Monocular Compound Microscope, by J. Bleuler, London, Late 18th Century

This copper alloy instrument stands compass joint on a flat, folding tripod foot. The pillar has a triangular cross section and rackwork is cut into the rear facing side so the stage and its mounting can to be moved up and down for focusing. A sliding collar carries a substage condensing lens on a pivoting mount and a second collar carries the plano-concave lens on a horseshoe mount. The circular stage is recessed and has five pinholes, one of which is square. An arm fits into a slot at the top of the pillar. The body tube screws into a ring at the end of the arm. Below the arm is a rotating disk, on a click-stop mechanism, with six objective lenses.