Before 1670, the biological world ended at the edge of what the eye could see.

Soil was dirt. Water was water. Decay was a mystery. The invisible processes that drove fermentation, disease, decomposition, and soil fertility had no names because they had no faces.

Then a draper in Delft ground a lens.

Who Leeuwenhoek Was

Antonie van Leeuwenhoek was not a scientist by training.

He was a cloth merchant in Delft, in what is now the Netherlands. He had no university education. He read no Latin — the language of science in his era. He worked in a shop.

What he had was curiosity and extraordinary manual skill.

He had learned to use magnifying lenses to examine the quality of cloth. He began grinding his own lenses — not with the techniques of others, but with methods he developed himself, largely in secret. His lenses achieved magnifications that...