A LARGE VICTORIAN LACQUERED BRASS COMPOUND MINOCULAR POLARISING MICROSCOPEWATSON BROTHERS, LONDON, CIRCA 1885The body tube assembly fitted with a prism/filter slide aperture beneath fine screw focus at the eyepiece end, the junction with the 'Lister' type limb with rack-sliding primary focus adjustment incorporating Vernier distance scale calibrated in inches divided into fiftieths, the circular stage with X and Y diagonal subject positioning, slide clips mounted within dovetail grooves and calibrated in degrees of rotation to outer edge, the subs stage assembly with swing-out condenser lens incorporating a prism set within rotating bezel and the underside with pivoted plano-concave mirror mounted on a double-jointed pivot, the whole raised via pivoted axis support on a complex cast base with twin uprights and integral Y-shaped stand engraved WATSON BRO'S:, 4 Pall Mall, London, 5192 to the rear, in a mahogany box with three body tube filter slides only, (lacking all lenses except the substage condenser).The box 40.5cm (16ins) high, 24cm (9.5ins) wide, 20cm (8ins) deep.According to the Virtual Museum of the History of Minerology the present model of microscope was developed in London in 1879 by Thomas William Watson (son-in-law of William Tranter, gunsmith of Birmingham). The instrument was designed in collaboration with the renowned geologist Frank Rutley and was probably one of the earliest professional quality polarizing instruments made in England. Thomas was joined in business by his brother in around 1885 and the name was changed to Watson Brothers. This example comes from about this time.