Spectroscopy is the study of the interaction between matter and electromagnetic radiation. Spectroscopy originated through the study of visible light dispersed according to its wavelength, by a prism; the concept was expanded to include any interaction with radiative energy as a function of its wavelength or frequency, predominantly in the electromagnetic spectrum, though matter waves and acoustic waves can be considered forms of radiative energy. Spectroscopic data are represented by an emission spectrum, a plot of the response of interest as a function of wavelength or frequency. Spectroscopy in the electromagnetic spectrum, is a fundamental exploratory tool in the fields of physics and astronomy, allowing the composition, physical structure and electronic structure of matter to be investigated at atomic scale, molecular scale, macro scale, over astronomical distances. Important applications arise from biomedical spectroscopy in the areas of tissue analysis and medical imaging. Spectroscopy and spectrography are terms used to refer to the measurement of radiation intensity as a function of wavelength and are used to describe experimental spectroscopic methods.
Spectral measurement devices are referred to as spectrometers, spectrophotometers, spectrographs or spectral analyzers. Daily observations of color can be related to spectroscopy. Neon lighting is a direct application of atomic spectroscopy. Neon and other noble gases have characteristic emission frequencies. Neon lamps use collision of electrons with the gas to excite these emissions. Inks and paints include chemical compounds selected for their spectral characteristics in order to generate specific colors and hues. A encountered molecular spectrum is that of nitrogen dioxide. Gaseous nitrogen dioxide has a characteristic red absorption feature, this gives air polluted with nitrogen dioxide a reddish-brown color. Rayleigh scattering is a spectroscopic scattering phenomenon. Spectroscopic studies were central to the development of quantum mechanics and included Max Planck's explanation of blackbody radiation, Albert Einstein's explanation of the photoelectric effect and Niels Bohr's explanation of atomic structure and spectra.
Spectroscopy is used in physical and analytical chemistry because atoms and molecules have unique spectra. As a result, these spectra can be used to detect and quantify information about the atoms and molecules. Spectroscopy is used in astronomy and remote sensing on Earth. Most research telescopes have spectrographs; the measured spectra are used to determine the chemical composition and physical properties of astronomical objects. One of the central concepts in spectroscopy is its corresponding resonant frequency. Resonances were first characterized in mechanical systems such as pendulums. Mechanical systems that vibrate or oscillate will experience large amplitude oscillations when they are driven at their resonant frequency. A plot of amplitude vs. excitation frequency will have a peak centered at the resonance frequency. This plot is one type of spectrum, with the peak referred to as a spectral line, most spectral lines have a similar appearance. In quantum mechanical systems, the analogous resonance is a coupling of two quantum mechanical stationary states of one system, such as an atom, via an oscillatory source of energy such as a photon.
The coupling of the two states is strongest when the energy of the source matches the energy difference between the two states. The energy of a photon is related to its frequency by E = h ν where h is Planck's constant, so a spectrum of the system response vs. photon frequency will peak at the resonant frequency or energy. Particles such as electrons and neutrons have a comparable relationship, the de Broglie relations, between their kinetic energy and their wavelength and frequency and therefore can excite resonant interactions. Spectra of atoms and molecules consist of a series of spectral lines, each one representing a resonance between two different quantum states; the explanation of these series, the spectral patterns associated with them, were one of the experimental enigmas that drove the development and acceptance of quantum mechanics. The hydrogen spectral series in particular was first explained by the Rutherford-Bohr quantum model of the hydrogen atom. In some cases spectral lines are well separated and distinguishable, but spectral lines can overlap and appear to be a single transition if the density of energy states is high enough.
