Clark, Alvan
Clark, Alvan (18041887), a United States maker of astronomical lenses. Five times his firm, Alvan Clark & Sons, made the then-largest telescope lens in the world. The fifth one, completed 10 years after his death, is the 40-inch (102-cm) refractor at the Yerkes Observatory at Williams Bay, Wisconsinstill the world's largest. Clark was born in Ashfield, Massachusetts.