Nicolas Fatio de Duillier

The man who lit the fuse on the calculus war — and later became a street-corner prophet.

The relationship with Newton

Fatio was a young Swiss mathematician who arrived in London in 1687 and quickly impressed the Royal Society. He met Newton in 1689, and for the next four years the two had the most intense personal relationship of Newton’s life. They exchanged long, emotional letters. Fatio visited Newton in Cambridge for extended stays. Newton offered to set him up with an allowance so they could live near each other.

The nature of the relationship has been debated for centuries. At minimum, Newton — who kept nearly everyone at arm’s length — let Fatio in closer than anyone else, before or after. The relationship cooled abruptly around 1693, coinciding with Newton’s mysterious nervous breakdown.

Triggering the priority dispute

In 1699, Fatio published a paper claiming Newton was the sole inventor of calculus and implying Leibniz had stolen the idea. Leibniz was furious. The Royal Society’s investigation (stacked with Newton’s allies) sided with Newton. The resulting priority dispute consumed both men’s later lives and split European mathematics into hostile camps for a century. Fatio threw the first punch, but Newton was happy to let him.

The prophet phase

In 1707, Fatio joined the Camisards — French Protestant refugees who practiced ecstatic prophecy in the streets of London. He was arrested, convicted, and sentenced to the pillory. Newton, by then Master of the Mint and a public figure, did nothing to help. The brilliant young mathematician who’d once been Newton’s closest companion spent his last decades in obscurity.

In the novel

Fatio appears in the later sections of the Baroque Cycle. His trajectory — from mathematical brilliance to mystical enthusiasm — mirrors the book’s central tension between rational philosophy and older ways of understanding the world.