Francis Birch | |
|---|---|
 Birch,c. 1970 | |
| Born | (1903-08-22)August 22, 1903 |
| Died | 30 January 1992(1992-01-30) (aged 88) |
| Alma mater | Harvard University |
| Known for | Birch's law Birch-Murnaghan equation of state |
| Spouse | Barbara Channing |
| Awards | Legion of Merit (1945) Arthur L. Day Medal (1950) William Bowie Medal (1960) National Medal of Science (1967) Vetlesen Prize (1968) Penrose Medal (1969) Gold Medal of the Royal Astronomical Society (1973) |
| Scientific career | |
| Fields | Geophysics |
| Institutions | Harvard University |
| Doctoral advisor | Percy Bridgman |
| Signature | |
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Albert Francis Birch (August 22, 1903 – January 30, 1992) was anAmericangeophysicist. He is considered one of the founders of solid Earthgeophysics. He is also known for his part in theatomic bombing of Hiroshima and Nagasaki.
DuringWorld War II, Birch participated in theManhattan Project, working on the design and development of thegun-type nuclear weapon known asLittle Boy. He oversaw its manufacture, and went toTinian to supervise its assembly and loading intoEnola Gay, theBoeing B-29 Superfortress tasked with dropping the bomb.
A graduate ofHarvard University, Birch began working ongeophysics 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, andprofessor emeritus in 1974.
Birch published over 100 papers. He developed what is now known as theBirch-Murnaghan equation of state in 1947. In 1952 he demonstrated that Earth'smantle is chiefly composed ofsilicate minerals, with aninner andouter core of molteniron. In two 1961 papers oncompressional wave velocities, he established what is now calledBirch's law.
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 atSt. 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, andWestern High School, where he joined theHigh School Cadets in 1916.[1][2]
In 1920 Birch enteredHarvard University on a scholarship. While there he served in Harvard'sReserve Officers' Training Corps Field Artillery Battalion. He graduatedmagna cum laude in 1924, and received hisBachelor of Science (S.B.) degree inelectrical engineering.[1]
Birch went to work in the Engineering Department of theNew York Telephone Company. He applied for and received anAmerican Field Service Fellowship in 1926, which he used to travel toStrasbourg, and study at theUniversity of Strasbourg's Institut de Physique under the tutelage ofPierre Weiss.[3] There, he wrote or co-wrote four papers, in French, on topics such as theparamagnetic properties ofpotassium cyanide, and themagnetic moment of Cu++ ions.[4]
On returning to the United States in 1928, Birch went back to Harvard to pursue physics. He was awarded hisMaster of Arts (A.M.) degree in 1929, and then commenced work on his 1932Doctor of Philosophy (Ph.D.) degree under the supervision ofPercy Bridgman,[3] who would receive theNobel Prize for Physics in 1946. For his thesis, Birch measured thevapor-liquid critical point ofmercury. He determined this as 1460±20 °C and 1640±50 kg/cm2, results he published in 1932 in thePhysical Review.[4][5]
Around this time, there was an increased interest in geophysics at Harvard University, andReginald Aldworth Daly established a Committee for Experimental Geology and Geophysics that included Bridgman, astronomerHarlow Shapley, geologistsLouis Caryl Graton and D. H. McLaughlin and chemist G. P. Baxter.William Zisman, another one of Bridgman's Ph.D. students, was hired as the committee's research associate, but, having little interest in the study of rocks, he resigned in 1932. The position was then offered to Birch, who had little interest or experience in geology either, but with the advent of theGreat Depression, jobs were hard to find, and he accepted.[6][7]
On July 15, 1933, Birch married Barbara Channing, aBryn Mawr College alumna, and acollateral descendant of the theologianWilliam Ellery Channing. They had three children: Anne Campaspe, Francis (Frank) Sylvanus and Mary Narcissa. Frank later became a professor of geophysics at theUniversity of New Hampshire.[8][9]
In 1942, duringWorld War II, Birch took a leave of absence from Harvard, in order to work at theMassachusetts Institute of TechnologyRadiation Laboratory, which was developingradar. He worked on theproximity fuze, a radar-triggered fuze that would explode a shell in the proximity of a target. The following year he accepted a commission in the United States Navy as alieutenant commander, and was posted to theBureau of Ships in Washington, D.C.[10]
