. 530 

 Volume Measurement of an Air-Thermometer Bulb, by 



Walter G. Cady 530 



On the Influence of Temperature on the Eefraction of Light 



by Metals, by C. Piilfrich 532 



Index 533 



PLATES. 



I. & II. Illustrative of Prof. A. W. Witkowski's Paper on the Thermo- 

 dynamic Properties of Air. 



III. to V. Illustrative of Messrs. Frith and Rodgers's Paper on the 

 Resistance of the Electric Arc. 



