Edmond Becquerel. French physicist (1820–1891). Untranslated ALS in French, one page, 5.25 x 8.25, October 8, 1869. In fine condition, with scattered light creasing. Becquerel studied the solar spectrum, magnetism, electricity and optics. He is credited with the discovery of the photovoltaic effect, the operating principle of the solar cell, in 1839. He is also known for his work in luminescence and phosphorescence. He was the son of Antoine César Becquerel and the father of Henri Becquerel, one of the discoverers of radioactivity. RARE.