420 Dr. Leeson on the Circular Polarization of Light 



the bundle A is divided into two portions, O and X ; and 

 it will be observed that O, proceeding in its original course, 

 is transmitted or passes through the second bundle B, fig. 1, 

 whilst X is reflected from, and does not pass through, the 

 bundle C. The converse takes place in fig. 2. Hence it 

 will be observed that in fig. 1 the portion O is capable of 



Fig. 1. 



K 



\ 



^0 



Fig. 2. 



\ 



O 



transmission but not of reflexion, whilst the portion X is ca- 

 pable of reflexion only. In fig. 2, where the bundles B and 

 C are supposed to be placed at right angles to the bundle A, 

 the portion O is capable of reflexion only, and X of trans- 

 mission. In these figures A forms what is termed the po- 

 larizer, whilst B and C are what are termed analysers, serving 

 to test the condition of O and X. 



A tourmaline effects a similar division of a beam of light 

 impinging on it, into two portions oppositely polarized, trans- 

 mitting one, say O, in one position, whilst X is absorbed : re- 

 volving the tourmaline 90°, X will be transmitted and O ab- 

 sorbed. For experiments on circular polarization, as well as 

 for microscopic purposes, the green tourmalines may be re- 

 commended, as they can be more easily obtained free from 

 flaws. When of a proper thickness and ground truly parallel. 



