( 840 ) 



netisation : anioiiji' others some Itaiuls which were hardly visible 

 with Held off were inncli more pi-oiioniiced with the field on, in 

 contrast to most of the other cases observed. Further measurements 

 on this point are in |)rogress. 



It is quite probable that this product also contains other i';ire 

 earth-metals (e.g. dysprosium and holmium) ; this is, moreover also 

 rather likely for the other erbium salts. 



Erbium nitrate [Er {NO,),. QH.O]. 



§ 27. Here too, besides the amorphous salts (§ 10) monoclinic 

 crystal plates of an average thickness of 0.6 m.m. were examined, 

 containing both optical axes. The bands were finer than for any 

 sample examined befoi-e. On account of the very complicated reso- 

 lutions it was often somewhat difficult to ascertain to what bands 

 the different components belonged ; on exciting the field a sudden 

 confusion was observed from which the single bands slowly emerged 

 again on breaking the current. These observations were all made 

 with unpolarized light. 



The results are best arranged in a table in a way somewhat dif- 

 ferent from the above. 



Groap of hands in the green at — 193°. 



