Hoover, Herbert and Lou Henry Hoover.
Photo signed by both, 6½ x 10 in., n.p., n.d. A full-length portrait in a wooded environment with an American flag in the background, Both the President and Mrs. Hoover signed on the ground below their feet. Fine. Hoover, a mining engineer, and his wife Lou, a geologist and linguist, translated the 1556 mining classic De re metallica
from the Latin. Their important scholarly version was published in 1912 and is still in print today. Estimated Value $400 - 600