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Science and technology: Sample extended biographies
Baird, John Logie (1888–1946)
Scottish inventor who was the first person to televise an image, using mechanical (non-electronic) scanning. He also gave the first demonstration of colour television.
Baird was born in Helensburgh, Dunbartonshire, on 13 August 1888. He was educated at Larchfield Academy and later took an engineering course at the Royal Technical College, Glasgow. He then studied at Glasgow University, but World War I interrupted his final year there. Rejected as physically unfit for military service, Baird became a superintendent engineer with the Clyde Valley Electrical Power Company. In 1918 he gave up engineering because of ill-health and set himself up in business, marketing
successfully such diverse products as patent socks, confections, and soap in Glasgow, London, and the West Indies. Persistent ill-health, leading to a complete physical and nervous breakdown in 1923, forced him to retire to Horsham in Sussex.
Many inventors had patented their ideas about television – the electrical transmission of images in motion simultaneously with accompanying sound – but only a few, including Baird, pursued a practical study of the problem based on the use of mechanical scanners. In 1907 Boris Rosing had proposed that, in a television system that used mirror-scanning in the camera, a cathode-ray tube with a fluorescent screen should be fitted into the receiver. In 1911 A A Campbell Swinton had suggested that magnetically deflected cathode-ray tubes should be used both in the camera and the receiver.
On his retirement, Baird concentrated on solving the problems of television. Having little money, his first apparatus was crude and makeshift, set up on a washstand in his attic room. A tea-chest formed the base of his motor, a biscuit tin housed the projection lamp, and cheap cycle-lamp lenses were incorporated into the design. The whole contraption was held together by darning needles, pieces of string, and scrap wood. Yet within a year he had succeeded in transmitting a flickering image of the outline of a Maltese cross over a distance of a few metres.
Baird took his makeshift apparatus to London where, in one of two attic rooms in Soho, he proceeded to improve it. In 1925 he achieved the transmission of an image of a recognizable human face and the following year, on 26 January, he gave the world's first demonstration of true television before an audience of about 50 scientists at the Royal Institution, London. Baird used a mechanical scanner that temporarily changed an image into a sequence of electronic signals that could then be reconstructed on a screen as a pattern of half-tones. The neon discharge lamp Baird used offered a simple means for the electrical modulation of light at the receiver. His first pictures were formed of only 30 lines repeated approximately ten times a second. The results were crude but it was the start of television as a practical technology.
By 1927, Baird had transmitted television over 700 km/435 mi of telephone line between London and Glasgow and soon after made
the first television broadcast using radio, between London and the SS Berengaria , halfway across the Atlantic Ocean. He also made the first transatlantic television broadcast between the UK and the USA, when signals transmitted from the Baird station in Coulson, Kent, were picked up by a receiver in Hartsdale, New York.
By 1928 Baird had succeeded in demonstrating colour television. The simplest way to reproduce a colour image is to produce the red, blue, and green primary images separately and then to superimpose them so that the eye merges the three images into one full-colour picture. Baird used three projection tubes arranged so that each threw a picture on to the same screen. By using only one amplifier chain and one cathode-ray tube that sequentially amplified the red, blue, and green signals, he overcame the problem of overregistration of the three images and matched the three channels. He used two rotating discs – each with segments of red-, green-, and blue-light filters, rotating synchronously before the camera tube and the receiver tube. Each primary-coloured filter remained over the tube face for the period of one field. Although partly successful, Baird's method had two major drawbacks. One was that the picture being transmitted consisted mainly of tones of one hue, say green, then the other two fields (red and blue) showed as black and each green field was succeeded by black ones, resulting in excessive flickering. The other was that the system required three times the bandwidth available.
Baird's black-and-white system was used by the BBC in an experimental television service in 1929. At first, the sound and vision were transmitted alternately, but by 1930 it was possible to broadcast them simultaneously. In 1936, when the public television service was started, his system was threatened by one promoted by Marconi–EMI. The following year the Baird system was dropped in favour of the Marconi electronic system, which gave a better definition.
