CONTENTS OF VOL. XL, 



(SIXTH SERIES). 



NUMBER CCXXXV.-JULY 1920. 



P«g« 

 Prof. E. C. C. J3aly on Light Absorption and Fluorescence. — 



VI. Atomic and Molecular Energy Quanta 1 



Prof. E. C. C. Baly on Light Absorption and Fluorescence. — 



VII. Molecular Phases 15 



Prof. Frederick Slate on a New lieading of Relativity .... 31 

 Messrs. J. H. L. Johnstone and B. B. Boltwood on the 



Relative Activity of Radium and the Uranium with 



which it is in Radioactive Equilibrium . 50 



Prof. R. A. Sampson on the Bearing of Rotation on Relativity. 67 

 Dr. F. L. Mohler, Dr. Paul D. Foote, and Dr. H. F. Stimson 

 on Ionization and Resonance Potentials for Electrons 



in Vapours of Lead and Calcium 73 



Dr. Paul D. Foote and Dr. W. F. Meggers on Atomic Theory 



and Low Voltage Arcs in Caesium Vapour. (Plate I.) . . 80 

 Prof. A. R. Richardson on Stationary Waves in Water .... 97 

 Mr. A. C. Bartlett on Radiation from a Cylindrical Wall . . Ill 

 Miss Alice Everett on a Projective Theorem of Lippich's in 

 Geometrical Optics. (With a Note on the Equations 



of the Projection of a Straight Line on a Plane.) 113 



Prof. P. O. Pedersen on the Theory of Ionization by Collision 129 

 Mr. Bibhutibhusan Daita on the Stability of two Rectilinear 

 Vortices of Compressible Fluid moving in an Incompressible 



Liquid 138 



Messrs. F. B. Young, H. Gerrard and W. Jevons on Electrical 



Disturbances due to Tides and Waves. (Plate II.) 149 



Dr. Megh Nad Saha on the Secondary Spectrum of Hydrogen. 159 

 Dr. Norman R. Campbell on the Measurement of Time and 



other Magnitudes 161 



Mr. Balth. van der Pol, jun., on the Propagation of Electro- 

 magnetic Waves round the Earth 1 63 



