As Science Began

How the self-educated van 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 In 1942, after reading the million words that Newton wrote about alchemy over two decades in until recently unpublished journals and personal notebooks, John Maynard Keynes told the Royal Society Club that "Newton was not the first of the age of reason.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.

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?

Van 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, van 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.

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

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Evidence from observations

Repeatedly in his letters, van 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.

Hooke's best-selling Micrographia was organized as numbered Observations. To him, the new, Bacon-inspired science did not need "strength of Imagination and exactness of Method" or "depth of Contemplation". It needed:

a sincere Hand and a faithful Eye, to examine, and to record, the things themselves as they appear.

To Hooke, accurate observation is itself a desirable form of knowledge. Many articles throughout the early years of Philosophical Transactions have "observations" in the title.

These observations were not always self-evident or easily accomplished. In June 1699, van Leeuwenhoek wrote:

Everyone is not fit to judge well and truly of a Magnifying-glass, much less can he be fit to make new Discoveries, and thus doing so no Body must Publish or bring to light, new Discoveries, and judge by one sight, but he must see the same over and over several times,

for it doth happen often to me, that People looking through a Magnifying-glass, do say now I see this, and then that, and when I gave them better Instructions, they saw themselves mistaken in their opinion,

and what is more, even he that is very well used to look through Magnifying-glasses, may be misled by giving too sudden a Judgment of what he doth see.

Evidence from experiments

Van Leeuwenhoek also described experiments, that is, things he did to answer his next question: what if?

In his third letter (illustration on left) to Henry Oldenburg, April 7, 1674, van Leeuwenhoek writes about an experiment he made to test his hypothesis that, because there are no vacuums, air cannot be compressed either. Minute particles, "the first and finest matter of Air", must be passing through the walls of whatever chamber contained the air. To test this, he tried to press particles through glass.

It didn't work (explanation on left).

But what motion soever I make with the forcer, and press out the Air , the water at the small hole keeps its station.

But the experiment raised new questions.

And yet, if I do but apply my warm hand to the exterior pipe, the water presently flies out. This puzzles me; nor can I find a satisfactory reason for this Phenomenon.

As van Leeuwenhoek kept gaining experience and expertise, his experiments became more sophisticated. His long series of experiments with various water infusions culminated in the long letter of October 9, 1676: "Observations concerning various little Animals, in great numbers discover'd by Mr. Leewenhoeck in Rain- Well- Sea- and Snow-water; as also in water wherein Pepper had lain infused."

Henry Oldenburg published it the following March in Number 133, just ahead of the article reprinted from France's Journal des Scavans by Giovanni Cassini announcing his discovery of the two "planets" around Saturn.

The next number, the next month, Oldenburg published van Leeuwenhoek's equally important letter of March 23, 1677: "Monsieur Leewenhoecks Letter giving some account of the manner of his observing so great a number of live Insects in several sorts of water".

While van Leeuwenhoek's procedures can be seen as lacking according to modern scientific standards, a reading of other articles in Philosophical Transactions shows that his experiments were as controlled and documented as those of his peers.

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Validity of process

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 van 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.

The founders of the Royal Society in 1660 were putting into action the ideas in Bacon's Novum Organum (1620) and New Atlantis (1627). Bacon said that the philosopher, what we now call the scientist, should abandon Aristotle's method. Instead, to discover cause and effect in nature, the scientist should proceed through inductive reasoning from fact of nature to law of nature.

Something observed by one person was more likely to be really there if another person at another time and place could observe it, too.

In Discourse on Method (1637), Descartes presented the four precepts that characterize his method. The precepts are on the left, and van Leeuwenhoek's adherence to them is discussed on the No Longer Any Doubt page. They were very influential among the "natural philosophers" who were gathering regularly in London and Paris, outside the universities, to explore the implications of these new methods.

The Royal Society's Henry Oldenburg was the founding editor of its journal, Philosophical Transactions, that made a point of publishing observers and experimenters who followed these new, radical philosophies. Right away, he recognized that van Leeuwenhoek was among them.

Philosophical Transactions's thousands of pages are filled with descriptions of things from all over the world by people from all over the world. In the sky, they tracked and measured everything they could see with a telescope. Here on earth, they counted chimneys and they opened cadavers. With a microscope, they looked closely at fleas and leaves, things they could already see.

According to Descartes' first precept, it was very important that the things they discovered were true. These moons and planets, cells and animalcules, had to really be there. They had to be doing what their discoverers claimed they were doing. In other words, they had to be valid.

