Oh I forgot to mention my favorite 18th century experiment which used a plumb bob, like on a pendulum, and the gravitational pull of a mountain in Scotland to e

Oh I forgot to mention my favorite 18th century experiment which used a plumb bob, like on a pendulum, and the gravitational pull of a mountain in Scotland to estimate the mass and size of the earth https://en.m.wikipedia.org/wiki/Schiehallion_experiment https://en.m.wikipedia.org/wiki/Schiehallion_experiment Many surveying expeditions had cartographical errors attempting to draw straight lines across vast distances due to this phenomena when they were passing the various because of their gravitational pull. These surveys had to be done at night because they relied on the stars to guide them and used the gravity of the perpendicular plumb to go straight. The pull of the mountains were not accounted for. This has a name https://en.m.wikipedia.org/wiki/Vertical_deflection https://en.m.wikipedia.org/wiki/Vertical_deflection It also disproved Hollow Earth theory, which at the time had a number of notable supporters, such as Edmond Halley, who to go back, was a friend of Newton's and plausibly copied Flamsteed's work on the famous comet. Flamsteed was really protective and didn't like Halley so it's hard to suss out the reality. He made the calculations predicting the return but viewed them as property of the observatory being made during his employment there. Haley, who had access to the work, on the other hand, publicized his calculations and was not protective. Did he independently derive them? Haley claims he didn't know about the work, Flamsteed says otherwise. Who knows? +1 for open access I guess