Browsing through Walten’s notes also helped Jagersma to get to know the pamphleteer better, even though he is been dead for three hundred years. “The Memoriaelen say a lot about him. I could read how Walten did his research, follow his fascinations, and see the ideas for pieces he was not able to work out anymore. In a way, these two notebooks are a kind of self-portrait.”

He also collected facts about all kinds of people, including his enemies. For example, he took note of any gossip about conservative ministers who disagreed with him. He recorded their visits to prostitutes in his Memoriaelen.

In Walten’s two notebooks, referred to as Memoriaelen, Jagersma discovered a lot of details about the pamphleteer’s life. “These notebooks look a bit like the Moleskine notebooks that we know today,” says Jagersma, “but thicker, and bound in parchment.” In the more than five hundred pages, Walten collected all kinds of information. Jagersma lists the categories: “Personal anecdotes, philosophical and theological reflections, ideas, incursions, medical recipes, accounts of alchemical experiments, but also departure and arrival dates of the trekschuit (sail- or horse-drawn boat). The notebooks also contain lists of books he still wanted to read.”

At the National Archives in The Hague, Jagersma was able to recover two documents that historians believed to be lost. These were the notebooks of Ericus Walten. These manuscripts had been confiscated by a court, the High Court of Holland, when Walten was arrested in 1694.