Despite his bitter disappointment, Baird continued his experimental work in colour television. By 1939 he had demonstrated colour television using a cathode-ray tube which he had adapted as the most successful method for producing a well-defined and brilliant image. Baird's inventive and engineering abilities were widely recognized. In 1937, he became the first British subject to receive the gold medal of the International Faculty of Science. The same year, he was elected a Fellow of the Royal Institute of
Edinburgh, where a plaque was erected to commemorate his demonstration of true television in 1926. Baird also became an Honorary Fellow of the Royal Society of Edinburgh, a Fellow of the Physical Society, and an Associate of the Royal Technical College.
He continued his research on stereoscopic and large screen television until his death, at Bexhill-on-Sea, Sussex, on 14 June 1946.
Bohr, Niels Henrik David (1885–1962)
Danish physicist who established the structure of the atom. For this achievement he was awarded the 1922 Nobel Prize for Physics. Bohr made another very important contribution to atomic physics by explaining the process of nuclear fission.
Bohr was born in Copenhagen on 7 October 1885. His father, Christian Bohr, was professor of physiology at the University of Copenhagen and his younger brother Harald became an eminent mathematician. Niels Bohr was a less brilliant student than his brother but a careful and thorough investigator. His first research project, completed in 1906, resulted in a precise determination of the surface tension of water and gained him the gold medal of the Academy of Sciences. In 1911, he was awarded his doctorate for a theory accounting for the behaviour of electrons in metals.
In the same year, Bohr went to Cambridge, England, to study under J J Thomson, who showed little interest in Bohr's electron theory so, in 1912, Bohr moved to Manchester to work with Ernest Rutherford, who was making important investigations into the structure of the atom. Bohr developed models of the atom in which electrons are disposed in rings around the nucleus, a first step towards an explanation of atomic structure.
Bohr returned to Copenhagen as a lecturer at the university in 1912, and in 1913 developed his theory of atomic structure by applying the quantum theory to the observations of radiation emitted by atoms. He then went back to Manchester to take up a lectureship offered by Rutherford, enabling him to continue his investigations in ideal conditions. However, the authorities in Denmark enticed him back with a professorship and then built the Institute of Theoretical Physics in Copenhagen for him. He became director of the institute in 1920, holding this position until his death. The institute rapidly became a centre for theoretical physicists from throughout the world, and such figures as Wolfgang Pauli and Werner Heisenberg developed Bohr's work there, resulting in the theories of quantum and wave mechanics that more fully explain the behaviour of electrons within atoms.
The year 1922 marked not only the award of the Nobel Prize for Physics but also a triumphant vindication of Bohr's atomic theory, which he used to predict the existence of a hitherto-unknown element. The element was discovered at the institute and given the name hafnium.
In the 1930s, interest in physics turned towards nuclear reactions and in 1939 Bohr proposed his liquid-droplet model for the nucleus that was able to explain why a heavy nucleus could undergo fission following the capture of a neutron. Working from
experimental results, Bohr was able to show that only the isotope uranium-235 would undergo fission with slow neutrons.
When Denmark was occupied by the Germans in 1940 early in World War II, Bohr took an active part in the resistance movement. In 1943, he escaped to Sweden with his family in a fishing boat – not without danger – and then went to the UK and on to the USA. He became involved in the development of the atomic bomb, helping to solve the physical problems involved, but later becoming a passionate advocate for the control of nuclear weapons. Among his efforts to persuade politicians to adopt rational and peaceful
solutions was a famous open letter addressed to the United Nations in 1950 pleading for an 'open world' of free exchange of people and ideas.
In 1952 Bohr was instrumental in creating the European Centre for Nuclear Research (CERN), now at Geneva, Switzerland. He died in Copenhagen on 18 November 1962. In addition to his scientific papers, Bohr published three volumes of essays: Atomic Theory and the Description of Nature (1934), Atomic Physics and Human Knowledge (1958), and Essays 1958–1962 on Atomic Physics and Human Knowledge (1963).
