MAGNUSSON — ANOMALOUS DISPERSION OF CYANIN. 



285 



Table X. 



The two photographs used for tables IX and X were taken 

 with the same cyanin film in one path of the interferometer. 

 The relation between fi and a as given in tables IX and X is 

 shown graphically in the curve of plate 17 by the full line, while 

 the dispersion curve obtained by direct spectrometer readings is 

 indicated by the broken line. These curves, obtained by en- 

 tirely independent methods, agree very well, and the difference 

 is probably due to a change in the properties of the substance 

 in the two conditions, for the cyanin was fused in the one case 

 and deposited from an alcoholic solution in the other. It is im- 

 portant to note the rapid rise in the curve when the absorption 

 band in the ultra violet is approached, as it shows a similarity 

 to the increase in the refractive index as the absorption band 

 fn. the yellow is approached from the red end of the spectrum. 



The results from measurements made on the photograph 

 shown in figure 1 of plate 22 are given in table XL 



