Niels Henrik David Bohr was a Danish physicist who made foundational contributions to understanding atomic structure and quantum theory, for which he received the Nobel Prize in Physics in 1922. Bohr was a philosopher and a promoter of scientific research. Bohr developed the Bohr model of the atom, in which he proposed that energy levels of electrons are discrete and that the electrons revolve in stable orbits around the atomic nucleus but can jump from one energy level to another. Although the Bohr model has been supplanted by other models, its underlying principles remain valid, he conceived the principle of complementarity: that items could be separately analysed in terms of contradictory properties, like behaving as a wave or a stream of particles. The notion of complementarity dominated Bohr's thinking in both philosophy. Bohr founded the Institute of Theoretical Physics at the University of Copenhagen, now known as the Niels Bohr Institute, which opened in 1920. Bohr mentored and collaborated with physicists including Hans Kramers, Oskar Klein, George de Hevesy, Werner Heisenberg.
He predicted the existence of a new zirconium-like element, named hafnium, after the Latin name for Copenhagen, where it was discovered. The element bohrium was named after him. During the 1930s, Bohr helped refugees from Nazism. After Denmark was occupied by the Germans, he had a famous meeting with Heisenberg, who had become the head of the German nuclear weapon project. In September 1943, word reached Bohr that he was about to be arrested by the Germans, he fled to Sweden. From there, he was flown to Britain, where he joined the British Tube Alloys nuclear weapons project, was part of the British mission to the Manhattan Project. After the war, Bohr called for international cooperation on nuclear energy, he was involved with the establishment of CERN and the Research Establishment Risø of the Danish Atomic Energy Commission and became the first chairman of the Nordic Institute for Theoretical Physics in 1957. Bohr was born in Copenhagen, Denmark, on 7 October 1885, the second of three children of Christian Bohr, a professor of physiology at the University of Copenhagen, Ellen Adler Bohr, who came from a wealthy Danish Jewish family prominent in banking and parliamentary circles.
He had an elder sister, a younger brother Harald. Jenny became a teacher, while Harald became a mathematician and Olympic footballer who played for the Danish national team at the 1908 Summer Olympics in London. Bohr was a passionate footballer as well, the two brothers played several matches for the Copenhagen-based Akademisk Boldklub, with Bohr as goalkeeper. Bohr was educated at Gammelholm Latin School. In 1903, Bohr enrolled as an undergraduate at Copenhagen University, his major was physics, which he studied under Professor Christian Christiansen, the university's only professor of physics at that time. He studied astronomy and mathematics under Professor Thorvald Thiele, philosophy under Professor Harald Høffding, a friend of his father. In 1905, a gold medal competition was sponsored by the Royal Danish Academy of Sciences and Letters to investigate a method for measuring the surface tension of liquids, proposed by Lord Rayleigh in 1879; this involved measuring the frequency of oscillation of the radius of a water jet.
Bohr conducted a series of experiments using his father's laboratory in the university. To complete his experiments, he had to make his own glassware, creating test tubes with the required elliptical cross-sections, he went beyond the original task, incorporating improvements into both Rayleigh's theory and his method, by taking into account the viscosity of the water, by working with finite amplitudes instead of just infinitesimal ones. His essay, which he submitted at the last minute, won the prize, he submitted an improved version of the paper to the Royal Society in London for publication in the Philosophical Transactions of the Royal Society. Harald became the first of the two Bohr brothers to earn a master's degree, which he earned for mathematics in April 1909. Niels took another nine months to earn his. Students had to submit a thesis on a subject assigned by their supervisor. Bohr's supervisor was Christiansen, the topic he chose was the electron theory of metals. Bohr subsequently elaborated his master's thesis into his much-larger Doctor of Philosophy thesis.
