Antonie van Leeuwenhoek
Techniques

Antonie van Leeuwenhoek made more than 500 optical lenses. He also created at least 25 single-lens microscopes, of differing types, of which only nine have survived. These microscopes were made of silver or copper frames, holding hand-made lenses. Those that have survived are capable of magnification up to 275 times. It is suspected that Van Leeuwenhoek possessed some microscopes that could magnify up to 500 times. Although he has been widely regarded as a dilettante or amateur, his scientific research was of remarkably high quality.

The single-lens microscopes of Van Leeuwenhoek were relatively small devices, the largest being about 5 cm long. They are used by placing the lens very close in front of the eye. The other side of the microscope had a pin, where the sample was attached in order to stay close to the lens. There were also three screws to move the pin and the sample along three axes: one axis to change the focus, and the two other axes to navigate through the sample.

Van Leeuwenhoek maintained throughout his life that there are aspects of microscope construction "which I only keep for myself", in particular his most critical secret of how he made the lenses. For many years no one was able to reconstruct Van Leeuwenhoek's design techniques, but, in 1957, C. L. Stong used thin glass thread fusing instead of polishing, and successfully created some working samples of a Van Leeuwenhoek design microscope. Such a method was also discovered independently by A. Mosolov and A. Belkin at the Russian Novosibirsk State Medical Institute. In May 2021, researchers in the Netherlands published a non-destructive neutron tomography study of a Leeuwenhoek microscope. One image in particular shows a Stong/Mosolov-type spherical lens with a single short glass stem attached (Fig. 4). Such lenses are created by pulling an extremely thin glass filament, breaking the filament, and briefly fusing the filament end. The nuclear tomography article notes this lens creation method was first devised by Robert Hooke rather than Leeuwenhoek, which is ironic given Hooke's subsequent surprise at Leeuwenhoek's findings.

Van Leeuwenhoek used samples and measurements to estimate numbers of microorganisms in units of water. He also made good use of the huge advantage provided by his method. He studied a broad range of microscopic phenomena, and shared the resulting observations freely with groups such as the British Royal Society. Such work firmly established his place in history as one of the first and most important explorers of the microscopic world. Van Leeuwenhoek was one of the first people to observe cells, much like Robert Hooke. He also corresponded with Antonio Magliabechi.
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