Andrew Ross Monocular Compound Microscope Andrew Ross was a skilled English optician who crafted the monocular compound microscope sometime between 1841 and 1842. The illustration of the instrument provided was drawn from photographs of the original microscope, which was described by Gerard Turner in The Great Age of the Microscope. A compass joint with a clamping screw holds the limb of the brass Ross microscope to the instrument’s short pillar and base. A bearing at the end of the pillar enables rotation and inclination of the instrument. The optical system of the microscope consists of a Huygenian eyepiece and an unsigned objective that was inspired by the achromatic lens designs of Joseph Lister. Attached to the lower part of the microscope’s limb by a brass bar, a plano-concave mirror may be adjusted to gather light. The Ross microscope also features a mechanical stage with an upper plate that rotates and slides as needed. Beneath the stage, a three-aperture rotating disc facilitates control of specimen contrast, resolution, and illumination.

A rackwork mechanism, which moves the monocular body tube and is mounted on a dovetailed slide, may be manipulated to achieve coarse focus, while a short lever attached to the nosepiece of the instrument controls fine focus. During the period from 1837 to 1841, Ross worked in partnership with Lister and their joint efforts helped transform the microscope from a toy or parlor oddity into an important scientific tool. However, upon dissolution of the collaboration, Ross formed his own optical instrument firm. Unlike devices he constructed during the Lister partnership, the monocular compound microscope featured here bears a serial number. The inscription “No. 73,” along with the engraving “Andw Ross London,” is a clear indication that the instrument is an independent production of Ross constructed at his shop on Regent Street in London. Pacini-Style Italian Compound Monocular Microscope Filippo Pacini was an Italian instrument maker who excelled in microscope design and construction during the mid nineteenth century.

The microscope illustrated below is an example of the microscopes produced by Pacini. An original version of the microscope was photographed and described by Gerard Turner in his book Catalogue of Microscopes. The base is a flat semi-circular brass plate, supported by three short tapered feet, with the limb and two large columns emerging from the flat surface. An oval stage housing is positioned at the top of the columns and has plenty of room to accommodate a wide spectrum of specimens. The back portion of the stage is supported by a large rectangular brass limb, which contains a trapeze-sectioned bar carrying the arm to which the body tube is attached. This inner bar is attached to a locking screw that controls a long vertical iron screw serving as the fine focus mechanism through a knurled wheel positioned under the base. A circular stage has 360-degrees of rotation and can be translated in the Y-direction by a screw with a calibrated wheel on the back of the pillar. Below the stage is a set of four apertures and a single-lens condenser that can travel up and down on a brass rod. Light is projected into the condenser lens by means of a plano-concave mirror.