Loch Tay is a freshwater loch in the central highlands of Scotland, in the Perth and Kinross and Stirling council areas. It is the largest body of fresh water in Perth and Kinross, and the sixth largest loch in Scotland. The watershed of Loch Tay traditionally formed the historic province of Breadalbane. Schiehallion is a prominent cone-shaped mountain of the Breadalbane in Perthshire, Scotland. Schiehallion has a rich botanical life, interesting archaeology, and a unique place in scientific history for an 18th-century experiment in "weighing the world".The Schiehallion experiment was an attempt to measure the mass of the earth using a pendulum and a mountain (Mount Schiehallion). The mass of the mountain was approximated and the deflection of a pendulum due to the gravitational force of the mountain was measured.