. The London, Edinburgh and Dublin philosophical magazine and journal of science. he dark bands of the absorp-tion spectrum, instead of with the bright bands as they dowhen the angle of incidence is about 55° or less. The shaded portions of the diagrams are intended to givethe relative amount of light, as determined by eye estimations,in the different portions of the absorption and reflectionspectra of potassium permanganate—the ordinates being takento represent the intensity, and the abscissa wave-lengths. Thecurved line gives the intensity of the light in the differentportions of the normal
. The London, Edinburgh and Dublin philosophical magazine and journal of science. he dark bands of the absorp-tion spectrum, instead of with the bright bands as they dowhen the angle of incidence is about 55° or less. The shaded portions of the diagrams are intended to givethe relative amount of light, as determined by eye estimations,in the different portions of the absorption and reflectionspectra of potassium permanganate—the ordinates being takento represent the intensity, and the abscissa wave-lengths. Thecurved line gives the intensity of the light in the differentportions of the normal spectrum, as determined by Mossotti *from Fraunhofers measurements, neglecting the minor irre-gularities in the curve as given by him.* Pogg. Ann. lxxii. p. 509. 458 On the Light reflected by Potassium Permanganate. Fig. 1 is the absorption spectrum of a solution of potassiumpermanganate in water. Figs. 2, 3, and 4 the reflection spectra, when the incidentlight 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 positionof the bands in the reflected light depends on the nature of thesurrounding medium. From the experiments I have made, itappears that, with unpolarized light, the first dark band of thereflection spectrum corresponds in position with the first brightband of the absorption spectrum, whether the permanganateis in air, benzene, or either bisulphide or tetrachloride of car-bon; these liquids, however, act on the permanganate, andafter a short time the surface becomes altered, and then thebands 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 isincident upon them at an angle of about 55°: in both casesthe bands are wider apart than in air. [ 459 ] LIX. On a possible
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