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.