Plate II, No. 1. Absorption spectra of' equivalent strengths of 

 solutions of the nitrate and chloride of Erbium. The ratio of the 

 dilutions is 1 : 719*8. Just as in the salts of Didymium in Plate I, 

 No. 1, also here the chief differences are seen in the strong solution 

 of the nitrate of Erbium. 



Plate II, No. 2. Absorption spectra of equivalent strengths of 

 solutions of the nitrate and chloride of Erbium ; and the ratio of 

 the dilutions is 1 : 244-8. The differences in the strong solution 

 of the nitrate from the other solutions can be easily seen. 



The photographs taken in tubes of 612 mm. length and the cell 

 of 5 mm. width, i.e. the solutions being in the ratio of 1 : 122-4, shew 

 similar differences. 



