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N<\/span>iels Henrik David Bohr\u00a0was born in Copenhagen on October 7, 1885, as the son of Christian Bohr, Professor of Physiology at Copenhagen University, and his wife Ellen,\u00a0n\u00e9e<\/i>\u00a0Adler. Niels, together with his younger brother Harald (the future Professor in Mathematics), grew up in an atmosphere most favourable to the development of his genius \u2013 his father was an eminent physiologist and was largely responsible for awakening his interest in physics while still at school, his mother came from a family distinguished in the field of education.<\/p>\nAfter matriculation at the Gammelholm Grammar School in 1903, he entered Copenhagen University where he came under the guidance of Professor C. Christiansen, a profoundly original and highly endowed physicist, and took his Master\u2019s degree in Physics in 1909 and his Doctor\u2019s degree in 1911.<\/p>\n
While still a student, the announcement by the Academy of Sciences in Copenhagen of a prize to be awarded for the solution of a certain scientific problem, caused him to take up an experimental and theoretical investigation of the surface tension by means of oscillating fluid jets. This work, which he carried out in his father\u2019s laboratory and for which he received the prize offered (a gold medal), was published in the Transactions of the Royal Society, 1908.<\/p>\n
Bohr\u2019s subsequent studies, however, became more and more theoretical in character, his doctor\u2019s disputation being a purely theoretical piece of work on the explanation of the properties of the metals with the aid of the electron theory, which remains to this day a classic on the subject. It was in this work that Bohr was first confronted with the implications of Planck\u2019s quantum theory of radiation.<\/p>\n
In the autumn of 1911 he made a stay at Cambridge, where he profited by following the experimental work going on in the Cavendish Laboratory under\u00a0Sir J.J. Thomson\u2019s\u00a0guidance, at the same time as he pursued own theoretical studies. In the spring of 1912 he was at work inProfessor Rutherford\u2019s\u00a0laboratory in Manchester, where just in those years such an intensive scientific life and activity prevailed as a consequence of that investigator\u2019s fundamental inquiries into the radioactive phenomena. Having there carried out a theoretical piece of work on the absorption of alpha rays which was published in the\u00a0Philosophical Magazine<\/i>, 1913, he passed on to a study of the structure of atoms on the basis of Rutherford\u2019s discovery of the atomic nucleus. By introducing conceptions borrowed from the Quantum Theory as established by Planck, which had gradually come to occupy a prominent position in the science of theoretical physics, he succeeded in working out and presenting a picture of atomic structure that, with later improvements (mainly as a result of Heisenberg\u2019s ideas in 1925), still fitly serves as an elucidation of the physical and chemical properties of the elements.<\/p>\n
In 1913-1914 Bohr held a Lectureship in Physics at Copenhagen University and in 1914-1916 a similar appointment at the Victoria University in Manchester. In 1916 he was appointed Professor of Theoretical Physics at Copenhagen University, and since 1920 (until his death in 1962) he was at the head of the Institute for Theoretical Physics, established for him at that university.<\/p>\n
Recognition of his work on the structure of atoms came with the award of the Nobel Prize for 1922.<\/p>\n
Bohr\u2019s activities in his Institute were since 1930 more and more directed to research on the constitution of the atomic nuclei, and of their transmutations and disintegrations. In 1936 he pointed out that in nuclear processes the smallness of the region in which interactions take place, as well as the strength of these interactions, justify the transition processes to be described more in a classical way than in the case of atoms (Cf. \u00a0\u00bbNeutron capture and nuclear constitution\u00ab,\u00a0Nature<\/i>, 137 (1936) 344).<\/p>\n
