Pages tagged scientist

Leeuwenhoek's Microscopes

His microscope was a superior design because it solved his problems better than the alternatives. It was a dead-end design because it was too hard to make and much harder to use than the double-lens microscope.


Biologists today are seldom well-versed in the history of science. If they know anything about Leeuwenhoek, it's "animalcules", usually spoken with a little grin. So quaint! The word animalcules is a diminutive of animal. Its first use in English is 1599 and it wasn't used much after the mid-1880's. It referred to small animals, from insects to mice, but usually invertebrates. As the Google Ngram below shows, it was replaced by microbes around the time of Pasteur and Koch.

1673: Exceedingly curious and industrious

"About two years ago I observed the sting of a bee," he wrote in his first letter, dated April 28, 1673. Thus, by early 1671, Leeuwenhoek had learned how to grind lenses as well as almost anyone.

1674: Perhaps will to many seem incredible

In the spring of 1674, Leeuwenhoek was ready with new observations. In April's letters to Constantijn Huygens and Henry Oldenburg, he first turned his lens on the human body.

1675: A multitude of unarranged and promiscuous observations

Leeuwenhoek spent the year studying a variety of minerals, especially salts, and parts of plants and animals. Most commonly, he soaked things in well water and rain water. Sometimes, he let the things dry before he observed them. Taste became a theme.

1676: I discovered living creatures

Leeuwenhoek had a busy summer in 1676, making daily observations of water from various sources to learn when and under what conditions the little animals appeared. Where did they come from? How many were there? How long did they live? The result was the letter of October 9, which presented a convincing amount of evidence for the microbial world only he had explored, somewhere between Columbus and Adam.

1677: To confirm his observations

It was one thing for Leeuwenhoek to count how many and calculate how small. It was another thing for those without the lenses and the expertise, the members of the Royal Society, to believe him.

According to Descartes

Objectivity. As Descartes' Discourse on Method instructed, Leeuwenhoek was: careful to avoid precipitancy and prejudice, and to comprise nothing more in [his] judgment than what was presented to [his] mind so clearly and distinctly as to exclude all ground of doubt.

As Science Began

How the self-taught van Leeuwenhoek helped give birth to the scientific method, especially peer review.

Counting the Little Animals

How small? How many? How van Leeuwenhoek calibrated and counted the multitude of tiny things he discovered.

Dead-end design

Once Leeuwenhoek had the instrument, he had to learn how to use it. Using it was so difficult that his design was never used by anyone else to make important discoveries. In the history of the microscope, it was a dead end.

Eel viewer - showcase for visitors

The pin on Leeuwenhoek's simple microscopes did not work for large living specimens. For example, Leeuwenhoek's showcase for visitors was a demonstration of the blood circulating through the capillaries in the tail of an eel. The eel had to be living if the blood were to circulate and a living eel would not stay still on the edge of a pin. So what would you do?

Empirical Evidence

Repeatedly in his letters, Leeuwenhoek calls what he does waarnemingen, observations. His first question was always: What am I seeing? It was a new world that no human had ever seen before, so he had to describe it accurately.


How did the parts work together? Positioning screw: The longest screw moved the mount, and thus the specimen, in two directions: up and down and back and forth. Focusing screw: This shorter screw moved the mount, and thus the specimen, in and out, that is, closer to or farther from the lens. It did this by pressing against the body plate, pushing it away from the specimen pin.

Hooke's Three Tries

Robert Hooke, of whom no painted portrait survived, was a man of many interests and talents, not the least of which was drawing. He had paid some attention to the microscope when he published his groundbreaking and best-selling Micrographia in 1665. Its drawings, some of which were oversized foldouts, made it a best seller.

How to dissect animals and plants

The Dutch were interested in dissection of human bodies for both forensic and scientific purposes. City anatomists Cornelis 's Gravesande Collectors of rarities and curiosities noted in Engel who lived in Delft during Leeuwenhoek's lifetime:

Open publication

Fortunately, Leeuwenhoek lived at the first point in history when a medium was available for him to tell the world about his discoveries: the publications of the Royal Society in London. He wrote on June 12, 1716: Whenever I found out anything remarkable, I have thought it my duty to put down my discovery on paper, so that all ingenious people might be informed thereof.

Peer Review

"If they would expose any Errors in my own Discoveries, I'd esteem it a Service." - December 25, 1700

Period 2 - 1679-1686

The Letters from March 1, 1679, through December 31, 1686

Social context

Science is sometimes done today by people working in isolation for long periods of time. However, it is usually done with others, in groups and teams, regardless of nationality or social standing.

The consolation of little animals

Using a dead-end design, Leeuwenhoek had an instrument that was up to an order of magnitude better than anyone else had.

Validity of Process

Modern science accepts that: a valid process is one that produces the results it says it is producing. valid results are the outcomes of a valid process. when repeated, a valid process always, reliably, produces the same results. In Leeuwenhoek's time, these were revolutionary ideas. Where was the weight of authority? Aristotle? The Bible? These ideas about validity came from Francis Bacon and Rene Descartes, both of whom laid out the basic ground rules by which science still operates.