CONTENTS OF VOL. XXXVIII 



(SIXTH SE1UES). 



NUMBEK CCXXIII.-JULY 1919. 



■Page 

 Prof. W. M. Hicks on the Series System in the Spectrum 



of Gold 1 



Mr. W. -B. Hardy and Flight Lieutenant J. K. Hardy on 



Static Friction and on the Lubricating Properties of certain 



Chemical Substances :...,.... 32 



Mr. W. B. Hardy on the Spreading of Fluids on Glass .... 49 

 Prof. F. Allen on the Discovery of Four Transition Points 



in the Spectrum and the Primary Colour Sensations .... 55 

 Prof. F. Allen on the Persistence of Vision of Colours of 



Varying Intensity 81 



Dr. Balth. van der Pol, Jun., on the Production and Mea- 

 surement of Short Continuous Electromagnetic Waves . . 90 

 Prof. B>. W. Wood on Optical Properties of Homogeneous 



and Granular Films of Sodium and Potassium. (Plate I.) 98 

 Dr. Harold Jeffreys on the Force-Function in the Theory of 



Ordinary Relativity .. 113 



Dr. L. Silberstein : Further Contributions to Non-Metrical 



Vector Algebra 115 



Dr. T. J. Fa. Bromwich on Electromagnetic Waves 143 



Prof. Barton and Miss Browning on the liesonance Theory 



of Audition subjected to Experiments. (Plates II. &III.) 164 

 Dr. F. A. Lindemann on the Vapour Pressure and Affinity of 



Isotopes 173 



Dr. S. Chapman on the possibility of separating Isotopes . . 182 

 Prof. A. W. Porter and Dr. li. E. Slade on the Fundamental 



Law for the True Photographic Kendering of Contrast .... 187 