He surveyed the literature on the subject, settling on a model postulated by Paul Drude and elaborated by Hendrik Lorentz, in which the electrons in a metal are considered to behave like a gas. Bohr extended Lorentz's model, but was still unable to account for phenomena like the Hall effect, concluded that electron theory could not explain the magnetic properties of metals; the thesis was accepted in April 1911, Bohr conducted his formal defence on 13 May. Harald had received his doctorate the previous year. Bohr's thesis was groundbreaking, but attracted little interest outside Scandinavia because it was written in Danish, a Copenhagen University requirement at the time. In 1921, the Dutch physicist Hendrika Johanna van Leeuwen would independently derive a theorem from Bohr's thesis, today known as the Bohr–van Leeuwen theorem. In 1910, Bohr met the sister of the mathematician Niels Erik Nørlund. Bohr resigned his membership in the Church of Denmark on 16 April 1912, he and Margrethe were married in a civil ceremony at the town hall in Slagelse on 1 August.
Years his brother Harald left the church before getting married. Bohr and Margrethe had six sons; the oldest, died in a boating acciden
Tübingen is a traditional university town in central Baden-Württemberg, Germany. It is situated 30 km south of the state capital, Stuttgart, on a ridge between the Neckar and Ammer rivers; as of 2014 about one in three people living in Tübingen is a student. North of the city lies the Schönbuch, a densely wooded nature park; the Swabian Alb mountains rise about 13 km to the southeast of Tübingen. The Ammer and Steinlach rivers discharge into the Neckar river, which flows right through the town, just south of the medieval old town in an easterly direction. Large parts of the city are hilly, with the Schlossberg and the Österberg in the city centre and the Schnarrenberg and Herrlesberg, among others, rising adjacent to the inner city; the highest point is at about 500 m above sea level near Bebenhausen in the Schönbuch forest, while the lowest point is 305 m in the town's eastern Neckar valley. Nearby the Botanical Gardens of the city's university, in a small forest called Elysium, lies the geographical centre of the state of Baden-Württemberg.
Tübingen is the capital of an eponymous district and an eponymous administrative region, before 1973 called Südwürttemberg-Hohenzollern. Tübingen is, with nearby Reutlingen, one of the two centre cities of the Neckar-Alb region. Administratively, it is not part of the Stuttgart Region, bordering it to the west. However, the city and northern parts of its district can be regarded as belonging to that region in a wider regional and cultural context; the area was first settled in the 12th millennium BC. The Romans left some traces here in AD 85. Tübingen itself dates from the 7th century, when the region was populated by the Alamanni; some argue that the Battle of Solicinium was fought at Spitzberg, a mountain in Tübingen, in AD 367, although there is no evidence for this. Tübingen first appears in official records in 1191, the local castle, Hohentübingen, has records going back to 1078 when it was besieged by Henry IV, king of Germany, its name transcribed in Medieval Latin as Tuingia and Twingia.
From 1146, Count Hugo V was promoted to count palatine, as Hugo I, establishing Tübingen as the capital of a County Palatine of Tübingen. By 1231, Tübingen was a civitas indicating recognition of a court system. In 1262, an Augustinian monastery was established by Pope Alexander IV in Tübingen, in 1272, a Franciscan monastery followed; the latter existed until Duke Ulrich of Würtemmberg disestablished it in 1535 in course of the Protestant Reformation, which the Duchy of Württemberg followed. In 1300, a Latin school was founded. In 1342, the county palatine was sold to Ulrich III, Count of Württemberg and incorporated into the County of Württemberg. Between 1470 and 1483, St. George's Collegiate Church was built; the collegiate church offices provided the opportunity for what soon afterwards became the most significant event in Tübingen's history: the founding of the Eberhard Karls University by Duke Eberhard im Bart of Württemberg in 1477, thus making it one of the oldest universities in Central Europe.
It became soon renowned as one of the most influential places of learning in the Holy Roman Empire for theology. Today, the university is still the biggest source of income for the residents of the city and one of the biggest universities in Germany with more than 22,000 students. Between 1622 and 1625, the Catholic League occupied Lutheran Württemberg in the course of the Thirty Years' War. In the summer of 1631, the city was raided. In 1635/36 the city was hit by the Plague. In 1638, Swedish troops conquered Tübingen. Towards the end of the war, French troops occupied the city from 1647 until 1649. In 1789, parts of the old town burned down, but were rebuilt in the original style. In 1798 the Allgemeine Zeitung, a leading newspaper in early 19th-century Germany, was founded in Tübingen by Johann Friedrich Cotta. From 1807 until 1843, the poet Friedrich Hölderlin lived in Tübingen in a tower overlooking the Neckar. In the Nazi era, the Tübingen Synagogue was burned in the Kristallnacht on November 9, 1938.
