Adams, William Grylls, (1836-1915) was an English professor of Natural Philosophy at King’s College, London. He discovered that a solid material known as selenium produced electricity when exposed to light. This became known as the photoelectric effect, which the German physicist Heinrich Hertz demonstrated experimentally in 1887. Although selenium solar cells had low efficiencies and would be replaced with silicon cells, Adams’ work proved that a solid material could change light into electricity without heat or without moving parts.