The original polarizing prisms of petrographic microscopes were the early 19^th century design of William Nicol, and each was referred to as a Nicol prism (Bloss, 1961). When both Nicol prisms were introduced into the optic path in mutually perpendicular orientations, the examination was said to be using “crossed Nicols”. The phrase “crossed nicols” is still used for this geometry of polarized light, regardless of whether the polarizing optics use Nicol prisms or another polarization device.
See petrographic microscope, crossed polarizers