从颜色上看，lead-coated brass ball肯定不对，更有可能是铜壳灌铅。
用纯铅或纯铜，重量28kg的球体对应的直径是16.8cm和18.2cm。
http://www.cleonis.nl/physics/phys256/foucault_pendulum_intro.phpFoucault's third pendulum was build in the Pantheon in Paris. It had a 67 meter wire, and the 16 centimeter diameter bob was a spherical brass shell filled with lead.
(Many sources describe the pendulum bob as 'a cannonball', but that is incorrect.……