Directions of precision: George Graham's instructions for his pendulum astronomical clocks.

Abstract

In the 1720s two Jesuit astronomers working at the court of King João V of Portugal, in Lisbon, received several instruments produced by the best makers in London, Paris and Rome. With the crucial help of the Portuguese diplomatic network contacts with academies, savants and instrument makers were established, seeking technical advice and the best astronomical instruments available at the time. It was in this context that in April 1726 a set of Latin instructions accompanying pendulum clocks made by George Graham were dispatched from London to Lisbon. These unpublished instructions are now preserved in the papers of Giovanni Battista Carbone, one of these Jesuit astronomers, offering a significant window into the procedures and technical details involved in the setting, operation and transport of Graham's astronomical clocks. In this paper, I will not only discuss this important document in the framework of Graham's contributions to astronomy and horology, but also in the perspective of the search for accuracy.