232 Mr. S. S. Richardson on Magnetic Rotary 



The magnitude of the variation, too, is as nearly as one can 

 -estimate of the right order ; and it is worth noticing that 

 the rapid change in intensity of scattering with wave-length 

 takes place over a range of wave-lengths approaching the 

 diameter of the atom. 



The possibility of a degradation of type — that is, a 

 lengthening of the wave-length — of radiation in the process 

 of scattering of long waves, and of an influence of a change 

 of intensity of the incident radiation on the process of 

 scattering, are points for further investigation. 



We wish to express our thanks to Mr. J. E. H. Hagger — 

 now Inspector of Munitions — for valuable help in these 

 •experiments. 



XXXI. Magnetic Rotary Dispersion in Relation to the Elec- 

 tron llieory. Part I. The Determination of Dispersional 

 Periods. By S. S. Richardson, B.Sc, A.R.C.Sc, 

 Lecturer in Physics, Central Technical School, Liverpool *. 



TT> ECENT developments of the electromagnetic theory of 

 JL\j dispersion, particularly at the hands of P. Drude, 

 H. A. Lorentz, and M. Planck, whilst differing with respect 

 to the mechanism to which the absorption is attributed, lead 

 to equations which are essentially of the same form, but 

 with constants of different meaning. The natural dispersion 

 in regions of the spectrum not bordering on absorption bands 

 is in each case represented by an equation of the Ketteler- 

 Helmholtz type, — 



a{K 2 a 2 \ 2 



or, separating the constant terms from those of a purely 

 dispersional character — 



^-^S^ + sA?* <*> 



In the visible and ultraviolet the effect of infra-red 

 resonators is almost negligible and the dispersion is found to 

 be controlled from bands lying in the ultraviolet usually, and 

 mostly in the Schumann region. As this portion of the 

 spectrum lies beyond the range of ordinary spectrographs, 

 and as moreover the work of Lyman f has brought to light 

 the prevalence of general absorption in this region, which 



* Communicated by Prof. L. R. Wilberforce, M.A. 

 t ' Spectroscopy in the Extreme Ultraviolet,' ch. ii. 



, aj/i a 2 /v 



J-— \2_\ 2 +Ti2_\ 2 T * ' " ' " * W 