Named series of lines include the principal, sharp and fundamental series. Spectroscopy is a sufficiently broad field that many sub-disciplines exist, each with numerous implementations of specific spectroscopic techniques; the various implementations and techniques can be classified in several ways. The types of spectroscopy are distinguished by the type of radiative energy involved in the interaction. In many applications, the spectrum is determined by measuring changes in the intensity or frequency of this energy; the types of radiative energy studied include: Electromagnetic radiation was the first source of energy used for spectroscopic studies. Techniques that employ electromagnetic radiation are classified by the wavelength region of the spectrum and include microwave, terahe
Lorentz Medal is a distinction awarded every four years by the Royal Netherlands Academy of Arts and Sciences. It was established in 1925 on the occasion of the 50th anniversary of the doctorate of Hendrik Lorentz; the medal is given for important contributions to theoretical physics, though in the past there have been some experimentalists among its recipients. Many of the award winners received a Nobel Prize
Julian Seymour Schwinger was a Nobel Prize winning American theoretical physicist. He is best known for his work on the theory of quantum electrodynamics, in particular for developing a relativistically invariant perturbation theory, for renormalizing QED to one loop order. Schwinger was a physics professor at several universities. Schwinger is recognized as one of the greatest physicists of the twentieth century, responsible for much of modern quantum field theory, including a variational approach, the equations of motion for quantum fields, he developed the first electroweak model, the first example of confinement in 1+1 dimensions. He is responsible for the theory of multiple neutrinos, Schwinger terms, the theory of the spin 3/2 field. Julian Seymour Schwinger was born in New York City, to Jewish parents from Poland and Benjamin Schwinger, a garment manufacturer, who had migrated to America. Both his father and his mother's parents were prosperous clothing manufacturers, although the family business declined after the Wall Street Crash of 1929.
The family followed the Orthodox Jewish tradition. Schwinger attended the Townsend Harris High School and the City College of New York as an undergraduate before transferring to Columbia University, where he received his B. A. in 1936 and his Ph. D. in 1939 at the age of 21. He worked at the University of California and was appointed to a position at Purdue University. After having worked with Oppenheimer, Schwinger's first regular academic appointment was at Purdue University in 1941. While on leave from Purdue, he worked at the Radiation Laboratory at MIT instead of at the Los Alamos National Laboratory during World War II, he provided theoretical support for the development of radar. After the war, Schwinger left Purdue for Harvard University, where he taught from 1945 to 1974. In 1966 he became the Eugene Higgins professor of physics at Harvard. Schwinger developed an affinity for Green's functions from his radar work, he used these methods to formulate quantum field theory in terms of local Green's functions in a relativistically invariant way.
This allowed him to calculate unambiguously the first corrections to the electron magnetic moment in quantum electrodynamics. Earlier non-covariant work had arrived at infinite answers, but the extra symmetry in his methods allowed Schwinger to isolate the correct finite corrections. Schwinger developed renormalization, formulating quantum electrodynamics unambiguously to one-loop order. In the same era, he introduced non-perturbative methods into quantum field theory, by calculating the rate at which electron-positron pairs are created by tunneling in an electric field, a process now known as the "Schwinger effect"; this effect could not be seen in any finite order in perturbation theory. Schwinger's foundational work on quantum field theory constructed the modern framework of field correlation functions and their equations of motion, his approach started with a quantum action and allowed bosons and fermions to be treated for the first time, using a differential form of Grassman integration.
He gave elegant proofs for the spin-statistics theorem and the CPT theorem, noted that the field algebra led to anomalous Schwinger terms in various classical identities, because of short distance singularities. These were foundational results in field theory, instrumental for the proper understanding of anomalies. In other notable early work and Schwinger formulated the abstract Pauli and Fierz theory of the spin 3/2 field in a concrete form, as a vector of Dirac spinors. In order for the spin-3/2 field to interact some form of supersymmetry is required, Schwinger regretted that he had not followed up on this work far enough to discover supersymmetry. Schwinger discovered that neutrinos come in multiple varieties, one for the electron and one for the muon. Nowadays there are known to be three light neutrinos. In the 1960s, Schwinger formulated and analyzed what is now known as the Schwinger model, quantum electrodynamics in one space and one time dimension, the first example of a confining theory.
He was the first to suggest an electroweak gauge theory, an SU gauge group spontaneously broken to electromagnetic U at long distances. This was extended by his student Sheldon Glashow into the accepted pattern of electroweak unification, he attempted to formulate a theory of quantum electrodynamics with point magnetic monopoles, a program which met with limited success because monopoles are interacting when the quantum of charge is small. Having supervised 73 doctoral dissertations, Schwinger is known as one of the most prolific graduate advisors in physics. Four of his students won Nobel prizes: Roy Glauber, Benjamin Roy Mottelson, Sheldon Glashow and Walter Kohn. Schwinger had a mixed relationship with his colleagues, because he always pursued independent research, different from mainstream fashion. In particular, Schwinger developed the source theory, a phenomenological theory for the physics of elementary particles, a predecessor of the modern effective field theory, it treats quantum fields as long-distance phenomena and uses auxiliary'sources' that resemble currents in classical field theories.
