( 843 ) 



38 Kilogauss. — Plane of polarisation horizontal — Thickness 0,6 mm 



Here I and III yielded very blurred doublets, of which the distances * 

 of the extreme limits are given; V a distinct doublet with a shade 

 between the components, perhaps a quadruplet. 



With a vertical plane of polarisation the phenomenon was analogous 

 and was confirmed with a thinner plate : I was a doublet, III was 

 invisible here, with IV some light appeared in the middle with 

 greater widening, structure probably complicated, V was again a 

 very distinct doublet. 



Group of bands in the red at — 193°: Four bands, among which 

 two rather sharp ones 674,4 and 676,2 showed a widening or a 

 fading away in the field ; the last-mentioned became a doublet, 

 perhaps even a quadi'uplet, with plane of polarisation vertical. 



Neodymium nitrate [^Nd{NO^)i . 6 i/,0] . 



§ 24. It appeared important to investigate crystals besides the 

 amorphous nitrate (^ 9j ; with a much slighter thickness crystals show 

 intense and narrow absorption bands; the natural monoclinic plates 

 were directed perpendicularly to one of the optical axes, so that in this 

 case a nicol could be done away with. The wave-lengths of the 

 bands are on the whole slightly less — down to 3 fif* — for the 

 nitrate than for the sulphate. 



Band in the blue-green at — 193°. The wave-length now was 

 ^ =: 51 1 ,3 fi|t ; in a field of 41 kgs. a doublet appeared, the compo- 

 nents of which had a distance of 0,22 mi. 



Group of bands in the green at — 193". 5 bands were measured 

 in the spectrum of the second order. 



