CONTENTS OF VOL. XV. — FIFTH SERIES. V 



Page 

 Proceedings of the Geological Society : — 



Mr. J. S. Gardner on the Lower-Eocene Section between 



Beculvers and Heme Bay 219 



Mr. F. Oats on Mr. Dunn's Notes on the Diamond-fields 



of South Africa 220 



Dr. H. Hicks on the Metamorphic and Overlying Rocks 



in parts of Eoss and Inverness shires 221 



Mr. E. Wethered on the Lower Carboniferous Bocks in 



the Forest of Dean 223 



Phosphorography of the Infra-red Eegion of the Solar Spec- 

 trum: Wave-length of the Principal Lines, by Henri 



Becquerel 223 



On the Measurement of the Photometric Intensity of the 



Spectral Lines of Hydrogen, by H. Lagarde 226 



Central Forces and the Conservation of Energy, by W. E. Browne 228 



NTJMBEB XCIV.— APEIL. 



Lord Eayleigh on Maintained Vibrations 229 



M. E. Pringsheim on a Measurement of Wave-lengths in the 



TJltra-red Eegion of the Spectrum of the Sun 235 



Prof. E. Warburg on Effects of Eetentiveness in the Magneti- 

 zation of Iron and Steel 246 



Eev. M. H. Close on the Meaning of " Force." •'. . 248 



Prof. J. J. Sylvester on the Number of Fractions contained in 

 any " Farey Series " of which the Limiting Number is given 251 



Mr. E. H. M. Bosanquet on Permanent Magnetism 257 



Dr. E. Tung on the Errors of our Sensations : a Contribution 



to the Study of Illusion and Hallucination 259 



Prof. W. F. Barrett on the Alleged Luminosity of the Mag- 

 netic Field 270 



Mr. E. H. M. Bosanquet on Self-Eegulating Dynamo-electric 



Machines 275 



Proceedings of the Geological Society : — 



Mr. E. A. Walford on the Eelation of the so-called 

 "Northampton Sand" of North Oxfordshire to the 



Clypeus-Grit 297 



Mr. D. Mackintosh on the Positions of Boulders rela- 

 tively to the Underlying and Surrounding Ground, in 



North Wales and North-west Yorkshire 297 



On Central Forces and the Conservation of Energy, by G. W. 



von Tunzelmann 299 



On the Refraction-Indices of Gases at High Pressures, by 

 J. Chappuis and Ch. Eiviere 299 



