As Science Began

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

In the 1600's, Western Europe was poised on the edge of the Enlightenment. Copernicus and Galileo had upset the old order and Newton had not yet established a new order. Looking back, we can see that the lines between science, superstition, and pseudo science were neither bright nor clear, especially in the universities.

Newton's alchemy cannot be isolated from Newton's science. In 1942, after reading the million words that Newton wrote about alchemy over two decades in until recently unpublished journals and personal notebooks, John Maynard Keynes told the Royal Society Club that "Newton was not the first of the age of reason. He was the last of the magicians." To the many followers of Descartes at the time, Newton's concept of "gravity" was too insubstantial, almost mystical, not mechanical enough.Hermes Trismegistus

Newton, along with the most learned academics, struggled to reconcile the received wisdom of the ancient texts to the perceived world around them. Aristotle, the Bible, and Hermes Trismegistus (image at right) told them one thing. Their telescopes, microscopes, prisms, and mathematical calculations told them something else.

At the Birth of the Scientific Method

What about Antony van Leeuwenhoek? To what extent was he a scientist, a man of empirical reason and not a "conjurer," as some in Delft called him, saying in a letter in 1677 "that I show people what doesn't exist"? To what extent was what he did science? That is, to what extent did he exhibit the behavior and values that we now associate with science?

Leeuwenhoek was also a man between worlds, the old world of scholasticism, alchemy, and superstition and the new world of rationality, science, and empiricism. We can assume that he knew the significance of what Galileo discovered and that he knew what had happened to Galileo as a result. During his life and even more since then, Leeuwenhoek has been denigrated as an amateur or as self-taught or even "the immortal dilettante" (L. M. Becking in Science Monthly, 1924). Why?

  • He never developed a theory to unify or explain his observations.
  • His observations, covering such a wide range of subjects, sacrifice depth for breadth.
  • He never wrote a book.
  • He had no students.
  • He did not have a degree from a university.
  • He did not even know Latin.

In other words, he did not have sufficient credibility for the old world of dogma and authority. However, he did have valid, reliable, original observations. He used a superior tool to become the first person to see and systematically record the microscopic world of protozoa and bacteria as well as many microscopic structures of the macroscopic world. He held values and practiced methods and techniques that are now associated with scientists.

In this definition, science is an activity, a method, a process for disproving hypotheses, for determining which ideas are right and which are wrong. This method has the following characteristics. The underlined terms are linked to the discussion below.

What makes science?

observations and experiments as primary sources
controlled experiments; accurate, quantified observations; laboratories
repeatable process, replicable results
peer review
nothing trivial or erroneous; only novel, substantial
open publication
scholarly journals, monographs
social context
transnational cooperation, societies of experts

Leeuwenhoek's activity, as recorded in his letters over fifty years, exhibits all of these characteristics.

Leeuwenhoek's scientific activity

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.

Leeuwenhoek's cabinet of wonders

All 140 figures, originally copperplate etchings on 32 plates that accompanied half the of 46 letters of the Send-Brieven. Organized by groups of specimens.

Counting the little animals

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


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.

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:

The Letters

The best way to learn about Leeuwenhoek's science? Read the letters!

Period 1 - 1673-1679

The 42 letters from Letter 1 of April 28, 1673 (AB 1), through Letter 27 of February 21, 1679 (AB 42) before Leeuwenhoek began publishing them himself. Of the 32 letters with scientific observations, 16 of them had a total of 65 figures. Of the 28 letters with scientific observations that he sent to the Royal Society, 17 were excerpted in Philosophical Transactions.

Period 2 - 1679-1686

The 54 letters from Letter 28 of April 25, 1679 (AB 43) through the letter of October 30, 1686 (AB 96). Of the 36 letters with scientific observations, 25 of them had a total of 219 figures. Leeuwenhoek published 25 of these letters in Works I.

Period 3 - 1687-1694

The 42 letters from Letter 53 of April 4, 1687 (AB 98) through Letter 83 of April 4, 1694 (AB 137). Of the 33 letters with scientific observations, 28 of them had a total of 315 figures. Leeuwenhoek published 31 of these letters in Works II.

Period 4 - 1694-1702

The 99 letters from the letter of May 26, 1694 (AB 138) through Letter 146 of April 20, 1702 (AB 236). Of the 73 letters with scientific observations, 35 of them had a total of 194 figures. Leeuwenhoek published 63 of these letters in Works III.

Period 5 - 1702-1712

The 58 letters from the Letter [147] of May 28, 1702 (AB 237) through Letter [190] of June 10, 1712 (AB 294). Of the 49 letters with scientific observations, 29 of them had a total of 244 figures. The letters between Sevende Vervolg and Send-Brieven. Hans Sloane published 44 in Philosophical Transactions.

Period 6 - 1712-1719

The 52 letters from the letter of November 8, 1712 (AB 295) through the letter of November 28, 1717 (AB 346). Of the 46 letters with scientific observations, 22 of them had a total of 144 figures. Leeuwenhoek published all 46 of these letters, what he called Send-Brieven, in Works IV.

Period 7 - 1720-1723

The 18 letters from Letter [XLVII] of January 9, 1720 (AB 347) through the letter of August 1723 (AB 364). Of the 15 letters with scientific observations, 9 of them had a total of 46 figures. The letters after Leeuwenhoek stopped publishing them himself; James Jurin excerpted the 15 letters with scientific observations in Philosophical Transactions.