Microscope No. 74 was designed to be used for the study of birefringent samples using Polarized Light Microscopy.
This Nicol prism in the eyepiece acts as the Analyzer for PLM.
This reticle, inserted into the base of the microscope body was used in conjunction with the rotating stage to measure crystal angles.
The lower end of the body tube can be rotated to align the internal reticle with crystal angles. The Vernier scale can be used to measure that angle.
The rotating stage is calibrated in degrees. It can be used to measure crystal angles.
From Hogg, 1898