The source theory is a mathematically consistent field theory with derived phenomenological results. The criticisms by his Harvard colleagues led Schwinger to leave the faculty in 1972 for UCLA, it is a story told that Steven Weinberg, who inherited Schwinger's paneled office in Lyman Laboratory, there found a pair of old shoes, with the implied message, "think you can fill these?". At UCLA
Percy Williams Bridgman
Percy Williams Bridgman was an American physicist who received the 1946 Nobel Prize in Physics for his work on the physics of high pressures. He wrote extensively on the scientific method and on other aspects of the philosophy of science; the Bridgman effect and the Bridgman–Stockbarger technique are named after him. Known to family and friends as "Peter", Bridgman was born in Cambridge and grew up in nearby Auburndale, Massachusetts. Bridgman's parents were both born in New England, his father, Raymond Landon Bridgman, was "profoundly religious and idealistic" and worked as a newspaper reporter assigned to state politics. His mother, Mary Ann Maria Williams, was described as "more conventional and competitive". Bridgman attended both elementary and high school in Auburndale, where he excelled at competitions in the classroom, on the playground, while playing chess. Described as both shy and proud, his home life consisted of family music, card games, domestic and garden chores; the family was religious.
However, Bridgman became an atheist. Bridgman entered Harvard University in 1900, studied physics through to his Ph. D. From 1910 until his retirement, he taught at Harvard, becoming a full professor in 1919. In 1905, he began investigating the properties of matter under high pressure. A machinery malfunction led him to modify his pressure apparatus; this was a huge improvement over previous machinery, which could achieve pressures of only 3,000 kgf/cm2. This new apparatus led to an abundance of new findings, including a study of the compressibility and thermal conductivity, tensile strength and viscosity of more than 100 different compounds. Bridgman is known for his studies of electrical conduction in metals and properties of crystals, he is the eponym for Bridgman's thermodynamic equations. Bridgman made many improvements to his high-pressure apparatus over the years, unsuccessfully attempted the synthesis of diamond many times, his philosophy of science book The Logic of Modern Physics advocated operationalism and coined the term operational definition.
In 1938 he participated in the International Committee composed to organise the International Congresses for the Unity of Science. He was one of the 11 signatories to the Russell–Einstein Manifesto. Bridgman married Olive Ware, of Hartford, Connecticut, in 1912. Ware's father, Edmund Asa Ware, was the first president of Atlanta University; the couple were married for 50 years, living most of that time in Cambridge. The family had a summer home in Randolph, New Hampshire, where Bridgman was known as a skilled mountain climber. Bridgman was a "penetrating analytical thinker" with a "fertile mechanical imagination" and exceptional manual dexterity, he was a skilled plumber and carpenter, known to shun the assistance of professionals in these matters. He was fond of music and played the piano, took pride in his flower and vegetable gardens. Bridgman committed suicide by gunshot after suffering from metastatic cancer for some time, his suicide note read. This is the last day I will be able to do it myself."
Bridgman's words have been quoted by many in the assisted suicide debate. Bridgman received Doctors, honoris causa from Stevens Institute, Brooklyn Polytechnic, Princeton and Yale, he received the Bingham Medal from the Society of Rheology, the Rumford Prize from the American Academy of Arts and Sciences, the Elliott Cresson Medal from the Franklin Institute, the Gold Medal from Bakhuys Roozeboom Fund from the Royal Netherlands Academy of Arts and Sciences, the Comstock Prize of the National Academy of Sciences. Bridgman was a member of the American Physical Society and was its President in 1942, he was a member of the American Association for the Advancement of Science, the American Academy of Arts and Sciences, the American Philosophical Society, the National Academy of Sciences. He was a Foreign Member of the Royal Honorary Fellow of the Physical Society of London; the Percy W. Bridgman House, in Massachusetts, is a U. S. National Historic Landmark designated in 1975. In 2014, the Commission on New Minerals and Classification of the International Mineralogical Association approved the name bridgmanite for perovskite-structured SiO3, the Earth's most abundant mineral, in honor of his high-pressure research.