The Second World War left the city unscathed because of the peace initiative of a local doctor, Theodor Dobler. It became part of the French occupational zone. From 1946 to 1952, Tübingen was the capital of the newly formed state of Württemberg-Hohenzollern, before the state of Baden-Württemberg was created by merging Baden, Württemberg-Baden and Württemberg-Hohenzollern; the French troops had a garrison stationed in the south of the city until the end of the Cold War in the 1990s. In the 1960s, Tübingen was one of the centres of the German student movement and the Protests of 1968 and has since shaped left and green political views; some radicalized Tübingen students supported the leftist Rote Armee Fraktion terrorist group, with active member Gudrun Ensslin, a local and a Tübingen student from 1960 to 1963, joining the group in 1968. Although noticing such things today is impossible, as as the 1950s, Tübingen was a socioeconomically divided city, with poor local farmers and tradesmen living along the Stadtgraben and students and academics residing around the Alte Aula and the Burse, the old university buildings.
There, hanging on the Cottahaus, a sign commemorates Goethe's stay of a few weeks while visiting his publisher. The Ge
Thermal expansion is the tendency of matter to change its shape and volume in response to a change in temperature. Temperature is a monotonic function of the average molecular kinetic energy of a substance; when a substance is heated, the kinetic energy of its molecules increases. Thus, the molecules begin vibrating/moving more and maintain a greater average separation. Materials which contract with increasing temperature are unusual; the relative expansion divided by the change in temperature is called the material's coefficient of thermal expansion and varies with temperature. If an equation of state is available, it can be used to predict the values of the thermal expansion at all the required temperatures and pressures, along with many other state functions. A number of materials contract on heating within certain temperature ranges. For example, the coefficient of thermal expansion of water drops to zero as it is cooled to 3.983 °C and becomes negative below this temperature. Pure silicon has a negative coefficient of thermal expansion for temperatures between about 18 and 120 kelvins.
Unlike gases or liquids, solid materials tend to keep their shape. Thermal expansion decreases with increasing bond energy, which has an effect on the melting point of solids, so, high melting point materials are more to have lower thermal expansion. In general, liquids expand more than solids; the thermal expansion of glasses is higher compared to that of crystals. At the glass transition temperature, rearrangements that occur in an amorphous material lead to characteristic discontinuities of coefficient of thermal expansion and specific heat; these discontinuities allow detection of the glass transition temperature where a supercooled liquid transforms to a glass. Absorption or desorption of water can change the size of many common materials. Common plastics exposed to water can, in the long term, expand by many percent; the coefficient of thermal expansion describes how the size of an object changes with a change in temperature. It measures the fractional change in size per degree change in temperature at a constant pressure.
Several types of coefficients have been developed: volumetric and linear. The choice of coefficient depends on the particular application and which dimensions are considered important. For solids, one might only be concerned over some area; the volumetric thermal expansion coefficient is the most basic thermal expansion coefficient, the most relevant for fluids. In general, substances expand or contract when their temperature changes, with expansion or contraction occurring in all directions. Substances that expand at the same rate in every direction are called isotropic. For isotropic materials, the area and volumetric thermal expansion coefficient are approximately twice and three times larger than the linear thermal expansion coefficient. Mathematical definitions of these coefficients are defined below for solids and gases. In the general case of a gas, liquid, or solid, the volumetric coefficient of thermal expansion is given by α V = 1 V p The subscript p indicates that the pressure is held constant during the expansion, the subscript V stresses that it is the volumetric expansion that enters this general definition.
