Magneto-optic Phenomenon. 317 



Auxiliary Quantities determined by 

 J and H : — 



Auxiliary Quantities determined by Auxiliary Quantities determined by 

 J > H > « :— J, H, a :— 



*i,*2.^.Pi.^t. 



p, (i) t. 

 Observed Quantities : — 



<E>, -r = Azimuth of the polarization ' 



/ m(o) m(o) m(o) »i(o) 



produced. $i p ' ^,- a ' $i p ' ^a * 



Relations between the observed and 

 calculated values: — See §S 4, 5. 



* <r and t are determined by 



2H=r + o>; -cos2J= tan(7 -" j) : P =tanJ / cos2H 



tan(r + Wj) A/ C os(r-a»j)' 



sin" a sin 



2r 



t p and w are determined by 



cot2a>= — — cot2r; p 2 sin: 



sin 2 a sin 2r ct^ 



J The formulas for calculating these values are given in § 17. 



20. Although the relations of the amplitude and phase to 

 the angle of incidence are determined by the above observa- 

 tions, further investigation is necessary to ascertain the cause 

 of the very marked dispersion first found by Righi, and 

 which I also confirmed during my observations *. Further, 

 the theory just enunciated gives a simple relation between 

 the amplitudes of the magnetic components of the light on 

 polar and equatorial reflexion, so that it can be further verified 

 by this means. 



This research was carried out in the Physical Laboratory 

 of the University of Leyden. I have to thank the Director, 

 Prof. H. Kamerlingh Onnes, most heartily for the interest 

 which he showed during its progress, and for the many 

 acessories which were placed at my disposal. 



XXXV. On the Change in the Absorption-Spectrum of Cobalt 

 Glass produced by Heat. By Sir John Oonroy, Bt., M.A., 

 Fellow and Bedford Lecturer of Balliol College, and Millard 

 Lecturer of Trinity College, Oxford f . 



SIR David Brewster made some experiments on the 

 influence of heat on the absorbing power of coloured 

 media, and states in his 'Treatise on Optics' (edit. 1853, 



* It is remarkable that the dark band in the analyser never showed the 

 least trace of colour. 

 t Communicated by the Physical Society : read February 13, 1891. 



