John Lyon Burnside III (November 2, 1916 – September 14, 2008) was an American inventor and gay rights activist, known for inventing the teleidoscope, darkfield kaleidoscope, and the Symmetricon. Because he rediscovered the math behind kaleidoscope optics, makers of optically correct kaleidoscopes sold in the United States paid him royalties for decades. Burnside was the life partner of Harry Hay from 1962 until Hay's death in 2002. Burnside was living in San Francisco, at the time of his death on September 14, 2008, from complications of brain cancer.