81 



XIV. — A New Application of Polarized Light in examining every 

 description of Objects. By John King, Esq. 



(Read November 11, 1846). 



Take for an analyzer a double-image prism, of moderate separating 

 power, and place it over the eye-piece of the instrument. 



The field will then appear to be edged by two areas of less intensity 

 than the centre, occasioned by the duplication of the circle of light. 



Next put upon the stage a plate of selenite, which exhibits, under 

 ordinary circumstances, the red ray in one position of the polarizing 

 prism, and the green ray in another, and each arc will assume one of 

 these complementary colours, whilst the centre of the field will remain 

 perfectly colourless. 



Into this field introduce any microscopic object ; and, whatever its 

 structure, it will exhibit the effects of polarized light, with great in- 

 tensity and purity of colour. 



In this way, many objects which, in the usual arrangement of the 

 polariscope, undergo no change in colour, are made to display the 

 most brilliant effects. 



Sections of wood, feathers, Alg& and scales, are among the objects 

 best adapted to this kind of exhibition. 



By substituting selenite that shows a variety of colours, the effects 

 are still more gorgeous. 



The best power for the purpose is a two-inch object-glass, the intensity 

 of colour as well as the separating power of the prism being impaired 

 under much higher amplification, although in some few instances, 

 such as in viewing animalculae, the inch object-glass is, perhaps, to be 

 preferred. 



The following appears to afford an explanation of this remarkable 

 fact ; but diffident of my own opinion, I respectfully submit it to the 

 notice of those members of the society who have made the subject of 

 polarized light their study. 



This phenomenon is attributable to the double-image prism separat- 

 ing the constituents of the polarized ray into two planes, and causing 

 them to overlap each other, except at the edges where the light is 

 analyzed; and, of course, the combination of the complementary colours 



