220 



Mr. W. B. Cartmel on the Anomalous 



by the })rism method, and by Walter* by the method of total 

 reflexion. 



X. 



Pfliiger. 



Walter. 



Interference metbocl. 



A ... 





2-019 



2-055 



« 





2-086 



2-12 



706... 



2'3i 





215 



B ... 



... 



2-r61 



222 



Li ... 



2-34 





2-27 



C ... 





2-3] 



2-35 



634... 



... 



2-412 



2-48 



D ... 



2-64 



2-684 



2-70 



535... 



1-95 





1-98 



E ... 





1-912 



1-85 



F ... 



1-65 



1-074 



1-05 



Sr ... 



0-83 





0-82 



455... 





0-847 



0-83 



a ... 



104 



0-95 



1-00 



425... 





1-00 



1-11 



H ... 





1-32 





The curve is uncertain within the absorption-band and 

 perhaps also to some extent in the violet^ but in the red end 

 of the spectrum it is established beyond a doubt that the 

 values given by Pfliiger do not apply to the fuchsin upon 

 which my measurements were made. The fact that Pfliiger 

 obtained the same values using prisms of different angles 

 seems to show either that the two methods lead to different 

 results, or that the composition of the two samples of fuchsin 

 was different. There are a number of red triphenyl methane 

 dyes of distinctly different compositions, all of which go under 

 the name of fuchsin. Wernicke f obtained the dispersion- 

 curve of a fuchsin by the prism method, and found the in- 

 dices to range from 1'31 to 1*90. The one on which the 

 writer^s first work was done had indices ranging from less 

 than unity to about two. Kundt experimented on a fuchsin 

 having two absorption-bands in the visible spectrum. How- 

 ever, there is no doubt but what the fuchsin in question was 

 made by the same process as that which Pfliiger used, though 

 having been purchased seven ^^ears later it was probablv 

 made in a different batch, and hence there is a possibility of 

 the composition being slightly different. 



The agreement with Walter in the red is extremely satis- 

 factory. The two curves run uniformly parallel to one 

 another, the author's being a little higher than Walter's, 

 which may be accounted for by an error in the thickness or 



* Wied. Ann. Ivii. p. 396 (1896). 

 t Pogg. Ann. civ. (1875). 



