Using

With difficulty, Leeuwenhoek used his microscopes to make the world of microorganisms visible.

Ingenuity

Like so many of his countrymen, Antony Leeuwenhoek was ingenious. The Dutch people of his time developed innovative:

• uses for the windmill such as long boards for large ships
• designs for ships to carry more cargo with fewer crew members
• methods of financing long, expensive ocean voyages

During the 1600's, no one did those things as well as the Dutch.

Leeuwenhoek, the curious, clever draper from Delft, made his own innovations. He learned how to make and mount tiny glass lenses with minimal aberration that still had enough magnifying power and resolution to make his specimens visible. No one did those things as well as Leeuwenhoek.

He looked at salt crystals or a pig's liver or a dragon-fly's eyes with lenses magnifying up to two hundred times. He was able to view and describe bacteria which were less than 2 µm in diameter. If the lens was small enough, round enough, and clear enough and turning the screws let the specimen come into focus, magnification and resolution were possible. Visibility, however, was a separate and more difficult problem.

With our industrial, high-tech, science-as-expensive-business perspective, we must make an effort to understand that the world Leeuwenhoek was revealing was new and unprecedented. He had one foot in the world of spirits, crafts, guild secrets, and alchemical mysteries. And the other foot in the world of mechanical laws, mathematical proofs, and unbelievably large numbers. Galileo was also secretive about his methods, and his results were also hard to reproduce at first. Leeuwenhoek's contemporary Isaac Newton (1643 – 1727) was an alchemist.

Just as his countrymen collected cabinets of curiosities gathered from around the Earth, Leeuwenhoek collected cabinets of curiosities gathered from his body, around his house, and from the canal in front of his house. Without the microscope accompanying it, his collection to the naked eye was just water in a thin tube or a bit of dried animal tissue, not very interesting in themselves. However, with the microscope, Leeuwenhoek's cabinets of wonders were visible to anyone. Or at least those who had patience and good eyesight.

In one of his last letters (1722), he wrote:

Whenever I make any Discovery, which I apprehend will not easily meet with Credit, I suffer the Object to lie before the Microscope Day after Day, and sometimes for whole Years together, till it is eaten up by Insects. This I do with design to let it be seen by as many different Persons as possible.

There was no standardization in 1722. There were no boxes of interchangeable parts for Leeuwenhoek to reach into. Each lens was different. A given lens might work well for one specimen yet be too strong or too weak or too aberrant to see what he wanted to see with the next specimen.

His lens-making skills were also evolving. He could only make them so small. Since he saw bacteria early in his career, and never saw anything smaller, he reached the size limit early on. However, by continuing to make lenses, dozens and dozens of them, he continued to make them better, which means clearer glass and more regular surfaces rather than stronger (smaller).

And finally, he kept evolving his methods of observation. It was his art, and there was no more reason to reveal it than for Vermeer to reveal the "secrets" of his use of perspective or his recipes for color pigments. But if you had Leeuwenhoek's years of patient use, then the secrets would reveal themselves to you. In a letter published in 1720, he wrote:

Nor should I ever have attained thereto, but by continual Labour in the investigation of things, which are concealed from our naked Eyes, and towards which I have a much greater inclination, than what I observe in most other Men.

How did Leeuwenhoek hold his microscopes?

To give a sense of scale, this photo shows a full-scale replica Leeuwenhoek microscope in use by Huib van Duin. His eye should probably be closer because the eye point of a Leeuwenhoek microscope is shorter than most people's eyelashes.

Having used a replica, I found that holding it off to the side let my eye get even closer. In his letters, Leeuwenhoek frequently mentions "sticking" and "gluing" specimens to the pin. As long as the specimen was securely fastened, it would not fall off.

In any event, we have no evidence of which position Leeuwenhoek used. Given the length of time he had to keep observing, he may well have used both hands in a variety of positions.

On the close inspection of 3 or 4 drops, I may indeed expend so much labor that the sweat breaks out on me.