What you see here is a Charles Baker microscope with a Cooke microscope lamp providing Köhler Illumination. (The link is to my previous article explaining Köhler Illumination). I've implemented the crossed polarisation very simply.
A microscope used with crossed polarising filters is sometimes referred to as a polariscope.
In general, a polariscope is an optical inspection device used to detect internal stresses in glass and other transparent materials such as plastics, synthetic resins, crystalline materials, etc. A polariscope is composed chiefly of a light source and two crossed polarised lenses. Material to be examined is placed between the two polariscope lenses and viewed through the lens opposite the light source lens. It is commonly used in detecting the optical properties of gemstones.
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