Round Hill was the site of early-to-mid 20th century research into the uses of radio and microwaves for aviation and communication by MIT scientists, including physicist Robert J. Van de Graaff. There in 1933 he built the world's largest air-insulated Van de Graaff generator (now located at the Museum of Science (Boston)). It is also the site of the Green Mansion, the estate of "Colonel" Edward Howland Robinson Green, a colorful character who was son of the even more colorful and wildly eccentric Hetty Green, nicknamed the "Witch of Wall Street". Hetty was said to be the richest woman in the world in her time, and is listed in the Guinness Book of Records as the "world's greatest miser."