Note 81 — DEVELOPMENT OF GRAVITY PENDULUMS IN THE 19th CENTURY

Commandant C. Defforges, “Sur l’Intensité absolue de la pesanteur,” Journal de Physique (1888), vol. 17, pp. 239, 347, 455. See also, Defforges, “Observations du pendule,” Mémorial du Dépôt général de la Guerre (Paris, 1894), vol. 15. In the latter work, Defforges described a pendulum “reversible inversable,” which he declared to be truly invariable and therefore appropriate for relative determinations. The knives remained fixed to the pendulums, and the effect of interchanging knives was obtained by interchanging weights within the pendulum tube.