Leeuwenhoek seems to have been fascinated by the marvels of the microscopic world, but the extent and quality of his work lifted him above the level of the dilettante. He was not, like Malpighi and Swammerdam, a skilled dissector, but turned his microscope in all directions; in the mineral, as well as the vegetable and animal kingdoms. Just when he began to use the microscope is not known; his first publication in reference to microscopic objects did not appear till 1673, when he was forty-one years old. He gave good descriptions and drawings of his instruments, and those still in existence have been described by Carpenter and others, and, therefore, we have a very good idea of his working equipment. During his lifetime he sent as a present to the Royal Society of London twenty-six microscopes, each provided with an object to examine. Unfortunately, these were removed from the rooms of the society and lost during the eighteenth century. His lenses were of fine quality and were ground by himself. 'They were nearly all simple lenses of small size, but considerable curvature, and needed to be brought close to the object examined. He had different microscopes for different purposes, giving a range of magnifying powers from 40 to 270 diameters and possibly higher. The number of his lenses is surprising; he possessed not less than 2-47 complete microscopes, two of which were provided with double lenses and one with a triplet. In addition to the above he had 172 lenses set between plates of metal, which gives a total of 419 lenses used by him in his observations. Three were of quartz, or rock crystal, the rest were of glass. More than one-half the lenses were mounted in silver, three were in gold.
It is to be understood that all his microscopes were of simple construction; no tubes, no mirror; simply pieces of metal to hold the magnifying-glass and the objects to be examined, with screws to adjust the position and the focus. We shall perhaps get the best idea of how they were used and brought into focus by reference to Fig. 7, which is copied from Richardson's article in 'The Asclepiad." This shows the way the instrument was arranged to examine the circulation of blood in the transparent tail of a small fish. The fish was placed in water in a slender glass tube, and the latter was held in a metallic frame, to
