Binocular Microscope, Van Heurck Type, by W. Watson & Sons, London, 1926

Van Heurck Type Binocular Microscope. The instrument is supported on trunnions on a heavy tripod base. The angle of the limb can be locked in place with a tightening screw operated by a steel lever. The top of the limb is shaped into an arm supporting the body. A copper alloy plate dovetails onto the arm, held in place by screws. Another plate slides in a dovetail slot in the first and is moved by a rack and pinion. The steel mounting for the binocular eyepieces and copper alloy body are screwed to this plate. A graduated, double mill-edged knob at the base of this arm operates the fine focus and two mill-edged knobs work the coarse focus. Three objectives screw into the rotating nosepiece. The 'circuit stage' consists of a rectangular, mechanical stage with steel spring clips to hold slides and two knobs to adjust its position, mounted on a copper alloy turntable. Below the stage a condenser with a variable aperture is mounted on a rack and pinion with a copper alloy knob for focusing. A copper alloy cylinder also extends below the stage and supports the plano-concave mirror.