viii Contents. 



PAGE 



The Dihydrotetrazines. By S. Kuhemann 316 



A Theory of the Widening of Lines in Spectra. By Prof. J. J. Thomson 318 

 On Secondary Rontgen Radiation. By Prof. J. J. Thomson . . . 322 

 The influence of a very strong magnetic field on the spark spectra of 



palladium, rhodium and ruthenium. By J. E. Purvis . . 325 



Experiments on the band-spectrum of nitrogen in a strong magnetic field. 



By J. E. Purvis 354 



On the ionization of gases exposed simultaneously to Rontgen rays and 

 the radiation from radio-active substances. By T. Nod A. (Com- 

 municated by Prof. J. J. Thomson) 356 



On the Measurement of the Earth-Air Current and on the Origin of 



Atmospheric Electricity. By C. T. B. Wilson .... 363 

 A suggestion as to the nature of the Horny Teeth of the Marsipobranchii. 



By H. W. Marett Tims . 383 



Proceedings at the Meetings held during the Session 1905 — 1906 . 387 

 Index 393 



PLATES. 



Plates I and II. To illustrate Mr Gregory's paper . . . .148 



Plate III. To illustrate Mr Peake's paper 250 



Plate IV. To illustrate Mr M c Dowall's paper 309 



