Empirical Earth · Gravity, Buoyancy & the Air

A mountain that pulled a plumb line sideways

The claim

“‘Down’ is just a fixed universal direction — nothing pulls a plumb line toward mass.”

What is measured

A Scottish mountain pulled a plumb line about 11.6 arcseconds out of true in 1774, proving “down” points toward mass, not along a universal arrow. The same measurement gave Earth’s density (denser than its rocks, so no hollow inside) and, through Hutton’s contour lines, founded geophysics. On why a plumb line marks level and not flat, see flat versus level.

What would show this is wrong

showing a plumb line near a large isolated mountain hangs exactly along the star-defined vertical with no mass-dependent deflection, contrary to the 11.6-arcsecond result.

Sources

  1. The Schiehallion experiment (1774). Nevil Maskelyne measured an ~11.6-arcsecond deflection of a plumb line by the mass of the Scottish mountain Schiehallion, from which Earth’s mean density link
  2. Schiehallion: weighing the Earth. Maskelyne and Hutton found the Earth nearly twice as dense as the surface mountain (ruling out a hollow Earth); Hutton invented contour lines to model the p link
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