When Nehemiah Grew and Robert Hooke had trouble repeating van Leeuwenhoek's results, that is, had trouble demonstrating their validity, van Leeuwenhoek's response was to resort to experts. Birch's History notes that during the Royal Society's meeting of November 1, 1677:

Mr. LEEWENHOECK'S papers ... were read; four of which were testimonials of two ministers, a public notary, and other persons of good credit to the number of eight, of the truth of his former assertions concerning the almost incredible number of small animals wriggling in pepper-water; some of whom estimated, that they saw ten thousand, others thirty thousand, others forty-five thousand little animals in a single drop of water as big as a millet-seed.

However, that was not enough. The days of establishing validity by the witness of credible learned men were over. Van Leeuwenhoek was the first to admit that his claims about so many tiny animals were unbelievable. His observations would not be considered valid because ministers and notaries testified to their truth. The results had to be reliable, replicable, in order to be valid.

Early in his career, van Leeuwenhoek tried to replicate the findings of Jan Swammerdam and Christiaan Huygens. Later, his showcase experiment for visitors was a validation of Harvey's theory about circulation of the blood. Toward the end of his career, he tested the ideas of Herman Boerhaave, professor in nearby Leiden.

In England, one of the main purposes of the Royal Society's meetings was to validate other scientists' results. The members would watch their curator of experiments, Robert Hooke, sometimes with help, perform experiments. Birch's History of the Royal Society is almost solely the notes and journals of these weekly meetings. Hooke's recently recovered Folio fills in a few gaps. The story of how the members went about replicating Leeuwenhoek's results is scattered over many meetings, the notes of which are often brief or incomplete.

The story on the "No Longer Any Doubt" page -- how the Royal Society came to validate van Leeuwenhoek's observations -- shows the new ideas at work.

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Peer Review

Four hundred years ago, when the world of science was so new, it was quite possible for learned societies and the "virtuosi" who belonged to them to keep up with everything. In other words, there was so little depth in the 1600's that breadth was still possible.

From Birch's History, we can see the breadth. During the November 1677 meetings when Hooke struggled with replicating van Leeuwenhoek's results, the members of the Society also discussed

sulfur water
imitation leather from salad oil and wax
comparing weights of liquids to the hundred thousandth part
preserving wine
reproduction in carp, lobsters, silkworms, and chickens
the structure of palmetto trees

Volume 12 of their journal had articles on an equally broad variety of topics, as shown on the list below left. Van Leeuwenhoek's contributions to volume 12 are listed below right.

Volume 12 also included an "Extract of a Letter form Mr. Butterfield Mathematique Instrument-maker to the French King, about the making of Microscopes with very small and single Glasses" (.pdf) giving instructions for making a microscope just like van Leeuwenhoek's. See excerpt below left.

In today's world of hyper-specialization, competitive public funding, and thousands of journals, peer review differs from peer review in the world of the Royal Society four hundred years ago. Only France had similar institutions, the Academie Francais and its Journal des Scavans. Each of these journals translated and re-printed articles from the other.

Where now a journal editor spreads the risk by asking experts to make anonymous and independent assessments of all submitted articles, back then the editor of Philosophical Transactions made those decisions himself.

While Hooke's validation of claims was peer review, today we ask peers only to read the report, not replicate the results. In addition, there was not a clear distinction between letters to the Society and submissions to its journal, both of which were sometimes read aloud and less often discussed, which is another sort of peer review.

In the unsettled decade after Oldenburg's death in 1677, the members tried to use a paid editor supervised by the secretaries, but that didn't work well. As detailed in the Letters pages, Edmond Halley was that editor, he had other projects more demanding of his time, and in any case, he was paid with copies of a book that the Society had printed but had not been able to sell.

Then, as now, peer review by independent experts is only the first gate to pass through. Then there is the editor. As detailed on the Period 4 and Period 6 pages, Halley, an astronomer, published articles by his fellow astronomers and mathematicians rather than biologist and botanists or the microbiologist van Leeuwenhoek.

Van Leeuwenhoek's response, in a world in which Philosophical Transactions was the only alternative, was to publish his own letters by hiring a printer. Yes, that's self-publication and not peer-reviewed. But what about Halley? After van Leeuwenhoek and Martin Lister, Halley had the third highest total number of articles published in Philosophical Transactions, 81. Yet a third of them he published while he was editor (13 in vol 16, 8 in v 29 and 5 in v 30), with himself as the only peer reviewer. Van Leeuwenhoek did not pretend otherwise when he published himself. Yet at the whim of half-a-dozen different editors, he still managed to have half again as many articles published in Philosophical Transactions as Halley did.

So then, who were van Leeuwenhoek's peers? Halley, the astronomer? Others used magnifying lenses, but they turned them to the planets, stars, and comets. Others examined plants and animal structures and tissues, but without powerful microscopes.

In 1692, Robert Hooke wrote:

the Fate of microscopes, as to their Inventions, Improvements, Use, Neglect and Slighting, ... are now reduced almost to a single votary, which is Mr. Leeuwenhoek; besides whom, I hear of none that make any other Use of that Instrument, but for Diversion and Pastime.