In the case of a gas, the fact that the pressure is held constant is important, because the volume of a gas will vary appreciably with pressure as well as temperature. For a gas of low density this can be seen from the ideal gas law; when calculating thermal expansion it is necessary to consider whether the body is free to expand or is constrained. If the body is free to expand, the expansion or strain resulting from an increase in temperature can be calculated by using the applicable coefficient of Thermal Expansion. If the body is constrained so that it cannot expand internal stress will be caused by a change in temperature; this stress can be calculated by considering the strain that would occur if the body were free to expand and the stress required to reduce that strain to zero, through the stress/strain relationship characterised by the elastic or Young's modulus. In the special case of solid materials, external ambient pressure does not appreciably affect the size of an object and so it is not necessary to consider the effect of pressure changes.
Common engineering solids have coefficients of thermal expansion that do not vary over the range of temperatures where they are designed to be used, so where high accuracy is not required, practical calculations can be based on a constant, value of the coefficient of expansion. Linear expansion means change in one dimension as opposed to change in volume. To a first approximation, the change in length measurements of an object due to thermal expansion is related to temperature change by a "Coefficient of linear th
University of Tübingen
The University of Tübingen the Eberhard Karls University of Tübingen, is a public research university located in the city of Tübingen, Baden-Württemberg, Germany. It is a German Excellence University, Tübingen is ranked as one of the best universities in Germany and is known as a centre for the study of medicine and theology and religion; the university's noted alumni include numerous presidents, ministers, EU Commissioners and judges of the Federal Constitutional Court. The university is associated with eleven Nobel laureates in the fields of medicine and chemistry; the University of Tübingen was founded in 1477 by Count Eberhard V the first Duke of Württemberg, a civic and ecclesiastic reformer who established the school after becoming absorbed in the Renaissance revival of learning during his travels to Italy. Its first rector was Johannes Nauclerus, its present name was conferred on it in 1769 by Duke Karl Eugen who appended his first name to that of the founder. The university became the principal university of the kingdom of Württemberg.
Today, it is one of nine state universities funded by the German federal state of Baden-Württemberg. The University of Tübingen has a history of innovative thought in theology, in which the university and the Tübinger Stift are famous to this day. Philipp Melanchthon, the prime mover in building the German school system and a chief figure in the Protestant Reformation, helped establish its direction. Among Tübingen's eminent students have been the astronomer Johannes Kepler. "The Tübingen Three" refers to Hölderlin and Schelling, who were roommates at the Tübinger Stift. Theologian Helmut Thielicke revived postwar Tübingen when he took over a professorship at the reopened theological faculty in 1947, being made administrative head of the university and President of the Chancellor's Conference in 1951; the university rose to the height of its prominence in the middle of the 19th century with the teachings of poet and civic leader Ludwig Uhland and the Protestant theologian Ferdinand Christian Baur, whose circle and students became known as the "Tübingen School", which pioneered the historical-critical analysis of biblical and early Christian texts, an approach referred to as "higher criticism."
The University of Tübingen was the first German university to establish a faculty of natural sciences, in 1863. DNA was discovered in 1868 at the University of Tübingen by Friedrich Miescher. Christiane Nüsslein-Volhard, the first female Nobel Prize winner in medicine in Germany works at Tübingen; the faculty for economics and business was founded in 1817 as the "Staatswissenschaftliche Fakultät" and was the first of its kind in Germany. The University played a leading role in efforts to legitimize the policies of the Third Reich as "scientific". Before the victory of the Nazi Party in the general election in March 1933, there were hardly any Jewish faculty and a few Jewish students. Physicist Hans Bethe was dismissed on 20 April 1933 because of "non-Aryan" origin. Religion professor Traugott Konstantin Oesterreich and the mathematician Erich Kamke were forced to take early retirement in both cases the "non-Aryan" origin of their wives. At least 1158 people were sterilized at the University Hospital.
