On a summer day in 1674, in the small Dutch city of Delft, Antoni van Leeuwenhoek--a cloth salesman, local bureaucrat, and self-taught natural philosopher--gazed through a tiny lens set into a brass holder and discovered a never-before imagined world of microscopic life. At the same time, in a nearby attic, the painter Johannes Vermeer was using another optical device, a camera obscura, to experiment with light and create the most luminous pictures...