A liquid drop would, according to this view, give a very good picture of the nucleus. This so-called\u00a0liquid droplet theory<\/i>\u00a0permitted the understanding of the mechanism of nuclear fission, when the splitting of uranium was discovered by Hahn and Strassmann, in 1939, and formed the basis of important theoretical studies in this field (among others, by Frisch and Meitner).<\/p>\n
Bohr also contributed to the clarification of the problems encountered in quantum physics, in particular by developing the\u00a0concept of complementarity<\/i>. Hereby he could show how deeply the changes in the field of physics have affected fundamental features of our scientific outlook and how the consequences of this change of attitude reach far beyond the scope of atomic physics and touch upon all domains of human knowledge. These views are discussed in a number of essays, written during the years 1933-1962. They are available in English, collected in two volumes with the title Atomic Physics and Human Knowledge and Essays 1958-1962 on\u00a0Atomic Physics and Human Knowledge<\/i>, edited by John Wiley and Sons, New York and London, in 1958 and 1963, respectively.<\/p>\n
Among Professor Bohr\u2019s numerous writings (some 115 publications), three appearing as books in the English language may be mentioned here as embodying his principal thoughts:\u00a0The Theory of Spectra and Atomic Constitution<\/i>, University Press, Cambridge, 1922\/2nd. ed., 1924;\u00a0Atomic Theory and the Description of Nature<\/i>, University Press, Cambridge, 1934\/reprint 1961;\u00a0The Unity of Knowledge<\/i>, Doubleday & Co., New York, 1955.<\/p>\n
During the Nazi occupation of Denmark in World War II, Bohr escaped to Sweden and spent the last two years of the war in England and America, where he became associated with the Atomic Energy Project. In his later years, he devoted his work to the peaceful application of atomic physics and to political problems arising from the development of atomic weapons. In particular, he advocated a development towards full openness between nations. His views are especially set forth in his\u00a0Open Letter to the United Nations<\/i>, June 9, 1950.<\/p>\n
Until the end, Bohr\u2019s mind remained alert as ever; during the last few years of his life he had shown keen interest in the new developments of molecular biology. The latest formulation of his thoughts on the problem of Life appeared in his final (unfinished) article, published after his death: \u201cLicht und Leben-noch einmal\u201d,\u00a0Naturwiss<\/i>., 50 (1963) 72: (in English: \u201cLight and Life revisited\u201d,\u00a0ICSU Rev<\/i>., 5 ( 1963) 194).<\/p>\n
Niels Bohr was President of the Royal Danish Academy of Sciences, of the Danish Cancer Committee, and Chairman of the Danish Atomic Energy Commission. He was a Foreign Member of the Royal Society (London), the Royal Institution, and Academies in Amsterdam, Berlin, Bologna, Boston, G\u00f6ttingen, Helsingfors, Budapest, M\u00fcnchen, Oslo, Paris, Rome,\u00a0Stockholm, Uppsala, Vienna, Washington, Harlem, Moscow, Trondhjem, Halle, Dublin, Liege, and Cracow. He was Doctor,\u00a0honoris causa<\/i>, of the following universities, colleges, and institutes:\u00a0(1923-1939)<\/i>\u00a0\u2013 Cambridge, Liverpool, Manchester, Oxford, Copenhagen, Edinburgh, Kiel, Providence, California, Oslo, Birmingham, London;\u00a0(1945-1962)<\/i>\u00a0\u2013 Sorbonne (Paris), Princeton, Mc. Gill (Montreal), Glasgow, Aberdeen, Athens, Lund, New York, Basel, Aarhus, Macalester (St. Paul), Minnesota, Roosevelt (Chicago, Ill.), Zagreb, Technion (Haifa), Bombay, Calcutta, Warsaw, Brussels, Harvard, Cambridge (Mass.), and Rockefeller (New York).<\/p>\n
Professor Bohr was married, in 1912, to Margrethe N\u00f8rlund, who was for him an ideal companion. They had six sons, of whom they lost two; the other four have made distinguished careers in various professions \u2013 Hans Henrik (M.D.), Erik (chemical engineer),\u00a0Aage\u00a0(Ph.D., theoretical physicist, following his father as Director of the Institute for Theoretical Physics), Ernest (lawyer).<\/p>\n
Niels Bohr died in Copenhagen on November 18, 1962.<\/p>\n