This interesting instrument is a brass monocular compound microscope manufactured by Powell and Lealand. It is referred to as a “Student’s Compound Microscope” because of simple design and cast iron, 3-pronged base & pillar. It is unusual primarily due to the lever-adjustable stage and white metal body tube. The tube is signed “Powell & Lealand, London”.
The microscope consists of a brass body tube set inside the white metal outer, support tube. Coarse focus is via rack & pinion, with the focus knob fastened to the outer support tube. The rack is integral to the body tube so that when the knob is turned the body slides inside the white metal support tube. Fine focus is by the short-lever mechanism controlled by a knob on the side. The stage consists of two levels: a fixed lower platform and a gliding upper, sample stage level. The X and Y movement is actuated by the Varley mechanism*. There is one substage mirror supported by a descending arm. Optics consist of a single Huygenian eyepiece and a single 3/4" objective lens. The instrument is 40cm high. The instrument can be stored in a large mahogany case (22x22x38cm). Imaging is very good, showing only a slight amount of chromatic aberration.
Hugh Powell (17991883) was an instrument maker residing at 24 Clarendon St., Somers Town, London. His first recorded contribution to microscopy was a precision microscope stage introduced in 1832. The following year he added fine adjustment to the stage movement. Hugh Powell continued to make microscope components under his own name until 1841 when the RMS ordered three microscopes; one each from Powell, Andrew Ross, and James Smith. The Council of the Society intended for these makers to create instruments that represented the best design principles of the day. This event catalyzed the partnership of Powell and his brother-in-law P.H. Lealand, and on Dec. 22, 1841 Powell & Lealand delivered their first microscope to the RMS. Their new instrument predicted the design that appeared a few years later. The London Physiological Journal, Nov. 1843, described it as being "...the first instance of a Microscope hanging in a tripod in the same way that a kettle hangs from a tripod of sticks in a gipsy's (sic) encampment... This is also the first Microscope where the fine adjustment moves the nosepiece by means of a lever inside a bar movement..." They created a large brass instrument incorporating a tripod base, trunnion-supported main tube, rack coarse focus, "long-lever" fine focusing, and compound substagea design that remained their basic instrument model for over 60 years. After the death of Hugh Powell, his son Thomas Powell continued the firm creating microscopes, and especially high-quality objectives. "Many Fellows of the Society will recollect the 1/40th objective which he was accustomed to exhibit on Pond Life nights, and which he made when over 70 years of age." The firm of Powell & Lealand ended with the death of Thomas Powell in 1924.
Varley stage invented by Cornelius Varley allowed smooth X and Y movement using one actuator arm. (Varley, Cornelius. "Mr. Varley's description of his New Lever Movement", London Phys. J. 12/1843. pp. 9496.)
Microscope featured 09/2012