—. Dimensional Analysis. New Haven: Yale University Press. OCLC 840631. —. A Condensed Collection of Thermodynamics Formulas. Cambridge, Massachusetts: Harvard University Press. OCLC 594940689. —. The Logic of Modern Physics. New York: Macmillan. OCLC 17522325. Online excerpt. —. The Thermodynamics of Electrical Phenomena in Metals. New York: Macmillan. —. The Nature of Physical Theory. Dover. OCLC 1298653. —. The Intelligent Individual and Society. New York: MacMillan. OCLC 1488461. —. The Nature of Thermodynamics. Cambridge, Massachusetts: Harvard University Press. ISBN 9780844605128. OCLC 4614803. —. The Physics of High Pressure. London: G. Bell. OCLC 8122603. —. Reflections of a Physicist. New York: Philosophical Library. OCLC 583047. —. Studies in large plastic flow and fracture: with special emphasis on the effects of hydrostatic pressure. New York: McGraw-Hill. OCLC 7435297. — (195
Dordrecht, colloquially Dordt in English named Dort, is a city and municipality in the Western Netherlands, located in the province of South Holland. It is the fourth-largest city of the province, with a population of 118,450; the municipality covers the entire Dordrecht Island often called Het Eiland van Dordt, bordered by the rivers Oude Maas, Beneden Merwede, Nieuwe Merwede, Hollands Diep, Dordtsche Kil. Dordrecht is the largest and most important city in the Drechtsteden and is part of the Randstad, the main conurbation in the Netherlands. Dordrecht has a rich history and culture; the name Dordrecht comes from Thuredrecht. The name seems to mean'thoroughfare'. Earlier etymologists had assumed that the'drecht' suffix came from Latin'trajectum', a ford, but this was rejected in 1996; the Drecht is now supposed to have been derived from ` draeg', which means to tow or drag. Inhabitants of Dordrecht are Dordtenaren. Dordrecht is informally called Dordt by its inhabitants. In earlier centuries, Dordrecht was a major trade port, well known to British merchants, was called Dort in English.
The city was formed in the midst of peat swamps. This river was a branch of the river Dubbel, part of the massive Rhine–Meuse–Scheldt delta complex, near the current Bagijnhof. Around 1120 reference to Dordrecht was made by a remark that count Dirk IV of Holland was murdered in 1049 near "Thuredrech". Dordrecht was granted city rights by William I, Count of Holland, in 1220, making it the oldest city in the present province of South Holland. In fact, Geertruidenberg was the first city in the historical county of Holland to receive city rights, but this municipality is part of the province of Noord-Brabant. In the 12th and 13th centuries, Dordrecht developed into an important market city because of its strategic location, it traded in wine and cereals. Dordrecht was made more important when it was given staple right in 1299. In 1253 a Latin school was founded in Dordrecht, it still is the oldest gymnasium in the Netherlands. From 1600 to 1615 Gerhard Johann Vossius was rector at this school. On 18–19 November 1421, the Saint Elisabeth's flood flooded large parts of southern Holland, causing Dordrecht to become an island.
It was said that over 10,000 people died in the flood, but recent research indicates that it was less than 200 people. In 1572, four years into the Dutch Revolt, representatives of all the cities of Holland, with the exception of Amsterdam, as well as the Watergeuzen, represented by William II de la Marck, gathered in Dordrecht to hold the Eerste Vrije Statenvergadering known as the Unie van Dordrecht; this secret meeting, called by the city of Dordrecht, was a rebellious act since only King Philip II or his stadtholder, at that time the Duke of Alva, were allowed to call a meeting of the States of Holland. During the meeting, the organization and financing of the rebellion against the Spanish occupation was discussed, Phillip II was unanimously denounced, William of Orange was chosen as the rightful stadtholder and recognized as the official leader of the revolt. Orange, represented at the meeting by his assistant Philips of Marnix, was promised financial support of his struggle against the Spanish and at his own request, freedom of religion was declared in all of Holland.
The gathering is regarded as the first important step towards the free and independent Dutch Republic. Other important gatherings such as the Union of Brussels and the Union of Utrecht paved the way for official independence of the Dutch Republic, declared in the Act of Abjuration in 1581; the Union of Dordrecht was held in an Augustinian monastery, nowadays called het Hof. The room in which the meeting was held is called de Statenzaal and features a stained glass window in which the coats of arms of the twelve cities that were present at the meeting can be seen. From November 13, 1618 to May 9, 1619, an important Dutch Reformed Church assembly took place in Dordrecht, referred to as the Synod of Dordrecht; the synod attempted, succeeded, to settle the theological differences of opinion between the central tenets of Calvinism, a new school of thought within the Dutch Reformed Church known as Arminianism, named for its spiritual leader Jacobus Arminius. Arminius' followers were commonly known as Remonstrants, after the 1610 Five Articles of Remonstrance which outlined their points of dissent from the church's official doctrine.
