Viktor Schauberger, Callum Coats (2000). “The Energy Evolution – Harnessing Free Energy from Nature: Volume 4 of Renowned Environmentalist Viktor Schauberger’s Eco-Technology Series”, p.149, Gill & Macmillan Ltd
Viktor Schauberger, Callum Coats (2000). “The Energy Evolution – Harnessing Free Energy from Nature: Volume 4 of Renowned Environmentalist Viktor Schauberger’s Eco-Technology Series”, p.230, Gill & Macmillan Ltd