In 1966, Joseph Ratzinger, who would become Pope Benedict XVI, was appointed to a chair in dogmatic theology in the Faculty of Catholic Theology at Tübingen, where he was a colleague of Hans Küng. In 1967, Jürgen Moltmann, one of the most influential Protestant theologians of the 20th century, was appointed Professor of Systematic Theology in the Faculty of Protestant Theology. Drafted in 1944 by Nazi Germany, he was an Allied prisoner of war 1945-1948, he was influenced by friend Ernst Bloch, the Marxist philosopher. In 1970, the university was restructured into a series of faculties as independent departments of study and research after the manner of French universities; the university made the headlines in November 2009 when a group of left-leaning students occupied one of the main lecture halls, the Kupferbau, for several days. The students' goal was to protest tuition fees and maintain that education should be free for everyone. In May 2010, Tübingen joined the Matariki Network of Universities together with Dartmouth College, Durham University, Queen’s University, University of Otago, University of Western Australia and Uppsala University.
The University of Tübingen undertakes a broad range of research projects in various fields. Among the more prominent ones in the natural sciences are the Hertie Institute for Clinical Brain Research, which focuses on general and cellular neurology as well as neurodegeneration, the Centre for Interdisciplinary Clinical Research, which deals with cell biology in diagnostics and therapy of organ system diseases. In the liberal arts, the University of Tübingen is noteworthy for having the only faculty of rhetoric in Germany – the department was founded by Walter Jens, an important intellectual and literary critic; the university boasts continued pre-eminence in its centuries-old traditions of research in the fields of philosophy and philology. Since at least the nineteenth century, Tübingen has been the home of world-class research in prehistoric studies and the study of antiquity, including the study of the ancient Near East.
Samuel Abraham Goudsmit was a Dutch-American physicist famous for jointly proposing the concept of electron spin with George Eugene Uhlenbeck in 1925. Goudsmit was born in Netherlands, of Dutch Jewish descent, he was the son of Isaac Goudsmit, a manufacturer of water-closets, Marianne Goudsmit-Gompers, who ran a millinery shop. In 1943 his parents were deported to a concentration camp by the German occupiers of the Netherlands and were murdered there. Goudsmit studied physics at the University of Leiden under Paul Ehrenfest, where he obtained his PhD in 1927. After receiving his PhD, Goudsmit served as a Professor at the University of Michigan between 1927 and 1946. In 1930 he co-authored a text with Linus Pauling titled The Structure of Line Spectra. During World War II he worked at the Massachusetts Institute of Technology, he was the scientific head of the Alsos Mission and reached the German group of nuclear physicists around Werner Heisenberg and Otto Hahn at Hechingen in advance of the French physicist Yves Rocard, who had succeeded in recruiting German scientists to come to France.
Alsos, part of the Manhattan Project, was designed to assess the progress of the Nazi atomic bomb project. In the book Alsos, published in 1947, Goudsmit concludes that the Germans did not get close to creating a weapon, he attributed this to the inability of science to function under a totalitarian state and the German scientists' lack of understanding how to make an atomic bomb. Both of these conclusions have been disputed by historians and contradicted by the fact that the totalitarian Soviet state produced the bomb shortly after the book's release. After the war he was a professor at Northwestern University, from 1948-1970 was a senior scientist at the Brookhaven National Laboratory, chairing the Physics Department 1952-1960, he meanwhile became well known as the Editor-in-chief of the leading physics journal Physical Review, published by the American Physical Society. In July 1958 he started the journal Physical Review Letters. On his retirement as editor in 1974, Goudsmit moved to the faculty of the University of Nevada in Reno, where he remained until his death four years later.
