 the ordinary ray is eliminated and only the extraordinary ray is transmitted through the prism.It was the first type of polarizing prism, invented in 1828 by William Nicol (1770–1851) of Edinburgh.It consists of a rhombohedral crystal of Iceland spar (a variety of calcite) that has been cut at an angle of 68° with respect to the crystal axis, cut again diagonally, and then rejoined as shown, using a layer of transparent Canada balsam as a glue.