Introduction

In the mid-1600s, Europe’s population had been decimated by three centuries of bubonic plagues. The deadliest had been the Black Death, killing one-third of the population between 1347 and 1352. Between each epidemic European cities repopulated and rebuilt their commerce. In Amsterdam, the Dutch had ceded dominance of the seas to England but retained a central role in European finance and the trade routes. Glass, textiles, and spices moved by the ton through the Netherlands’ ports.

After apprenticing in Amsterdam, cloth merchant Antoni van Leeuwenhoek returned to his birthplace Delft to start his own business and capitalize on the growing economy. Needing a way to assess fabric quality and compete with established clothiers, van Leeuwenhoek experimented with glass lenses of various thicknesses to magnify individual threads. More than 75 years earlier, eyeglass makers Zacharias Janssen and his father, Hans, had put multiple lenses in sequence to amplify magnification and in doing so invented the first compound microscope. Van Leeuwenhoek used mainly single lenses, but he formed them with precision, enabling him to observe the microscopic world as no one had before.