242 SIR DAVID BREWSTER ON THE 



Azimuth 315°. Light +45°— 45°. E' is polarised 59° to right, and 0' 69° 

 to the left. 



Azimuth 322°. Light + 45°— 45°. E' polarised 61° to right, and 0' 83° to right. 



Azimuth 180°. Light +45° — 45°. E' is polarised 5(H° to left, and 0' 58° to 

 right. 



Azimuth 0°. Light 0° and 90°. E' is polarised 90° out of the plane of reflexion, 

 0' vanishing with 0. 



Azimuth 180°. Light 0° and 90°. E' is polarised to the left, about 86°, 0' 

 vanishing with 0. 



Azimuth 270°. Light 0° and 90°. E' and 0' polarised 21° to the right. 



Azimuth less than 270°. Light 0° and 90°. E' and 0' polarised 8° to the right. 



With Oil of Anise Seeds. 



Azimuth 0° and 180°. When the prism pencil with common light vanishes, 

 the spar pencil is very bright, and a great deal of light, namely, reddish light 

 is polarised in the plane of reflexion. 



Azimuth 90° and 270°. The spar pencil is completely polarised about 7° to 

 the left. 



In the azimuth, between 90° and 180° perpendicular to the edge beside the 

 obtuse angle, change of polarisation varies from 45° of incidence where it is 0°, 

 up to great incidences, where it is about 45° or 50° to the left, the pencil being 

 there completely polarised. Between azimuths 270° and 360°, the change varies 

 from 125° to 100° at great incidences, but the pencil is nowhere completely 

 polarised. 



With Alcohol. 



At Azimuths 0° and 180°, there is no change of polarisation, but the spar 

 image is polarised at a much less angle of incidence than the prism image, 

 whereas at azimuth 90°, they are polarised at the same incidence. 



E. Face inclined 67° 30' to the Axis. 



In Azimuth 0° and 180°, the change of polarisation is 90°, the polarisation 

 being more complete, by considerably increasing the incidence. 



The change of polarisation increases from azimuth 0° to azimuth 90°, diminishes 

 from 90° to 270°, and increases from 270° to 369°. 



In Azimuth 0° and 180°. At the polarising angle only half the pencil is 

 polarised 90° out of the plane of reflexion, the other half appearing to be polarised 

 in another plane. 



Azimuth 0°. Light +45° — 45°. E' is polarised 45° to the right, and 0' 61° 

 to the left. 



I 