Bohr's first great inspiration came from working with Rutherford, who had proposed a nuclear theory of atomic structure from his work on the scattering of alpha rays in 1911. It was not, however, understood how electrons could continually orbit the nucleus without radiating energy, as classical physics demanded. Ten years earlier Max Planck had proposed that radiation is emitted or absorbed by atoms in discrete units, or quanta, of energy. Bohr applied this quantum theory to the nuclear atom to explain why elements emit radiation at precise frequencies that give set patterns of spectral lines. He postulated that an atom may exist in only a certain number of stable states, each with a certain amount of energy; the emission or absorption of energy may occur only with a transition from one stable state to another. Electrons normally orbit the nucleus without emitting or absorbing energy. When a transition occurs, an electron moves to a lower or higher orbit depending on whether it emits or absorbs energy. In so doing, a set number of quanta of energy are emitted or absorbed at a particular frequency. Bohr developed these ideas to show that the nuclei of atoms are surrounded by shells of electrons, each assigned particular sets of quantum numbers according to their orbits. Bohr's theory was used to determine the frequencies of spectral lines produced by elements and succeeded brilliantly. It also enabled him to explain the groups of the periodic table in terms of elements with similar electron structures, which led to the prediction and discovery of hafnium.
In developing a model for the nucleus, Bohr conceived of the nuclear particles being pulled together by short-range forces rather as the molecules in a drop of liquid are attracted to one another. The extra energy produced by the absorption of a neutron may cause the nuclear particles to separate into two groups of approximately the same size, thus breaking the nucleus into two smaller nuclei – as happens in nuclear fission. The model was vindicated when Bohr correctly predicted the differing behaviour of nuclei of uranium-235 and uranium-238 from the fact that the number of neutrons in each nucleus is odd and even respectively.
Niels Bohr gained not only a love of science from his father but also a philosophical insight into the nature of knowledge that enabled him to question accepted theories and seek new explanations. By reconciling Rutherford's nuclear model of the atom with
Planck's quantum theory, he was able to produce a valid model for the atom completely at odds with classical physics. However, this did not prevent him from using a classical model to explain the structure and behaviour of the nucleus. Our present knowledge of the atom and the nucleus thus rests on the fundamental discoveries made by Bohr's restless and ingenious mind.
Fibonacci, Leonardo (c. 1180–c. 1250)
also known as Leonardo of Pisa
Italian mathematician whose writings were influential in introducing and popularizing the Indo-Arabic numeral system, and whose work in algebra, geometry, and theoretical mathematics was far in advance of the contemporary European standards.
Fibonacci was born in Pisa in about 1180, the son of a member of the government of the republic of Pisa. When Fibonacci was 12 years old, his father was made administrator of Pisa's trading colony in Algeria, and it was there – in a town now called Bougie – that he was taught the art of calculating, using the commercial North African medium of Indo-Arabic numerals. His teacher, who remains completely unknown, seems to have imparted to him not only an excellently practical and well-rounded fundamental grounding in mathematics, but also a true scientific curiosity.
Having achieved maturity, Fibonacci travelled extensively, both for business and for pleasure, spending time in Italy, Syria, Egypt, Greece, and elsewhere. Wherever he went he observed and analysed the arithmetical systems used in local commerce, studying through discussion and argument with the native scholars of the countries he visited. He returned to Pisa in about the year 1200 and began his mathematical writings. Little more is known of him, although in 1225 he won a mathematical tournament in the presence of the Holy Roman Emperor Frederick II at the court of Pisa. A marble tablet dated 1240 appears to refer to him as having been awarded an annual pension following his valuable accountancy services to the state. He is assumed to have died in Pisa in about 1250.
Two years after finally settling in Pisa, Fibonacci produced his most famous book, Liber abaci/The Book of the Calculator. In four parts, and revised by him a quarter of a century later (in 1228), it was a thorough treatise on algebraic methods and problems in which he strongly advocated the introduction of the Indo-Arabic numeral system, comprising the figures 1 to 9, and the innovation of the 'zephirum' – the figure 0 (zero). Dealing with operations in whole numbers systematically, he also proposed the idea of a bar (solidus) for fractions, and went on to develop rules for converting fraction factors into the sum of unit factors. (However, his expression of fractions followed the Arabic practice – on the left of the relevant integral.) At the end of the first part of the book, he presented tables for multiplication, prime numbers, and factoring numbers. In the second part, he demonstrated mathematical applications to commercial transactions. In part three he gave many examples of recreational mathematical problems of the type enjoyed today, leading up to a thesis on series from which, in turn, he derived what is now called the Fibonacci series. This is a sequence in which each term after the first two is the sum of the two terms immediately preceding it – 1, 1, 2, 3, 5, 8, 13, 21, ... for example – and which has been found to have many significant and interesting properties. And in the final part of the book Fibonacci, a student of Euclid, applied the algebraic method. The Liber abaci remained a standard text for the next two centuries.
