John van Vleck

John Hasbrouck van Vleck was born on March 13, 1899 in Middletown, Connecticut. Both his father and grandfather were university professors. Van Vleck, an only child, moved with his parents to Wisconsin when he was seven when his father became a professor at the University of Wisconsin. He was educated in the Madison, Wisconsin public schools and went on to the University of Wisconsin, where he played in the band. His undergraduate education included courses on railroads and French literature, in addition to physics. Although not an athlete, he was a fan of American football, remembering the scores of games years after they had been played. He graduated in 1920 with a degree in physics. He entered the graduate program at Harvard University and graduated with a Ph.D. in 1922 completing a thesis on the binding energy of a helium atom.

After his doctorate he stayed at Harvard for a year teaching, before taking a job at the University of Minnesota, where he taught graduate physics courses from 1923-1928 He returned to teach at his alma mater, the University of Wisconsin from 1928-1934 and he taught at Harvard from 1934-1969. During World War II he worked on radar at the MIT Radiation Laboratory and participated in the Manhattan Project as part of a committee, with J. Robert Oppenheimer, that studied the feasibility of and designed the first atomic bombs. He also served on the Los Alamos Review Committee, which designed the firing mechanism for "Little Boy", the first atomic bomb used on Hiroshima, Japan.

Van Vleck's early research delt with diamagnetic and paramagnetic materials, and how their behavior could be understood when the new (at the time) field of quantum mechanics was applied. Paramagnetic materials, when exposed to an external magnetic field, are attracted to it, diamagnetic materials are slightly repelled. Neither of the materials retain a magnetic field when the external field is removed. The reason for these behaviors is the electron structures of the different materials, paramagnetic materials have unpaired electrons and diamagnetic do not. Van Vleck also worked on crystal field theory, a branch of chemistry that has to do with the complexes formed by transition metals. He showed that ligands (the atoms or groups of atoms that bond to transition metals) form covalent bonds, not just ionic bonds, with the central metal atom.

In 1977 van Vleck, along with Philip Anderson and Sir Nevil Mott, was awarded the Nobel Prize for Physics "for their fundamental theoretical investigations of the electronic structure of magnetic and disordered systems". Other awards won by van Vleck include the National Medal of Science in 1966 and the Lorentz Medal from the Royal Netherlands Academy of Arts and Sciences in 1974.

Van Vleck retired in 1969 and died in his Cambridge, Massachusetts home on October, 27 1980.


References:

Anderson, P.W.; "John Hasbrouk Van Vleck"; in Biographical Memoirs Vol. 56; National Academy Press; 1987

Carey, Charles W.; American Scientists; Infobase Publishing; 2006

John H. Van Vleck Nobel Autobiography

John Hasbrouck Van Veck Wikipedia Entry

Joseph von Fraunhofer

Joseph von Fraunhofer was born on March 6, 1887 in Straubing, Bavaria. He was the youngest of eleven children of a poor glazier. As soon as he was of age, he began an apprenticeship under his father. His mother died when he was ten and his father when he was eleven, leaving him an orphan. Leaving his home he became the apprentice of Philipp Anton Weichelsberger, the court mirror and glass maker. Weicheslberger was a harsh master and did not allow young Fraunhofer time to study and read.

In 1801 the building that Fraunhofer and Weicheslberger were working in collapsed and both were rescued alive. The future king, Maximilliam Joseph IV was among the rescuers and helped the young man out giving him some money and appointing Joseph von Utzschneider to oversee his apprenticeship, allowing Fraunhofer books and study time. Fraunhofer tired of his apprenticeship and after writing Utzschnider he was offered a position at the Optical Institute at Benediktbeuern, this was a Benedictine monastery that had been converted into a research institute. Fraunhofer worked there, inventing ways to make the world's finest optical glass, surpassing the glass made in England. In 1818 he became the director of the institute.

In 1814 Franhofer invented the spectroscope allowing him to observe the spectral lines of the sun. Fraunhofer measured 574 dark lines in the sun's spectrum. Although these lines had been discovered earlier by William Hyde Wallaston, they are now known as Fraunhofer lines. Fraunhofer used his spectroscope to examine the emission spectrum of many elements and saw that they each had a unique spectrum. Fraunhofer also invented the diffraction grating, a series of thin lines on a lens, that causes a light source to be dispersed into its spectrum.

The dark lines Fraunhofer observed in the sun's spectrum are caused by the light absorbed by the outer layer of the sun. The chemical elements in the outer, cooler layer of the sun absorb certain wavelengths producing these dark lines in the sun's spectrum. Different stars, with different chemical elements in their atmospheres have different dark lines in their spectrums. The spectrum of the moon and the other planets in our solar system have similar dark lines to the sun's spectrum, because the light coming from them is the light of the sun reflected off of them.

Honors won by Fraunhofer include membership in the Bavarian Academy of Science and an honorary doctorate from the University of Erlangen. He is considered the founder of the German optical industry. He was knighted in 1824.

He died of tuberculosis on June 7, 1826.


References:

Kennelly, Colan; "Joseph Von Fraunhofer"; at.u.arizona.edu

"Joseph von Fraunhofer" at pioneers in optics (micro.magnet.fsu.edu)

Joseph von Fraunhofer Wikipedia Entry