Lacaille’s Horologium

Lacaille showed Horologium under the name l’Horloge on his original 1756 planisphere. The name was Latinized as Horologium on the second edition of 1763. Lacaille depicted a simple pendulum clock of the type invented by the Dutch scientist Christiaan Huygens in 1656. This illustration comes from a copy of Lacaille’s original planisphere published in the Atlas Céleste of Jean Fortin. (Image © Ian Ridpath.)