In 1220 he published Practica geometriae, a book on geometry that was of fundamental significance to future studies of the subject, and that (to some commentators, at least) seems to be based on a work of Euclid now lost. In it, Fibonacci used algebraic methods to solve many arithmetical and geometrical problems. In Flos/Flower, published four years later, he considered indeterminate problems in a way that had not properly been carried out since the work of Diophantus in the 2nd century
AD, and again demonstrated Euclidean methodology combined with techniques of Chinese and Arabic origin (learned during his travels many years before) in solving determinate problems. In both Liber quadratorum/The Book of Squares and in a separate letter to the philosopher Theodorus, Fibonacci dealt with some problems set by John of Palermo (one of which was the one he solved in front of the emperor); his treatments show unusual mathematical skill and originality.
The complete works of Fibonacci were edited in the 19th century by B Boncompagni, and published in two volumes under the title Scritti di Leonardo Pisano.
Hubble, Edwin (Powell) (1889–1953)
US astronomer who studied extragalactic nebulae and demonstrated them to be galaxies like our own. He found the first evidence for the expansion of the universe, in accordance with the cosmological theories of Georges Lemaître and Willem de Sitter, and his work led to an enormous expansion of our perception of the size of the universe.
Hubble was born in Marshfield, Missouri, on 20 November 1889. He went to high school in Chicago and then attended the University of Chicago where his interest in mathematics and astronomy was influenced by George Hale and Robert Millikan. After receiving his bachelor's degree in 1910, he became a Rhodes scholar at Queen's College, Oxford, where he took a degree in jurisprudence in 1912. When he returned to the USA in 1913, he was admitted to the Kentucky Bar, and he practised law for a brief period before returning to Chicago to take a research post at the Yerkes Observatory 1914–17.
In 1917 Hubble volunteered to serve in the US infantry and was sent to France at the end of World War I. He remained on active service in Germany until 1919, when he was able to return to the USA and take up the earlier offer made to him by Hale of a post as astronomer at the Mount Wilson Observatory near Pasadena, where the 2.5-m/100-in reflecting telescope had only recently been made operational. Hubble worked at Mount Wilson for the rest of his career, and it was there that he carried out his most important work. His research was interrupted by the outbreak of World War II, when he served as a ballistics expert for the US War Department. He was awarded the Gold Medal of the Royal Astronomical Society in 1940, and received the Presidential Medal for Merit in 1946. He was active in research until his last days, despite a heart condition, and died in San Marino, California, on 28 September 1953.
While Hubble was working at the Yerkes Observatory, he made a careful study of nebulae, and attempted to classify them into intra- and extragalactic varieties. At that time there was great interest in discovering what other structures, if any, lay beyond our Galaxy. The mysterious gas clouds, known as the smaller and larger Magellanic Clouds, which had first been systematically catalogued by Charles Messier and called 'nebulae', were good extragalactic candidates and were of great interest to Hubble. He had been particularly inspired by Henrietta Leavitt's work on the Cepheid variable stars in the Magellanic Clouds; and later work by Harlow Shapley, Henry Russell, and Ejnar Hertzsprung on the distances of these stars from the Earth had demonstrated that the universe did not begin and end within the confines of our Galaxy. Hubble's doctoral thesis was based on his studies of nebulae, but he found it frustrating because he knew that more definite information depended upon the availability of telescopes of greater light-gathering power and with better resolution.
