Fun fact. Charles Mason and Jeremiah Dixon, using theodolites, plumb bobs, and spirit levels, were able to detect variations in gravity from the local environment in 1767. Upon completing the resurvey on the way back to Philadelphia, they noticed a systematic error and concluded it was because of gravitational deflection due to the Allegheny mountains (with the help of Maskelyne, Cavendish and the Royal Society).

Sometimes I think about that and it just blows me away.