Representing the Earth's Shape: The Polemics Surrounding Maupertuis's Expedition to Lapland

Abstract

HISTORICAL ACCOUNTS OF QUANTIFICATION in the physical sciences in the eighteenth century have often been described as a straightforward series of steps in a process of maturation, as instruments and standards advanced in precision.' This paper calls into question the self-evident nature of precision by investigating the production and uses of measurements. In the case of the dispute over the shape of the earth, centered in Paris in the 1730s, the precision of measurements was a matter to be interpreted, attacked, defended, and represented. The whole messy business, undertaken by the participants to win consensus from their contemporaries, took place in the context of academic politics and the intellectual fashions of the salons and the court. All parties to the dispute claimed to be drawing on precision measurements; evaluating precision turned out to require the use of a range of intellectual, mathematical, instrumental, political, and textual resources. The alleged precision was then used to construct and defend rival scientific programs and practices. The origins of the eighteenth-century dispute go back to Isaac Newton and Christiaan Huygens, both of whom calculated the earth to be slightly flattened at the poles, though they were working from different theories of gravity. The only empirical support available to them came from pendulum measurements taken near the equator that showed the effect of gravity to be less there than at higher latitudes. By the early eighteenth century French astronomers had produced another set of data: measurements of celestial arcs and terrestrial distances made in the course of an ambitious project to map the kingdom of France. In 1718 Jacques Cassini announced that these measurements implied an elongated rather than a flattened earth. Virtually uncontested for fifteen years, his claim attracted renewed attention in the early 1730s, when a contingent of Paris Academy mathematicians questioned the adequacy of local measures for settling the matter.2 As a result, the royal treasury financed two expeditions, one to the equator and one to the arctic circle, to make measurements for a more definitive comparison.