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Session 1 - HAD I: LeRoy E. Doggett Memorial Session.
Oral session, Tuesday, January 06

[1.01] Bradley and Lacaille: Praxis as Passionate Pursuit of Exact Science

C. A. Wilson (St. John's College)

From 1700 to 1800, astronomical observation and prediction improved in accuracy by an order of magnitude or more: by century's end astronomers could trust catalogued and predicted positions to within a few arcseconds. Crucial to this improvement were the discoveries of Bradley, which grew out of an endeavor of "normal science," the attempt to confirm with precision Robert Hooke's earlier supposed discovery of annual parallax in Gamma Draconis. On the theoretical side, Bradley's discoveries led to the quiet demise of two earlier doctrines, the Tychonic System and the Aristotelian and Cartesian doctrine of the instantaneous transmissione of light. On the side of praxis, Bradley's discoveries meant that observational astronomy must be re-done from the ground up. In 1742 Nicolas-Louis Lacaille (1713-62), who had been admitted to the Paris Academie des Sciences only the year before, proposed to his astronomer colleagues that they take up this task as a cooperative enterprise. His proposal met with silence, but he undertook the project on his own, making it his life's work. By 1757 he had completed his Fundamenta Astronomiae, including a catalogue of 400 bright stars in which for the first time star positions were corrected for aberration and nutation. In 1758 he published his solar tables, the first to incorporate lunar and planetary perturbations as well as aberration and nutation. Lacaille's pendulum clock was not temperature-compensated, and his sextant poorly calibrated, but he was to some extent able to compensate for these flaws by bringing a massive number of observations to bear. Till the 1790s his Fundamenta Astronomiae and Tabulae Solares were important for the increments in accuracy they brought about, and for the inspiration they gave to later astronomers such as Delambre.

Program listing for Tuesday