After World War I, with the 2.5-m/100-in reflector at Mount Wilson at his disposal, Hubble was able to make significant advances in his studies of nebulae. He found that the source of the light radiating from nebulae was either stars embedded in the nebular gas or stars that were closely associated with the system. In 1923 he discovered a Cepheid variable star in the Andromeda nebula. Within a year he had detected no fewer than 36 stars within that nebula alone, and found that 12 of these were Cepheids. These 12 stars could be used, following the method applied to the Cepheids that Leavitt had observed in the Magellanic Clouds, to determine the distance of the Andromeda nebula. It was approximately 900,000 light years away, much more distant than the outer boundary of our own Galaxy – then known to be about 100,000 light years in diameter.
Hubble discovered many gaseous nebulae and many other nebulae with stars. He found that they contained globular clusters, novae, and other stellar configurations that could also be found within our own Galaxy. In 1924 he finally proposed that these nebulae were in fact other galaxies like our own, a theory that became known as the 'island universe'. From 1925 onwards he studied the structures of the galaxies and classified them according to their morphology into regular and irregular forms. The regular nebulae comprised 97% of them and appeared either as ellipses or as spirals, and the spirals were further divided into normal and barred types. All the various shapes made up a continuous series, which Hubble saw as an integrated 'family'. The irregular forms comprised only 3% of the nebulae he studied. By the end of 1935, Hubble's work had extended the horizons of the universe to 500 million light years.
Having classified the various kinds of galaxies that he observed, Hubble began to assess their distances from us and the speeds at which they were receding. The radial velocity of galaxies had been studied by several other astronomers, in particular by Vesto Slipher. Hubble analysed his data, and added some new observations. In 1929 he found, on the basis of information for 46 galaxies, that the speed at which the galaxies were receding (as determined from their spectroscopic red shifts) was directly correlated with their distance from us. He found that the more distant a galaxy was, the greater was its speed of recession – now known as Hubble's law. This astonishing relationship inevitably led to the conclusion that the universe is expanding, as Lemaître had also deduced from Albert Einstein's general theory of relativity.
This data was used to determine the portion of the universe that we can ever come to know, the radius of which is called the Hubble radius. Beyond this limit, any matter will be travelling at the speed of light, and so communication with it will never be possible. The data on galactic recession was also used to determine the age and the diameter of the universe, although at the time
both of these calculations were marred by erroneous assumptions, which were later corrected by Walter Baade. The ratio of the velocity of galactic recession to distance has been named the Hubble constant, and the modern value for the speed of galactic recession is 530 km/330 mi per sec – very close to Hubble's original value of 500 km/310 mi per sec.
During the 1930s, Hubble studied the distribution of galaxies and his results supported the idea that their distribution was isotropic. They also clarified the reason for the 'zone of avoidance' in the galactic plane. This effect was caused by the quantities of dust and diffuse interstellar matter in that plane.
Among his later studies was a report made in 1941 that the spiral arms of the galaxies probably did 'trail' as a result of galactic rotation, rather than open out. After World War II Hubble became very much an elder statesman of US astronomy. He was involved in the completion of the 5-m/200-in Hale Telescope at Mount Palomar, which was opened in 1948. One of the original intentions for this telescope was the study of faint stellar objects, and Hubble used it for this purpose during his few remaining years.
Humboldt, (Friedrich Wilhelm Heinrich) Alexander (1769–1859)
Baron von Humboldt
German geophysicist, botanist, geologist, and writer; a founder of ecology.
Born in Berlin on 14 September 1769, Humboldt was the son of a Prussian soldier who wanted him to pursue a political career. Humboldt had other ideas. Preferring science, he studied at Göttingen University, proceeding to Abraham Werner's Freiberg mining school and spending two years as a mines engineer. In the 1790s he travelled widely in Europe, before setting out, in 1799, with the French botanist A Bonpland, on a pioneering and immensely productive expedition across Latin America. Studying physical geography above all, but also collecting vast quantities of geological, botanical, and zoological material, Humboldt covered some 9,600 km/6,000 mi. His expedition included travelling up the Orinoco and the Magdalena, passing a year in Mexico and some time in Cuba, visiting the sources of the Amazon, and cutting across the continent to the Cordilleras and on to Quito and Lima.
