Retrieved 28 August 2009. ↑ "This page has moved". www.museumofhoaxes.com. Retrieved 11 April 2018. ↑ Information originally at www.skepticfiles.org/skep2/pmotion2.htm ↑ "No. 438: Redheffer's PMM-I". www.uh.edu. Retrieved 11 April 2018. ↑ "Perpetual Motion".