They were opposed by the Contra-Remonstrants, or the Gomarists, who were led by Dutch theologian Franciscus Gomarus. During the Twelve Years' Truce, this in essence purely theological conflict between different factions of the church had in practice spilled over into politics, dividing society along ideological lines, threatening the existence of the young republic by bringing it to the brink of civil war; the synod was attended by Gomarist Dutch delegates and by delegates from Reformed churches in Germany and England. Though it was intended that the synod would bring agreement on the doctrine of predestination among all the Reformed churches, in practice this Dutch synod was concerned with problems facing the Dutch Reformed Church; the opening sessions dealt with a new Dutch translation of the Bible, a catechism, the censorsh
Nuclear magnetic resonance
Nuclear magnetic resonance is a physical phenomenon in which nuclei in a strong static magnetic field are perturbed by a weak oscillating magnetic field and respond by producing an electromagnetic signal with a frequency characteristic of the magnetic field at the nucleus. This process occurs near resonance, when the oscillation frequency matches the intrinsic frequency of the nuclei, which depends on the strength of the static magnetic field, the chemical environment, the magnetic properties of the isotope involved. NMR results from specific magnetic properties of certain atomic nuclei. Nuclear magnetic resonance spectroscopy is used to determine the structure of organic molecules in solution and study molecular physics, crystals as well as non-crystalline materials. NMR is routinely used in advanced medical imaging techniques, such as in magnetic resonance imaging. All isotopes that contain an odd number of protons and/or neutrons have an intrinsic nuclear magnetic moment and angular momentum, in other words a nonzero nuclear spin, while all nuclides with numbers of both have a total spin of zero.
The most used nuclei are 1H and 13C, although isotopes of many other elements can be studied by high-field NMR spectroscopy as well. A key feature of NMR is that the resonance frequency of a particular simple substance is directly proportional to the strength of the applied magnetic field, it is this feature, exploited in imaging techniques. Since the resolution of the imaging technique depends on the magnitude of the magnetic field gradient, many efforts are made to develop increased gradient field strength; the principle of NMR involves three sequential steps: The alignment of the magnetic nuclear spins in an applied, constant magnetic field B0. The perturbation of this alignment of the nuclear spins by a weak oscillating magnetic field referred to as a radio-frequency pulse; the oscillation frequency required for significant perturbation is dependent upon the static magnetic field and the nuclei of observation. The detection of the NMR signal during or after the RF pulse, due to the voltage induced in a detection coil by precession of the nuclear spins around B0.
After an RF pulse, precession occurs with the nuclei's intrinsic Larmor frequency and, in itself, does not involve transitions between spin states or energy levels. The two magnetic fields are chosen to be perpendicular to each other as this maximizes the NMR signal strength; the frequencies of the time-signal response by the total magnetization of the nuclear spins are analyzed in NMR spectroscopy and magnetic resonance imaging. Both use applied magnetic fields of great strength produced by large currents in superconducting coils, in order to achieve dispersion of response frequencies and of high homogeneity and stability in order to deliver spectral resolution, the details of which are described by chemical shifts, the Zeeman effect, Knight shifts; the information provided by NMR can be increased using hyperpolarization, and/or using two-dimensional, three-dimensional and higher-dimensional techniques. NMR phenomena are utilized in low-field NMR, NMR spectroscopy and MRI in the Earth's magnetic field, in several types of magnetometers.
Nuclear magnetic resonance was first described and measured in molecular beams by Isidor Rabi in 1938, by extending the Stern–Gerlach experiment, in 1944, Rabi was awarded the Nobel Prize in Physics for this work. In 1946, Felix Bloch and Edward Mills Purcell expanded the technique for use on liquids and solids, for which they shared the Nobel Prize in Physics in 1952. Yevgeny Zavoisky observed nuclear magnetic resonance in 1941, well before Felix Bloch and Edward Mills Purcell, but dismissed the results as not reproducible. Russell H. Varian filed the "Method and means for correlating nuclear properties of atoms and magnetic fields", U. S. Patent 2,561,490 on July 24, 1951. Varian Associates developed the first NMR unit called NMR HR-30 in 1952. Purcell had worked on the development of radar during World War II at the Massachusetts Institute of Technology's Radiation Laboratory, his work during that project on the production and detection of radio frequency power and on the absorption of such RF power by matter laid the foundation for his discovery of NMR in bulk matter.