He returned to Europe in 1804 laden with scientific specimens, and spent the next 20 years writing up his results, not least in his Narrative of Travels (1818–19). Humboldt aimed to erect a new science, a 'physics of the globe', analysing the deep physical interconnectedness of all terrestrial phenomena. He believed physical relief should be grasped in terms of Earth history, and likewise that geological phenomena were to be understood in terms of more basic physical causes (for example, terrestrial magnetism or rotation). Showing a phenomenal ability to keep abreast of developments in geophysics, meteorology, and geography, he patiently amassed evidence of comparable geological phenomena from every continent.
Humboldt arrived at numerous important findings. On the basis of studies of Pacific coastal currents, he was one of the first to
propose a Panama canal. In meteorology, he introduced isobars and isotherms on weathermaps, made a general study of global temperature and pressure, and finally instituted a worldwide programme for compiling magnetic and weather observations. His studies of US volcanoes demonstrated they corresponded to underlying geological faults; on that basis he deduced that volcanic action had been pivotal in geological history and that many rocks were igneous in origin. In 1804, he discovered that the Earth's magnetic field decreased from the poles to the Equator.
His most popular work, Cosmos, begun in 1845 at the age of 76, is a profound and moving statement of our relationship with the Earth, and of the relations between physical environment and flora and fauna. A gracious polymath held in universal respect, Humboldt proved enormously influential in study of the globe, both as an explorer and as a theorist. As one who set out to
chart the history of human interrelations with planet Earth, he may be called the founder of ecology. He died in Berlin on 6 May 1859.
Mendel, Gregor Johann (1822–1884)
Austrian geneticist and monk who discovered the basic laws of heredity, thereby laying the foundation of modern genetics – although the importance of his work was not recognized until after his death.
Mendel was born Johann Mendel on 22 July 1822 in Heinzendorf, Austria (now Hyncíce in the Czech Republic), the son of a peasant farmer. He studied for two years at the Philosophical Institute in Olmütz (now Olomouc), after which, in 1843, he entered the Augustinian monastery in Brünn, Moravia (now Brno), taking the name Gregor. In 1847 he was ordained a priest. During his religious training, Mendel taught himself a certain amount of science and for a short time he was a teacher of Greek and mathematics at the secondary school in Znaim (now Znojmo) near Brünn. In 1850 he tried to pass an examination to obtain a teaching licence but failed, and in 1851 he was sent by his abbot to the University of Vienna to study physics, chemistry, mathematics, zoology, and botany. Mendel left the university in 1853 and returned to the monastery in Brünn in 1854. He then taught natural science in the local technical high school until 1868, during which period he again tried, and failed, to gain a teaching certificate that would have enabled him to teach in more advanced institutions. It was also in the period 1854–68 that Mendel performed most of his scientific work on heredity. He was elected abbot of his monastery at Brünn in 1868, and the administrative duties involved left him little time for further scientific investigations. Mendel remained abbot at Brünn until his death on 6 January 1884.
Mendel began the experiments that led to his discovery of the basic laws of heredity in 1856. Much of his work was performed on the edible pea (Pisum), which he grew in the monastery garden. He carefully self-pollinated and wrapped (to prevent accidental pollination by insects) each individual plant, collected the seeds produced by the plants, and studied the offspring of these seeds. He found that dwarf plants produced only dwarf offspring and that the seeds produced by this second generation also produced only dwarf offspring. With tall plants, however, he found that both tall and dwarf offspring were produced and that only about one-third of the tall plants bred true, from which he concluded that there were two types of tall plants, those that bred true and those that did not. Next he cross-bred dwarf plants with true-breeding tall plants, planted the resulting seeds and then self-pollinated each plant from this second generation. He found that all the offspring in the first generation were tall but that the offspring from the self-pollination of this first generation were a mixture of about one-quarter true-breeding dwarf plants, one-quarter true-breeding tall plants and one-half non-true-breeding tall plants. Mendel also studied other characteristics in pea plants, such as flower colour, seed shape, and flower position, finding that, as with height, simple laws governed the inheritance of these traits. From his findings Mendel concluded that each parent plant contributes a factor that determines a particular trait and that the pairs of factors in the offspring do not give rise to an amalgamation of traits. These conclusions, in turn, led him to formulate his famous law of segregation and law of independent assortment of characters, which are now recognized as two of the fundamental laws of heredity.
