A Dictionary of Science SIXTH EDITION 1 1 Great Clarendon Street, Oxford OX2 6DP Oxford University Press is a department of the University of Oxford. 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Printed in Great Britain by Clays Ltd, St Ives plc ISBN 978–0–19–956146–9 10 9 8 7 6 5 4 3 2 1 Preface This sixth edition of A Dictionary of Science, like its predecessors, aims to provide school and first-year university students with accurate explanations of any unfamiliar words they might come across in the course of their studies, in their own or adjacent disciplines. For example, students of the physical sciences will find all they are likely to need to know about the life sciences, and vice versa. The dictionary is also designed to provide non-scientists with a useful reference source to explain the scientific terms that they may encounter in their work or in their general reading. At this level the dictionary provides full coverage of terms, concepts, and laws relating to physics, chemistry, biology, biochemistry, palaeontology, and the earth sciences. There is also coverage of key terms in astronomy, cosmology, mathematics, biotechnology, and computer technology. In addition, the dictionary includes: • over 160 short biographical entries on the most important scientists in the history of the subject • ten features (each of one or two pages) on concepts of special significance in modern science • ten chronologies showing the development of selected concepts, fields of study, and industries • eight Appendices, including the periodic table, tables of SI units and conversion tables to and from other systems of units, summary classifications of the plant and animal kingdoms, and useful websites. For this sixth edition nearly 700 new entries have been added to the text, incorporating recent advances in all the major fields and increased coverage of astronomy, forensic chemistry, and computing. In compiling the dictionary, the contributors and editors have made every effort to make the entries as concise and comprehensible as possible, always bearing in mind the needs of the readers. Particular features of the book are its lack of unnecessary scientific jargon and its extensive network of cross-references. An asterisk placed before a word used in an entry indicates that this word can be looked up in the dictionary and will provide further explanation or clarification. However, not every word that is defined in the dictionary has an asterisk placed before it when it is used in an entry. Some entries simply refer the reader to another entry, indicating either that they are synonyms or abbreviations or that they are most conveniently explained in one of the dictionary’s longer articles. Synonyms and abbreviations are usually placed within brackets immediately after the headword. Terms that are explained within an entry are highlighted by being printed in boldface type. Where appropriate, the entries have been supplemented by fully labelled line-drawings or tables in situ. JD EM 2009 Credits Editors John Daintith BSc, PhD Elizabeth Martin MA Advisers B. S. Beckett BSc, BPhil, MA(Ed) R. A. Hands BSc Michael Lewis MA Contributors Richard Batley PhD, MInstP Malcolm Hart BSc, MIBiol Tim Beardsley BA Robert S. Hine BSc, MSc Lionel Bender BSc Elaine Holmes BSc, PhD John Clark BSc Valerie Illingworth BSc, MPhil H. M. Clarke MA, MSc Anne Lockwood BSc W. M. Clarke BSc J. Valerie Neal BSc, PhD Derek Cooper PhD, FRIC R. A. Prince MA John Cullerne DPhil Richard Rennie BSc, MSc, PhD R. Cutler BSc Michael Ruse BSc, PhD E. K. Daintith BSc Jackie Smith BA D. E. Edwards BSc, MSc Brian Stratton BSc, MSc A. J. H. Goddard PhD, MIMechE, Elizabeth Tootill BSc, MSc FInstNucE, FInstP, MSRP David Eric Ward BSc, MSc, PhD William Gould BA Edmund Wright DPhil Contents Preface vii Credits viii A Dictionary of Science 1 Atomic Theory Chronology 63 The Big-Bang Theory (Feature) 86 Biochemistry Chronology 90 Cell Biology Chronology 144 Cosmology Chronology 200 Crystal Defects (Feature) 210 Electronics Chronology 275 El Niño (Feature) 284 Explosives Chronology 308 Genetically Modified Organisms (Feature) 352 Learning in Animals (Feature) 470 Microscopy Chronology 528 Moon Exploration Chronology 541 Magnetic Resonance Imaging (Feature) 569 Plastics Chronology 638 Polymers (Feature) 648 Refrigeration (Feature) 702 Solar System (Feature) 766 Optical Astronomical Telescopes (Feature) 809 Vitamins Chronology 863 Appendices SI units 893 Fundamental constants 895 The solar system 895 Geological time scale 896 Simplified classification of land plants 897 Simplified classification of the animal kingdom 898 The periodic table 899 Useful websites 900 A aa See. tion. The angular displacement α=v/c, AAR See  . wherevis the earth’s orbital velocity and cis the speed of light. AAS See  . abiogenesis The origin of living from ab- A preÜx attached to the name of a prac- nonliving matter, as by *biopoiesis. See also tical electrical unit to provide a name for a  . unit in the electromagnetic system of units (see ), e.g. abampere, abiotic factor Any of the nonliving factors abcoulomb, abvolt. The preÜx is an abbrevi- that make up the abiotic environment in which living organisms occur. They include ation of the word ‘absolute’ as this system is all the aspects of climate, geology, and at- also known as the absolute system.Compare -. In modern practice both absolute and mosphere that may affect the biotic environ- ment.Compare . electrostatic units have been replaced by *SI units. abomasum The fourth andÜnal chamber abdomen The posterior region of the body of the stomach of ruminants. It leads from trunk of animals. In vertebrates it contains the *omasum and empties into the small in- the stomach and intestines and the organs of testine. The abomasum is referred to as the excretion and reproduction. It is particularly ‘true stomach’ as it is in this chamber that well deÜned in mammals, being separated protein digestion occurs, in acidic condi- from the *thorax by the *diaphragm. In tions.SeeR. many arthropods, such as insects and spi- ABO system One of the most important ders, it may be segmented. human *blood group systems. The system is Abelian group See. based on the presence or absence of *anti- gens A and B on the surface of red blood cells aberration 1.