458 On the Light reflected by Potassium Permanganate. 



Fig. 1 is the absorption spectrum of a solution of potassium 

 permanganate in water. 



Figs. 2, 3, and 4 the reflection spectra, when the incident 

 light is polarized perpendicularly to the plane of incidence, 

 and falls on the surface at angles of 50°, 60°, and 70°. 



As has already been announced by Wiedemann, the position 

 of the bands in the reflected light depends on the nature of the 

 surrounding medium. From the experiments I have made, it 

 appears that, with unpolarized light, the first dark band of the 

 reflection spectrum corresponds in position with the first bright 

 band of the absorption spectrum, whether the permanganate 

 is in air, benzene, or either bisulphide or tetrachloride of car- 

 bon; these liquids, however, act on the permanganate, and 

 after a short time the surface becomes altered, and then the 

 bands correspond with the dark bands of the absorption spec- 

 trum. 



Figs. 4 and 5 represent the distribution of light in the spec- 

 trum, with fresh surfaces of potassium permanganate in bisul- 

 phide and tetrachloride of carbon, when unpolarized light is 

 incident upon them at an angle of about 55°: in both cases 

 the bands are wider apart than in air. 