Mendel reported his findings to the Brünn Society for the Study of Natural Science in 1865 and in the following year he published 'Experiments with plant hybrids', a paper that summarized his results. But the importance of his work was not recognized at the time, even by the eminent botanist Karl Wilhelm von Nägeli, to whom Mendel sent a copy of his paper. It was not until
1900, when his work was rediscovered by Hugo de Vries, Carl Erich Correns, and Erich Tschermak von Seysenegg, that Mendel achieved fame – 16 years after his death.
Mendeleyev, Dmitri Ivanovich (1834–1907)
Russian chemist whose name will always be linked with his outstanding achievement, the development of the periodic table. He was the first chemist to understand that all elements are related members of a single ordered system. He converted what had hitherto been a highly fragmented and speculative branch of chemistry into a true, logical science.
Mendeleyev was born in Tobol'sk, Siberia, on 7 February 1834, the youngest of the 17 children of the head of the local high school. His father went blind when Mendeleyev was still a child, and the family had to rely increasingly on their mother for support. He was educated locally but could not gain admission to any Russian university (despite his mother's attempts on his behalf with the authorities at Moscow) because of the supposedly backward attainments of those educated in the provinces. In 1855 he finally qualified as a teacher at the Pedagogical Institute in St Petersburg. He took an advanced degree course in chemistry, and in 1857 obtained his first university appointment.
In 1859 he was sent by the government for further study at the University of Heidelberg in Germany, where he made valuable contact with the Italian chemist Stanislao Cannizzaro, whose insistence on a proper distinction between atomic and molecular masses influenced Mendeleyev greatly. In 1861 he returned to St Petersburg and became professor of general chemistry at the Technical Institute there in 1864. He could find no textbook adequate for his students' needs and so he decided to produce his own. The resulting Principles of Chemistry (1868–70) won him international renown; it was translated into English in 1891 and
1897.
Mendeleyev began work on his periodic law in the late 1860s, and he went on to conduct research in various other fields. Then in 1890 he chose to be a spokesperson for students who were protesting against unjust conditions. For these allegedly improper activities he was retired from the university and became controller of the Bureau for Weights and Measures, although from 1893 he received no other professorial appointment. He died in St Petersburg on 2 February 1907, five days before his 73rd birthday. His nomination for the 1906 Nobel Prize for Chemistry failed by one vote – the award went to the French chemist Henri Moissan (1852–1907) – but his name became recorded in perpetuity 50 years later when element number 101 was called mendelevium.
Before Mendeleyev produced his periodic law, understanding of the chemical elements had long been an elusive and frustrating task. The attempts by various chemists to put the whole field into some intelligible reference system had acted rather like the progressively stronger lenses of a microscope in bringing a sensed but unseen object into clear vision. According to Mendeleyev the
properties of the elements, as well as those of their compounds, are periodic functions of their atomic weights (relative atomic masses). In 1869 he stated that 'the elements arranged according to the magnitude of atomic weights show a periodic change of properties'. Other chemists, notably Lothar Meyer in Germany, had meanwhile come to similar conclusions, Meyer publishing his findings independently.
Mendeleyev compiled the first true periodic table, listing all the 63 elements then known. Not all elements would 'fit' properly using the atomic masses of the time, so he altered indium from 76 to 114 (modern value 114.8) and beryllium from 13.8 to 9.2 (modern value 9.013). In 1871 he produced a revisionary paper showing the correct repositioning of 17 elements.
Also in order to make the table work Mendeleyev had to leave gaps, and he predicted that further elements would eventually be discovered to fill them. These predictions provided the strongest endorsement of the periodic law. Three were discovered in Mendeleyev's lifetime: gallium in 1871, scandium in 1879, and germanium in 1886, all with properties that tallied closely with those he had assigned to them.
Far-sighted though Mendeleyev was, he had no notion that the periodic recurrences of similar properties in the list of elements reflect anything in the structures of their atoms. It was not until the 1920s that it was realized that the key parameter in the
periodic system is not the atomic mass but the atomic number of the elements – a measure of the number of nuclear protons or electrons in the stable atom. Since then great progress has been made in explaining the periodic law in terms of the electronic structures of atoms and molecules.