He made some scholarly contributions to Egyptology published in Expedition, Summer 1972, pp. 13–16. The Samuel A. Goudsmit Collection of Egyptian Antiquities resides at the Kelsey Museum of Archaeology at the University of Michigan in Ann Arbor, Michigan. Goudsmit became a corresponding member of the Royal Netherlands Academy of Arts and Sciences in 1939, though he resigned the next year, he was readmitted in 1950. Goudsmit, Samuel A.. Alsos. EBook published by Plunkett Lake Press in 2017. ASIN B075WCCQBN Goudsmit, Samuel A.. Time. Time-Life Science Library. Goudsmit, S.. "Multiple Scattering of Electrons". Phys. Rev. 57: 24. Bibcode:1940PhRv...57...24G. Doi:10.1103/physrev.57.24. Annotated Bibliography for Samuel Abraham Goudsmit from the Alsos Digital Library for Nuclear Issues Goudsmit on the discovery of electron spin A collection of digitized materials related to Goudsmit's and Linus Pauling's structural chemistry research. National Academy of Sciences Biographical Memoir
Robert Andrews Millikan
Robert Andrews Millikan was an American experimental physicist honored with the Nobel Prize for Physics in 1923 for the measurement of the elementary electric charge and for his work on the photoelectric effect. Millikan graduated from Oberlin College in 1891 and obtained his doctorate at Columbia University in 1895. In 1896 he became an assistant at the University of Chicago, where he became a full professor in 1910. In 1909 Millikan began a series of experiments to determine the electric charge carried by a single electron, he began by measuring the course of charged water droplets in an electric field. The results suggested that the charge on the droplets is a multiple of the elementary electric charge, but the experiment was not accurate enough to be convincing, he obtained more precise results in 1910 with his famous oil-drop experiment in which he replaced water with oil. In 1914 Millikan took up with similar skill the experimental verification of the equation introduced by Albert Einstein in 1905 to describe the photoelectric effect.
He used this same research to obtain an accurate value of Planck’s constant. In 1921 Millikan left the University of Chicago to become director of the Norman Bridge Laboratory of Physics at the California Institute of Technology in Pasadena, California. There he undertook a major study of the radiation that the physicist Victor Hess had detected coming from outer space. Millikan proved that this radiation is indeed of extraterrestrial origin, he named it "cosmic rays." As chairman of the Executive Council of Caltech from 1921 until his retirement in 1945, Millikan helped to turn the school into one of the leading research institutions in the United States. He served on the board of trustees for Science Service, now known as Society for Science & the Public, from 1921 to 1953. Robert Andrews Millikan was born on March 1868, in Morrison, Illinois. Millikan went to high school in Iowa. Millikan received a bachelor's degree in the classics from Oberlin College in 1891 and his doctorate in physics from Columbia University in 1895 – he was the first to earn a Ph.
D. from that department. At the close of my sophomore year my Greek professor asked me to teach the course in elementary physics in the preparatory department during the next year. To my reply that I did not know any physics at all, his answer was, "Anyone who can do well in my Greek can teach physics." "All right," said I, "you will have to take the consequences, but I will try and see what I can do with it." I at once purchased an Avery's Elements of Physics, spent the greater part of my summer vacation of 1889 at home – trying to master the subject. I doubt if I have taught better in my life than in my first course in physics in 1889. I was so intensely interested in keeping my knowledge ahead of that of the class that they may have caught some of my own interest and enthusiasm. Millikan's enthusiasm for education continued throughout his career, he was the coauthor of a popular and influential series of introductory textbooks, which were ahead of their time in many ways. Compared to other books of the time, they treated the subject more in the way in which it was thought about by physicists.
They included many homework problems that asked conceptual questions, rather than requiring the student to plug numbers into a formula. Starting in 1908, while a professor at the University of Chicago, Millikan worked on an oil-drop experiment in which he measured the charge on a single electron. J. J. Thomson had discovered the charge-to-mass ratio of the electron. However, the actual charge and mass values were unknown. Therefore, if one of these two values were to be discovered, the other could be calculated. Millikan and his graduate student Harvey Fletcher used the oil-drop experiment to measure the charge of the electron. Professor Millikan took sole credit, in return for Harvey Fletcher claiming full authorship on a related result for his dissertation. Millikan went on to win the 1923 Nobel Prize for Physics, in part for this work, Fletcher kept the agreement a secret until his death. After a publication on his first results in 1910, contradictory observations by Felix Ehrenhaft started a controversy between the two physicists.
After improving his setup, Millikan published his seminal study in 1913. The elementary charge is one of the fundamental physical constants, accurate knowledge of its value is of great importance, his experiment measured the force on tiny charged droplets of oil suspended against gravity between two metal electrodes. Knowing the electric field, the charge on the droplet could be determined. Repeating the experiment for many droplets, Millikan showed that the results could be explained as integer multiples of a common value, the charge of a single electron; that this is somewhat lower than the modern value of 1.602 176 53 x 10−19 coulomb is due to Millikan's use of an inaccurate value for the viscosity of air. Although at the time of Millikan's oil-drop experiments it was becoming clear that there exist such things as subatomic particles, not everyone was convinced. Experimenting with cathode rays in 1897, J. J. Thomson had discovered negatively charged'corpuscles', as he called them, with a charge-to-mass ratio 1840 times that of a hydrogen ion.
