Notes of a conversation in Holland with Christian Huygens, concerning an 'horologium' to show hours, months, years, and planetary positions. More general mention of the work of numerous other scientists: Notably, Huygens disputes the notion of John Bernoulli (James Bernoulli's younger brother) that the curve of an inflated sail is part-catenary and part-circle, and warns that Newton ought not to be 'deflected' into theology or chemistry.

Remarks en passant about library volumes in history and physics seen in Leiden. A longer passage follows: notes to a conversation with Christiaan Huygens, critiquing Sir Isaac Newton's notions of absolute motion and the propagation of light. Huygens also says that John Flamsteed ought to declare for the absolute speed of light, and that this should persuade Jean Dominique Cassini.