Jarl A. Wasastjerna. 



(LXIV 



a = the percentage of light intensity which. is absorbed 

 by a crystal lamina 1 mm in thickness. 



/? = the percentage of light intensity which passes through 

 a crystal lamina 1 mm in thickness. 



n — the coefficient of absorption (according to the for- 

 mulae 1; unit of length = 1 mm.) 



u = ;t 



Diagrams 11^ — V set forth in polar coordinates the quantities 

 a, (i, X and //. respectively as functions of the angle g, which 

 the plate examined and consequently also the oscillatory 

 direction of the e-ray forms with the axis of the crystal. The 

 curves a = f{g), ft = f{g) and y. = f{g) are particularly 

 complicated although all these figures constitute section- 

 curves of rotation bodies formed by a plane passing through 

 the axis. The last named circumstance follows from the 

 agreement between corresponding values, obtained for the 

 two plates parallel to prism facets of the first or second order. 

 On the other hand the function /x is found to be of a partic- 

 ularly simple character as it constitutes an ellipse, and thus 

 only the axes and the eccentricity of the ellipse are functions 

 of the wave-length of the ray of light in question. The devi- 

 ations from mathematically perfect ellipses are small and 

 cannot be considered of theoretical importance. 



Tahle I. 