If the point of peer review is to minimize the erroneous, van Leeuwenhoek was more than receptive to the idea. He actively and repeatedly sought it out, especially during the mid- and late-1670's when his letters began to make more extraordinary, incredible claims and Oldenburg was not publishing them. (See ""No Longer Any Doubt" page.)

Halfway through his career, as it turned out, he wrote to his editor Hans Sloane on Christmas Day, 1700 (Dobell translation):

As I aim at nothing but Truth, and, so far as in me lieth, to point out Mistakes that may have crept into certain Matters; I hope that in so doing those I chance to censure will not take it ill: and if they would expose any Errors in my own Discoveries, I'd esteem it a Service; all the more, because 'twould thereby give me encouragement towards the attaining of a nicer Accuracy.

In van Leeuwenhoek's time, peer review was a new idea, developing toward what it is today. But van Leeuwenhoek recognized its value and was an eager participant.

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Open publication

Fortunately, van 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.

There was another motive for Oldenburg when he established Philosophical Transactions. Until then, the main means of scientific communication was the learned letter copied and passed by mail through networks of interested people throughout Europe.

In this intense social network, there was much opportunity for disputes about priority of discovery. Philosophical Transactions, with print runs early on in excess of a thousand copies, distributed dated, exact copies of these learned letters all over Europe.

According to Bishop Sprat's 1667 History of the Royal Society, members of this new society spurned:

amplifications, digressions, and swellings of style ... bringing all things as near the Mathematical plainness, as they can: and preferring the language of Artizans, Countrymen, and Merchants, before that, of Wits and Scholars.

For van Leeuwenhoek, the English versions of his letters in Philosophical Transactions and translations from English into French for the Journal des Scavans was not enough. Van Leeuwenhoek published 165 of his own letters in parallel Dutch and Latin versions. They were printed in Leiden and Delft and most of them were never published elsewhere during his lifetime. (See the Publications page.)

He made no attempt to trim, rearrange, or otherwise systematize his work beyond rough chronological groupings and freshly engraved illustrations. However, he felt strongly that revealing his observations and the results of his experiments was worthwhile. In that same letter of June 12, 1716, van Leeuwenhoek wrote:

My work, which I've done for a long time, was not pursued in order to gain the praise I now enjoy, but chiefly from a craving after knowledge, which I notice resides in me more than in most other men.

Collected, his hundreds of letters run to hundreds of thousand of words, plus hundreds of illustrations, each published in two or three languages, many of them in the most prestigious journal of the time, and distributed as widely as possible. He had, of course, a long life and a constant output, but van Leeuwenhoek nevertheless out-published most of his peers, just in terms of quantity.

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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 equipment is complex and expensive, trained researchers are rare and expensive, and massive amounts of data are often processed over long periods of time. Accountability to funding organizations is time-consuming and expensive.

Four hundred years ago, however, conditions were very different. As Hooke showed with his wide array of clever, creative experiments, the equipment can be hand-made, the researchers can train themselves, and the data can be processed with pencil, paper, and arithmetic. Looking at the incomplete, messy record of the early Royal Society supplemented by Hooke's newly found Folio, we can see that accountability even then met the natural resistance of the creative human mind to pay attention to the recent past; the immediate future is too interesting.

The idea here is that the group as a whole is smarter than any individual. The group has more and better information, as a whole, and will tend to make better decisions. Scientists who work together benefit from a group creativity during the process compared to the benefit that they get from journal articles that are always lagging the research, often by years because of time-consuming peer review.

Van Leeuwenhoek stayed in Delft, wisely preserving his independence and autonomy. But he corresponded with people in several different countries about his research interests, and many people visited him. As documented by his letters on the No Longer Any Doubt page, he offered criticism and responded to criticism by his neighbors and skeptics as well as by some of the leading minds of his day. He was a proud Fellow of the most prestigious society of experts and the most frequent contributor to their journal.

While van Leeuwenhoek worked alone, he did not think alone.

Conclusion

You will often read that van Leeuwenhoek is not considered among the first rank of scientists because he was an "amateur". He did not have the mind of a theoretician like Newton.

But neither did anyone else at the time. No one was able to synthesis and theorize about the evidence presented in van Leeuwenhoek's voluminous observations. As one example, it took almost another two centuries for van Leeuwenhoek's little animals "prettily a-swimming" to turn into threatening germs in the wake of the discoveries of Louis Pasteur, Joseph Lister, and Robert Koch.

On the contrary, it seems to me, van Leeuwenhoek was as much a scientist as anyone of his time. He held and practiced the values of empiricism, objectivity, and openness. He willingly participated in the validation of his claims. He was for half a century an important participant in what we now call the Scientific Revolution and the Enlightenment.