Schauberger
In order to counter these opposing views practically, test pipes 64 metres long with an internal diameter of 27.5 cm (11 inches) were fabricated. At a gradient of 1%, ore and pebbles with a grain-size of about 10 cm (4 inches) in cross-section were transported down the pipe. The experiments were carried out at Kohlleben. The steeper the geological gradient was, the more efficacious the transport. [The Energy Evolution - Harnessing Free Energy from Nature, The Transport of Ore in Double-Spiral-Flow Pipes]