432 



WRIGHT— POLARIZED LIGHT IN THE 



Koenigsberger's Method.^ — In a series of articles Koenigsberger 

 suggested the use of a Savart plate^ in conjunction with an anal- 

 yzing nicol and a telescope for the detection of polarization in light 



reflected from a crystal surface, the 

 incident light to be non-polarized and 

 to impinge vertically on the plate. 

 The arrangement proposed by Koe- 

 nigsberger is illustrated in Fig. 7. 

 The non-polarized light (monochro- 

 matic or white) enters the system 

 along B, passes through a contrast 

 plate Q consisting of a bi-plate of 

 smoky quartz cut parallel to the axis 

 and mounted so that the axis is at 

 right angles in the adjacent halves ; a 

 lens L, for imaging the contrast plate 

 in the image plane of the telescope E. 

 The light passes through L to a small 

 reflecting prism R, thence through the 

 objective O to the crystal plate C 

 where it is reflected back through O 

 past R, through a plane-parallel, ro- 

 tatable glass plate P of known refrac- 

 tive index (w ^1.515), through the 

 Savart plate S and the nicol A'' into 

 the telescope E. 



The Savart plate consists of two 

 plates of calcite or quartz cut at an 

 angle with the optic axis sufficiently 

 large (45°) that if examined in con- 

 vergent polarized light the isochromatic 

 curves of the interference figure cross the field as practically straight 

 lines. The two plates are of equal thickness and are superimposed 

 so that the horizontal projection of the axis in the one is at right 



6 Centralblatt fur Mineralogie, Geologie u. PaVdontologie, 1901, pp. 195- 

 197; 1908, pp. 565-569, 597-605; 1909, pp. 245-250; 1910, pp. 712-713- 



^ Devised and first described by D. Brewster, Edinburgh Transactions, 9, 

 148, 1819; described later by Savart, Pogg. Ann. d. Phys., 49, 292, 1840. 



Fig. 7. Koenigsberger's ap- 

 paratus for the detection and 

 measurement of anisotropism 

 in opaque substances. 