Later that year he was assigned to theManhattan Project, and moved with his family toLos Alamos, New Mexico. There he joined theLos Alamos Laboratory's Ordnance (O) Division, which was under the command of another Naval officer,CaptainWilliam S. Parsons. Initially the goal of the O Division was to design agun-type nuclear weapon known asThin Man. This proved to be impractical due to contamination of the reactor-bredplutonium withplutonium-240, and in February 1944, the Division switched its attention to the development of theLittle Boy, a smaller device usinguranium-235. Birch used unenriched uranium to create scale models and later full-scale mock-ups of the device.[11]
Birch supervised the manufacture of the Little Boy, and went to Tinian to supervise its assembly and loading it ontoEnola Gay, theBoeing B-29 Superfortress tasked with dropping the bomb. He devised the 'double plug' system that allowed for actually arming the bomb afterEnola Gay took off so that if it crashed, there would not be a nuclear explosion.[11] He was awarded theLegion of Merit. His citation read:
for exceptionally meritorious conduct in the performance of outstanding services to the Government of the United States in connection with the development of the greatest military weapon of all time, the atomic bomb. His initial assignment was the instrumentation of laboratory and field tests. He carried out this assignment in such outstanding fashion that he was placed in charge of the engineering and development of the first atomic bomb. He carried out this assignment with outstanding judgment and skill, and finally, went with the bomb to the advanced base where he insured, by his care and leadership, that the bomb was adequately prepared in every respect. Commander Birch's engineering ability, understanding of all principles involved, professional skill and devotion to duty throughout the development and delivery of the atomic bomb were outstanding and were in keeping with the highest traditions of the United States Naval Service.[12]
Birch was promoted to commander and released from the Navy in 1945.[13]
Birch returned to Harvard after the war ended, having been promoted to associate professor of geology in 1943 while he was away. He would remain at Harvard for the rest of his career, becoming a professor in 1946, and Sturgis Hooper Professor of Geology in 1949, andprofessor emeritus in 1974. Professor Birch published over 100 papers.[2][3] He served as president ofThe Geological Society of America in 1964 and was awarded theirPenrose Medal in 1969.[14]
In 1947, he adapted the isothermal Murnaghan equation of state, which had been developed for infinitesimal strain, forEulerian finite strain, developing what is now known as theBirch-Murnaghan equation of state.[15]
Albert Francis Birch is known for his experimental work on the properties of Earth-formingminerals at high pressure and temperature, in 1952 he published a well-known paper in theJournal of Geophysical Research, where he demonstrated that themantle is chiefly composed ofsilicate minerals, the upper and lower mantle are separated by a thin transition zone associated with silicatephase transitions, and theinner andouter core are alloys of crystalline and molteniron. His conclusions are still accepted as correct today. The most famous portion of the paper, however, is a humorous footnote he included in the introduction:[16]: 234
Unwary readers should take warning that ordinary language undergoes modification to a high-pressure form when applied to the interior of the Earth. A few examples of equivalents follow:
High Pressure Form Ordinary Meaning Certain Dubious Undoubtedly Perhaps Positive proof Vague suggestion Unanswerable argument Trivial objection Pure iron Uncertain mixture of all the elements
In 1961, Birch published two papers oncompressional wave velocities establishing a linear relation of the compressional wave velocity Vp of rocks and minerals of a constant averageatomic weight with density as:[17][18]
This relationship became known asBirch's law. Birch was elected to theAmerican Academy of Arts and Sciences in 1942,[19] theNational Academy of Sciences in 1950,[20] theAmerican Philosophical Society in 1955,[21] and served as the president of theGeological Society of America in 1963 and 1964.[3] He received numerous honors in his career, including the Geological Society of America'sArthur L. Day Medal on 1950 andPenrose Medal in 1969, theAmerican Geophysical Union'sWilliam Bowie Medal in 1960, theNational Medal of Science from PresidentLyndon Johnson in 1967, theVetlesen Prize (shared with SirEdward Bullard) in 1968, theGold Medal of the Royal Astronomical Society in 1973, and the International Association for the Advancement of High Pressure Research'sBridgman Award in 1983.[22] Since 1992, the American Geophysical Union'sTectonophysics section has sponsored aFrancis Birch Lecture, given at its annual meeting by a noted researcher in this field.[23]
Birch died ofprostate cancer at his home inCambridge, Massachusetts, on January 30, 1992. He was survived by wife Barbara, his three children and his three brothers.[2][20] His papers are in the Harvard University Archives.[3]
