The best Homepage in Old scientific Instruments : Museum of the History of Science, Broad Street, Oxford http://www.mhs.ox.ac.uk/
Epact is an electronic catalogue of medieval and renaissance scientific instruments from four European museums: the Museum of the History of Science, Oxford, the Istituto e Museo di Storia della Scienza, Florence , the British Museum, London, and the Museum Boerhaave, Leiden. Together, these museums house the finest collections of early scientific instruments in the world. http://www.mhs.ox.ac.uk/epact/
Rare books online. The e-rara.ch platform makes digitized rare books from Swiss libraries available to the public, free of charge.
Collection of links regarding scientific instruments in the Web: https://www.pinterest.com/geometricum/scientific-instruments-in-the-web/