Among Mendeleyev's other investigations were the specific volumes of gases and the conditions that are necessary for their
liquefaction. Following visits to the oilfields of the Caucasus and in the USA he examined the origins of petroleum. He was convinced that the future held great possibilities for human flight, and in 1887 he made an ascent in a balloon to observe an eclipse of the Sun. He farmed a small estate and applied his scientific knowledge to improve the yield and quality of crops, an endeavour invaluable for Russia's predominantly agricultural economy.
Pavlov, Ivan Petrovich (1849–1936)
Russian physiologist, best known for his systematic studies of the conditioning of dogs and other animals. For his observations on the gastrointestinal secretion in animals he received the 1904 Nobel Prize for Physiology or Medicine.
Pavlov was born in Ryazan on 24 September 1849. He decided to follow in the footsteps of his father, the local priest, and entered a theological college. In 1870, however, he left the seminary to study chemistry and physiology at the University of St Petersburg. There he was taught by the chemists Dmitri Mendeleyev and Alexander Butlerov (1828–1886). He received his medical degree in 1879 from the Imperial Medical Academy, St Petersburg, and his PhD from the military academy there in 1883. From 1884 to 1886 he studied cardiovascular and gastrointestinal physiology in Germany, under Karl Ludwig in Leipzig and Rudolf Heidenhain in Breslau (now Wroclaw in Poland). He researched at the Botkin laboratory in St Petersburg 1888–90 and in 1890 was appointed professor of physiology at the Imperial Medical Academy, where he remained until he resigned in 1924. He died in St Petersburg (then named Leningrad) on 27 February 1936.
Pavlov's first unaided research was on the physiology of the circulatory system, studying cardiac physiology and the regulation of blood pressure. Using experimental animals, he became a surgeon of some distinction, a typical example of his experiments being the dissection of the cardiac nerves of a living dog to show how the nerves that leave the cardiac plexus control heartbeat strength.
During the years from 1890 to 1900, Pavlov investigated the secretory mechanisms of digestion. He developed an operation to prepare an ancillary miniature stomach or pouch, isolated from salivary and pancreatic secretions but with its vagal-nerve supply intact. In this way he was able to observe the gastrointestinal secretion of a living animal.
Pavlov then went on to develop the idea of the conditional reflex – the discovery for which he is most famous. Pavlov confined a dog in a soundproof room, in order to ensure that there were no distracting influences such as extraneous sounds and smells. The dog was held in a loose harness so that it could not move about too much. Food was delivered to it by an automatic apparatus operated from outside the room, so that the dog was fed at an appropriate moment without direct interference from the person directing the experiment. The flow of saliva from the dog's parotid gland was collected in a small measuring tube attached to the animal's cheek. The experiment was continued until the dog became used to the artificial situation. Pavlov discovered that if a neutral stimulus, such as a bell, was presented simultaneously with a natural stimulus to salivate (such as the sight of food) and the combination repeated often enough, the sound of the bell alone caused salivation.
Pavlov termed salivation the 'unconditioned reflex' and food the 'unconditioned stimulus'. The sound of the bell is the 'conditioned stimulus' and the salivation caused by the bell alone the 'conditioned reflex'. Many inborn reflexes may be conditioned by Pavlov's method, including responses involving the skeletal muscles (knee-jerking and blinking), as well as responses of the smooth muscles and glands.
A similar approach was developed in Pavlov's work relating to human behaviour and the nervous system, all the time emphasizing the importance of conditioning. He deduced that the inhibitive behaviour of a psychotic person is a means of self-protection. The person shuts out the world and, with it, all damaging stimuli. Following this theory, the treatment of psychiatric patients in Russia involved placing a sick person in completely calm and quiet surroundings.
Pavlov's study of the normal animal in natural conditions enabled him to add greatly to scientific knowledge. He also demonstrated the necessity of providing the right situation for completely objective study and measurement of behaviour, and greatly improved operative and post-operative conditions for animals.
In 1897 Pavlov summarized his findings in his Nobel prize-winning work, Lectures on the Work of the Principal Digestive Gland.
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