COMPOUND MONOCULAR BAR LIMB MICROSCOPE-substage wheel of apertures.

MAKER: ANDREW ROSS

c.1843

The rectangular plate with a disk of apertures slides in along the bottom surface of the stage, held on by two fingers at the back of the stage bottom; this plate, like other substage accessories, has a screw in front to register in a a short round hole at the front of the stage, allowing adjustment for centering in the Y axis as well as providing a third point to hold the plate securely in place. The aperture wheel has four little brass knobs projecting down to rotate it into any of its four positions, each registered by a click-stop. There are three different size openings and one position that has no opening. Additional substage accessories, each on their own rectangular plate would slide into the same position.