What do you do?

What do you do when you see things that no one has ever seen before?

When you show these things to the people around you, they don't see them. Or they can't see or won't see them.

So then what do you do?

This web explores how a curious, methodical Dutchman responded to just that situation more than three hundred years ago.

17th century tile
made in Delft

Below is a brass magnifying glass aka microscope made by hand by Antony van Leeuwenhoek in the late 1600's. The plate is about 5 cm (2 in) high. It will fit easily into the palm of your hand. The single spherical glass lens is a little more than a millimeter (4/100th's of an inch) in diameter.

This microscope was an order of magnitude better in terms of magnification and resolution than any other microscopes available in the 1600's.

What else is here?

Site Guide

How to use Lens on Leeuwenhoek. Abbreviations, spelling, and other trade-offs and compromises to adapt Leeuwenhoek's messy life to the rigors of the database.


Comprehensive bibliography of printed information, some available online, about Antony van Leeuwenhoek and his times.


Where to find - in the Netherlands and online - the documents and other information used for this web.


Learning the Dutch language, with an emphasis on the 17th century.

Search, Glossary, Index

Find information by search term, content title, and topic.


Who made this web? Why? How? What about copyrights?

Featured page

In the Netherlands today, more than five dozen streets of various types are named after Antony van Leeuwenhoek. Is one near you?

Find out with Willem Reijnders' interactive Google Map: Streets in the Netherlands named after Leeuwenhoek


Antony van Leeuwenhoek

1632 - 1723
Delft, the Dutch Republic

portrait of Antony van Leeuwenhoek

Portrait by Jan Verkolje

What you will find here


The life of Anthony van Leeuwenhoek, cloth merchant and civil servant, citizen of Delft. Portraits of him. His homes and his legacy as well as a timeline of events in his life.


Over six hundred documented events in the history of Delft and the life of Leeuwenhoek and his family, starting in 1246.


Over a hundred close relatives of Leeuwenhoek. Timelines of the documented facts about their lives and property holdings. Featuring the half dozen most influential women in his life. Grouped by family: Leeuwenhoek, de Meij, Swalmius, de Molijn, van den Berch, and Hogenhouck.

Civic career

Leeuwenhoek's education and training. How he supported his family as a merchant, City Court official, and City inspector of liquid imports and exports.

Scientific career

A brief accounting of some of the aspects of Leeuwenhoek's science, his lenses and people who influenced him, other microscopists, philosophers, and members of the Royal Society.


Nearly three hundred letters over fifty years. Divided into seven periods according to how Leeuwenhoek self-published them. How to find your way among the various editions and translations.

Delft in Holland

Life in the heart of the world's most prosperous and learned country. Views and maps, timelines of Delft's history. How Delft was governed and Leeuwenhoek's role in it. The buildings in his neighborhood. His contemporaries. Almost a hundred parcels of property in and around Delft owned by Leeuwenhoek and members of his family. Life in Leeuwenhoek's Holland through the eyes of its painters.

The Curious Observer

Leeuwenhoek wrote about the day he made a startling and unexpected discovery:

In the year 1675, about half-way through September ..., I discovered living creatures in rain, which had stood but a few days in a new tub, that was painted blue within.

This observation provoked me to investigate this water more narrowly; and especially because these little animals were, to my eye, more than ten thousand times smaller than the little animal which Swammerdam has portrayed.

"Living creatures in rain water"? "Ten thousand times smaller"? They had always been there, but no human had ever seen them until that September day almost three hundred and fifty years ago.

  • Who was this man with this chatty writing style about tiny animals?
  • How did he manage to stumble onto this Eden, where he was Adam, surrounded by animals with no names?
  • Why do we remember Antony van Leeuwenhoek today?
  • What can he teach us about how to explore our own worlds?

What do you do when you see things that no one has ever seen before?
Wat doe je als je dingen ziet dat niemand ooit heeft gezien?


Lens on Leeuwenhoek

This web, the online record of an ongoing research project, will continue to grow and develop. Instead of pages organized by chapters, it has a database organized by a taxonomy; its top level is shown in the links across the top.

The author is responsible for accuracy of the information on this web. Corrections are welcome.

Why we remember Leeuwenhoek today

This linen merchant and civil servant from Delft developed a tiny single-lens microscope that let him become the first human to see the hidden world of microorganisms. His fifty years of letters, many to the Royal Society of London, recorded his observations of protozoa, bacteria, spermatozoa, and red blood cells flowing through capillaries, among many other things.


Antony van Leeuwenhoek
and his "Little Animals"

by Clifford Dobell

First published in 1932, but it has not been surpassed. If you read only one biography, make it Dobell's.

Video Overview

of the life, times, and
accomplishments of
Antony van Leeuwenhoek

(< 8 minutes)

What is coming

This web will be developing for a long time because Leeuwenhoek lived such a long life full of interesting accomplishments.

Coming next, his letters and his scientific career:

His Publications

The rest of his nearly three hundred letters over fifty years.

Tiny Lenses

The three methods Leeuwenhoek used to make his lenses: grinding, blowing, and drawing.

Tiny Microscopes

Leeuwenhoek made palm-sized microscopes from brass and silver to hold his tiny lenses and position his specimens.

Using the Microscopes

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

As Science Began

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

Did you know ...?

In the history of the British Royal Society's journal Philosophical Transactions, Leeuwenhoek, with over a hundred and twenty articles, is its most frequently published author, by far.

Leeuwenhoek 122
Martin Lister 87
Edmond Halley 81
Robert Boyle 58