Similar results had been found by Walter Kaufmann. Most of what was known about electricity and magnetism, could be explained on the basis that charge is a continuous variable.
Henry Augustus Rowland
Prof Henry Augustus Rowland FRS HFRSE was an American physicist. Between 1899 and 1901 he served as the first president of the American Physical Society, he is remembered today for the high quality of the diffraction gratings he made and for the work he did with them on the solar spectrum. Rowland was born in Honesdale, where his father Henry Augustus Rowland was the Presbyterian pastor of a local church. From an early age he exhibited marked scientific tastes and spent all his spare time in electrical and chemical experiments. At the Rensselaer Polytechnic Institute at Troy, N. Y. he graduated in 1870, he obtained an engagement on the Western New York railway. But the work there was not to his liking, after a short time he gave it up for an instructorship in natural science at the University of Wooster, which in turn he resigned in order to return to Troy as assistant professor of physics. In 1876, he became the first occupant of the chair of physics at the Johns Hopkins University, Baltimore, a position which he retained until his premature death on April 16, 1901.
Rowland was one of the most brilliant American scientists of his day, it is curious that at first his merits were not perceived in his own country. He was unable to secure the publication of many of his early scientific papers; when the managers of the Johns Hopkins University asked advice in Europe as to whom they should make their professor of physics, he was pointed out in all quarters as the best man for the post. In the interval between his election and the assumption of his duties at Baltimore, he studied physics under Hermann von Helmholtz in his laboratory in Berlin, carried out a well-known research on the effect of an electrically charged body in motion, showing it to give rise to a magnetic field; as soon as he was settled at Baltimore, two important pieces of work engaged his attention. One was a redetermination of the ohm. For this he obtained a value, different from that ascertained by the committee of the British Association appointed for the purpose, but he had the satisfaction of seeing his own result accepted as the more correct of the two.
The other was a new determination of the mechanical equivalent of heat. In this he used J. P. Joule's paddle-wheel method, though with many improvements, the whole apparatus being on a larger scale and the experiments being conducted over a wider range of temperature, he obtained a result distinctly higher than Joule's final figure. In 1882, before the Physical Society of London, he gave a description of the diffraction gratings, with which his name is specially associated, which have been of enormous advantage to astronomical spectroscopy; these gratings consist of pieces of metal or glass ruled by means of a diamond point with a large number of parallel lines, on the extreme accuracy of which their efficiency depends. For their production, dividing engines of extraordinary trueness and delicacy were required, in the construction of such machines Rowland's engineering skill brought him conspicuous success; the results of his labors may be found in the elaborate Photographic Map of the Normal Solar Spectrum and the Table of Solar Wave-Lengths.
In the years of his life he was engaged in developing a system of multiplex telegraphy. He authored A Plea for Pure Science, in 1883 an important document for the understanding of the relationship between science in university and in commercial contexts in the late nineteenth and early twentieth century; the National Academy of Sciences awarded Rowland the Henry Draper Medal in 1890 for his contributions to astrophysics. He won the Matteucci Medal in 1895; the Henry August Rowland House in Baltimore was designated a U. S. National Historic Landmark; this article incorporates text from a publication now in the public domain: Chisholm, Hugh, ed.. "Rowland, Henry Augustus". Encyclopædia Britannica. Cambridge University Press. Works written by or about Henry Augustus Rowland at Wikisource American Institute of Physics page on Rowland's work and published papers Astrophysical Journal, 1901, vol. 13, p.241 Monthly Notices of the Royal Astronomical Society, 1902 p.245 The Physical Papers of Henry Augustus Rowland Henry Augustus Rowland — Biographical Memoirs of the National Academy of Sciences