översikt av Finska Vetenskaps-Societetens Förhandlingar. 

 Bd. LXIV. 1921—1922. Avd. A. N:o 1. 



On Light-absorption in a Pleochroitic Uniaxial 



Crystal (a Green Turmaline from Minas 



Geraes in Brazil). 



By 

 Jarl A. Wasastjerna. 



Communicated Sept. 19*^^ by W. Ramsay, Th. Homén 

 and Hj. Tallqvist. 



The following investigation which was conducted at the 

 Miiieralogical Institute of the University of Helsingfors, by pro- 

 position of Professor Wi 1 h. Ramsa y, aims at experiment- 

 aily ascertaining the dependence of light-absorption on the 

 wave-length and oscillatory direction of light in a pleochroitic 

 uniaxial crystal, or, to be precise, in a (not too strongly 

 pleochroitic) green turmaline from Minas Geraes in Brazil. 

 I take this opportunity to express my warmest thanks to 

 Professor Ramsay for his kindness in placing at my 

 disposal the apparatus of the Institute, and, above all, for 

 the interest which he has taken in my work. 



I carried out my investigation with the help of an appara- 

 tus pictured in Fig. I. At the point A there is an electrical 

 arc-light. By means of the lens-system B, which the figure 

 shows in diagram, we obtain a parallel beam of light which, 

 passing through a slit, falls into the spectroscope C, arranged 

 for obtaining monochromatic light. Through the slit D there 

 passes a regulated, narrow, parallel and practically mono- 



