Francis Birch (August 22, 1903 – January 30, 1992) was an American geophysicist. He is considered one of the founders of solid Earth geophysics. He is also known for his part in the atomic bombing of Hiroshima and Nagasaki. During World War II, Birch participated in the Manhattan Project, working on the design and development of the gun-type nuclear weapon known as Little Boy. He oversaw its manufacture, and went to Tinian to supervise its assembly and loading into Enola Gay, the Boeing B-29 Superfortress tasked with dropping the bomb. A graduate of Harvard University, Birch began working on geophysics as a research assistant. He subsequently spent his entire career at Harvard working in the field, becoming an Associate Professor of Geology in 1943, a professor in 1946, and Sturgis Hooper Professor of Geology in 1949, and professor emeritus in 1974. Birch published over 100 papers. He developed what is now known as the Birch-Murnaghan equation of state in 1947. In 1952 he demonstrated that Earth's mantle is chiefly composed of silicate minerals, with an inner and outer core of molten iron. In two 1961 papers on compressional wave velocities, he established what is now called Birch's law. Early life Albert Francis Birch was born in Washington, D.C., on August 22, 1903, the son of George Albert Birch, who was involved in banking and real estate, and Mary Hemmick Birch, a church choir singer and soloist at St. Matthew's Cathedral in Washington, D.C. He had three younger brothers: David, who became a banker; John, who became a diplomat; and Robert, who became a songwriter. He was educated at Washington, D.C., schools, and Western High School, where he joined the High School Cadets in 1916. In 1920 Birch entered Harvard University on a scholarship. While there he served in Harvard's Reserve Officers' Training Corps Field Artillery Battalion. He graduated magna cum laude in 1924, and received his Bachelor of Science (S.B.) degree in electrical engineering. Birch went to work in the Engineering Department of the New York Telephone Company. He applied for and received an American Field Service Fellowship in 1926, which he used to travel to Strasbourg, and study at the University of Strasbourg's Institut de Physique under the tutelage of Pierre Weiss. There, he wrote or co-wrote four papers, in French, on topics such as the paramagnetic properties of potassium cyanide, and the magnetic moment of Cu++ ions. On