Note 56 — DEVELOPMENT OF GRAVITY PENDULUMS IN THE 19th CENTURY
Reading edition
The pendulums with conical bobs are described and illustrated in E. D. Preston, “Determinations of Gravity and the Magnetic Elements in Connection with the United States Scientific Expedition to the West Coast of Africa, 1889-90,” Report of the Superintendent of the Coast and Geodetic Survey for 1889-90 (Washington, 1891), app. no. 12.