The image from the objective is split into two beam paths by this Wenham prism.
The prism is placed behind the nosepiece (below). It was useful only for long focal length lenses (1/2 or longer). When using high magnification lenses the prism is removed, and the microscope transformed into a monocular microscope.
Binocular tubes of this era were not symmetrical; instead they had one tube separate laterally off the main vertical body tube. Light was split by the Wenham Prism