Sir George Beatson and the Royal Beatson Memorial Hospital.

London instrument trade; their products included the early tripod and Marshall microscopes made of leather and wood; though in the eighteenth century the principal material of construction was brass. In Scotland John Finlayson was probably the first maker of microscopes (1743), and his compound microscopes were followed by a unique group of brass or silver simple microscopes made by John Clark. His development of the simple microscope was important, for this instrument offered significant optical advantages over the compound microscope which led to its use for research. Early in the nineteenth century simple microscopes were being used by men such as William Sharpey (1802-1880) and Robert Brown (1773-1858); while in Edinburgh Alexander Adie, an instrument-maker working under the instruction of Sir David Brewster (1781-1868), was making simple microscopes fitted with jewel lenses. Adie was also the maker of a reflecting microscope a design representing an attempt to improve the optical performance of the uncorrected compound microscope. A breakthrough came with the introduction of achromatic microscope objectives in the years 1825-1850, and Alexander Adie was one of the first of the provincial opticians to sell instruments of this type, which had been initially developed in London and Paris. Some of Adie's instruments copied the designs developed in Paris, though in addition many such microscopes were imported, particularly for medical use. Scottish microscopists also used instruments made by the London opticians. Notable examples of surviving London-made microscopes from this period are the Ross stand used by Balfour which is in the Royal Scottish Museum, and that made by Smith and Beck for Joseph Lister, now in Glasgow's Hunterian Museum. This last instrument, made in 1842, clearly illustrates the progress made in instrument design in the previous few years: for it has a curved Lister limb, substage condenser, and numerous accessories, as well as greatly improved optics. It is possible to assess the performance of the newly introduced achromatic objectives of this period by the measurement of their Optical Transfer Function. This procedure, which compares the contrast inherent in a test target with that in the image formed by the optics, shows that objectives of moderate apertures, such as were used by Lister for his early researches, have an optical performance nearly equal to that of modern objectives of equivalent aperture. Such data serve to demonstrate the significance of the optical improvement achieved in the early nineteenth century, and further emphasize that instruments preserved in museums are important for our understanding of the development of science and medicine.