Rabi and Purcell observed that magnetic nuclei, like 1H and 31P, could absorb RF energy when placed in a magnetic field and when the RF was of a frequency specific to the identity of the nuclei. When this absorption occurs, the nucleus is described as being in resonance. Different atomic nuclei within a molecule resonate at different frequencies for the same magnetic field strength; the observation of such magnetic resonance frequencies of the nuclei present in a molecule allows any trained user to discover essential chemical and structural information about the molecule. The development of NMR as a technique in analytical chemistry and biochemistry parallels the development of electromagnetic technology and advanced electronics and their introduction into civilian use. All nucleons, neutrons and protons, composing any atomic nucleus, have the intrinsic quantum property of spin, an intrinsic angular momentum analogous to the classical angular momentum of a spinning sphere; the overall spin of the nucleus is determined b
Edward Mills Purcell
Edward Mills Purcell was an American physicist who shared the 1952 Nobel Prize for Physics for his independent discovery of nuclear magnetic resonance in liquids and in solids. Nuclear magnetic resonance has become used to study the molecular structure of pure materials and the composition of mixtures. Born and raised in Taylorville, Purcell received his BSEE in electrical engineering from Purdue University, followed by his M. A. and Ph. D. in physics from Harvard University. He was a member of the Alpha Xi chapter of the Phi Kappa Sigma Fraternity while at Purdue. After spending the years of World War II working at the MIT Radiation Laboratory on the development of microwave radar, Purcell returned to Harvard to do research. In December 1946, he discovered nuclear magnetic resonance with his colleagues Robert Pound and Henry Torrey. NMR provides scientists with an elegant and precise way of determining chemical structure and properties of materials, is used in physics and chemistry, it is the basis of magnetic resonance imaging, one of the most important medical advances of the 20th century.
For his discovery of NMR, Purcell shared the 1952 Nobel Prize in physics with Felix Bloch of Stanford University. Purcell made contributions to astronomy as the first to detect radio emissions from neutral galactic hydrogen, affording the first views of the spiral arms of the Milky Way; this observation helped launch the field of radio astronomy, measurements of the 21 cm line are still an important technique in modern astronomy. He has made seminal contributions to solid state physics, with studies of spin-echo relaxation, nuclear magnetic relaxation, negative spin temperature. With Norman F. Ramsey, he was the first to question the CP symmetry of particle physics. Purcell was the recipient of many awards for his scientific and civic work, he served as science advisor to Presidents Dwight D. Eisenhower, John F. Kennedy, Lyndon B. Johnson, he was president of the American Physical Society, a member of the American Philosophical Society, the National Academy of Sciences, the American Academy of Arts and Sciences.
He was awarded the National Medal of Science in 1979, the Jansky Lectureship before the National Radio Astronomy Observatory. Purcell was inducted into his Fraternity's Hall of Fame as the first Phi Kap to receive a Nobel Prize. Purcell was the author of Magnetism; the book, a Sputnik-era project funded by an NSF grant, was influential for its use of relativity in the presentation of the subject at this level. The 1965 edition, now available due to a condition of the federal grant, was published as a volume of the Berkeley Physics Course. Half a century the book is in print as a commercial third edition, as Purcell and Morin. Purcell is remembered by biologists for his famous lecture "Life at Low Reynolds Number", in which he explained a principle referred to as the Scallop theorem. Purcell effect Relativistic electromagnetism Magnetic resonance imaging 1979 Audio Interview with Edward Purcell by Martin Sherwin Voices of the Manhattan Project Biography and Bibliographic Resources, from the Office of Scientific and Technical Information, United States Department of Energy National Academy of Sciences biography Edward Mills Purcell The story of the 21 cm line experiment, including a photo of Purcell Oral History Transcript — Dr. Edward Purcell, June 8, 1977 Edward Mills Purcell at the Mathematics Genealogy Project