A N:o 1) On Lisht-nbsori)tion in a Pleochroitic Uniaxial Cryslal. 5 



In all experiments the same crystal was employed. First 

 two prism facets were ground, with the object of determining 

 the indices of refraction. 



For absorption experiments the crystal was ground afresh 

 successively in order to obtain plates with parallel facets, 

 forming with the axis the following angles: 



0°0', 11° 15', 22°30', 45°0', 67°30', 90°0', 



and related to the prism and pyramid faces of the first 

 order. Finally a plate was ground having facets parallel to 

 a prism face of the second order. The thickness of the latter 

 plate was 1,64 mm. 



All grinding was done by the MTiter personally, by the aid 

 of Wulfing's well-known apparatus, and during grinding 

 checking measurements were taken and corrections arising 

 therefrom carefully made. Only one facet showed an error 

 exceeding 4', namely 6' (22° 30' plate). None of these errors 

 are of any consequence. Particular importance was attached 

 to polishing, which was done with tin putty. The polished 

 facet was regularly examined microscopically and polishing 

 was continued so long as there remained the slightest scratch 

 or other blemish caused by grinding. 



A specially important question, on which the value of 

 the whole work essentially depends, is whether or not the 

 particular crystal employed may be considered as having 

 been practically homogeneous. A possibility of deciding this 

 question is afforded by the control which the quantity x^o 

 constitutes. Heterogeneousness of the crystal will of course 

 be at once revealed by the absence of constancy in x^^ . 

 Fluctuations in x^^ thus certainly indicate at least the 

 approximate extent of error in x^. 



Table I shows the indices of refraction n^^ and n^. 



Table II contains the experimental data obtained by the 

 aid of the apparatus pictured in fig. I, and the values, calcul- 

 ated on the strength of these data, of 



