MAGNUSSOX AXOMALOUS DISPERSION OF CTAXIX. 



251 



light are represented by the height of the respective ordinates. 

 The great dispersive power of fuchsin became at once apparent 

 on comparing lengths of the spectra produced by the dye and 

 by pure alcohol, that due to the latter being represented by the 

 dotted lines in the figure. For an IS per cent, solution of 

 fuchsin in alcohol, Christiansen obtained the following indices 

 of refraction: 



Table I. 



He worked' with solutions of different concentrations and 

 showed that the refractive index increases with the density of 

 the solution, but that this increase is different for the various 

 wave lengths. 



When Christiansen published his first results the subject was 

 taken up very energetically by Kundt, 1 who repeated the work 

 on fuchsin and examined many of the aniline dyes and other 

 colored solutions, such as indigo, carmine, and potassium per- 

 manganate. Many of these substances show "surface color," 

 that is, they have the power of reflecting certain colors more 

 than others. Kundt made extensive experiments to show the 

 interdependence of the two phenomena and came to the conclu- 

 sion that all substances which show "surface color" also give 

 anomalous spectra. Continuing his experiments he found that 

 a very close relation exists between dispersion and absorption, 

 and that anomalous dispersion depends upon the selective ab- 

 sorption of the medium and not upon the "surface color." This 

 discovery of the relation between absorption and dispersion has 

 been of the greatest importance and has enabled later investi- 

 gators to contribute much to our knowledge of dispersion. 

 Kundt embodied his conclusions in the following statement, 

 which is known as Kundt's Law, 2 to which no exception has as 



i Kundt, Pogg. Ann. CXLII., p. 163; CXLIII., pp. 149, 259; CXLIV., p. 128: CXLV., 

 pp. 67, 164. 

 a Kundt, Pogg. Ann. CXLIII., p. 265. 