(in optics) A defect in the and of *antibodies against these in blood image formed by a lens or curved mirror. In serum. A person whose blood contains ei- chromatic aberration the image formed by a ther or both these antibodies cannot receive lens (but not a mirror) has coloured fringes a transfusion of blood containing the corre- as a result of the different extent to which sponding antigens as this would cause the light of different colours is refracted by glass. red cells to clump (see). The It is corrected by using an *achromatic lens. table overleaf illustrates the basis of the sys- Inspherical aberration, the rays from the tem: people of blood group O are described object come to a focus in slightly different as ‘universal donors’ as they can give blood positions as a result of the curvature of the to those of any of the other groups. See also lens or mirror. For a mirror receiving light  . strictly parallel with its axis, this can be cor- rected by using a parabolic surface rather abscisic acid A naturally occurring plant than a spherical surface. Spherical aberra- hormone that appears to be involved pri- tion in lenses is minimized by making both marily in seed maturation, stress responses surfaces contribute equally to the ray devia- (e.g. to heat and waterlogging), and in regu- tions, and can be lessened (though with re- lating closure of leaf pores (stomata). In duced image brightness) by the use of seeds, it promotes the synthesis of storage diaphragms to let light pass only through the protein and prevents premature germina- centre part of the lens. See also ; tion. In leaves, abscisic acid is produced in . 2.(in astronomy) The apparent dis- large amounts when the plant lacks sufÜ- placement in the position of a star as a result cient water, promoting closure of stomata of the earth’s motion round the sun. Light and hence reducing further water losses. It appears to come from a point that is slightly was formerly believed to play a central role displaced in the direction of the earth’s mo- in *abscission, hence the name. abscissa 2 a Group Antigens on red Antibodies Blood group of Blood group of cell surface in serum people donor can people donor can receive blood from give blood to A A anti-B A, O A, AB B B anti-A B, O B, AB AB A and B none A, B, AB, O AB O neither A nor B anti-A and O A, B, AB, O anti-B ABO system. abscissa SeeC . tral carbon atom is at the centre of a tetrahe- dron with the four groups at the corners and abscission The separation of a leaf, fruit, that the –H and –OH come out of the paper or other part from the body of a plant. It in- volves the formation of an abscission zone, and the –CHO and –CH2OH groups go into the paper. The resulting three-dimensional at the base of the part, within which a layer structure was taken to be that of d-glycer- of cells (abscission layer) breaks down. This process is suppressed so long as sufÜcient aldehyde and called D-glyceraldehyde. Any amounts of *auxin, a plant hormone,Ûow cboomn patooumn dh athvaint gc othnitsa cinosn aÜng uarsaytmiomn ebterlioc ncgasr- from the part through the abscission zone. However, if the auxinÛow declines, for ex- tcoo nthÜeg uDr-asteiorine sb. eOlonneg hsa tvoi nthge t hLe-s oepripeos.s iItte is ample due to injury or ageing, abscission is important to note that the preÜxes D- and L- activated. Ethylene (*ethene) acts as the pri- do not stand for dextrorotatory and laevoro- mary trigger for abscission, inducing cells in tatory (they are not the same as d- and l-). In the abscission zone to produce cellulase en- fact the arbitrary conÜguration assigned to zymes that degrade cell walls. D-glyceraldehyde is now known to be the absolute 1.Not dependent on or relative correct one for the dextrorotatory form, al- to anything else, e.g. *absolute zero. 2.De- though this was not known at the time. noting a temperature measured on an ab- However, all D-compounds are not dextro- solute scale, a scale of temperature based on rotatory. For instance, the acid obtained by absolute zero. The usual absolute scale now oxidizing the –CHO group of glyceraldehyde is that of thermodynamic *temperature; its is glyceric acid (1,2-dihydroxypropanoic unit, the kelvin, was formerly called the de- acid). By convention, this belongs to the gree absolute (°A) and is the same size as the D-series, but it is in fact laevorotatory; i.e. degree Celsius. In British engineering prac- its name can be written as D-glyceric acid tice an absolute scale with Fahrenheit-size orl-glyceric acid. To avoid confusion it is degrees has been used: this is the Rankine better to use + (for dextrorotatory) and – (for scale. laevorotatory), as in D-(+)-glyceraldehyde and D-(–)-glyceric acid. absolute alcohol See. The D–L convention can also be used with absolute conÜguration A way of denot- alpha amino acids (compounds with the ing the absolute structure of an optical iso- –NH2group on the same carbon as the mer (see ). Two conventions –COOH group). In this case the molecule is are in use: The D–L convention relates the imagined as being viewed along the H–C structure of the molecule to some reference bond between the hydrogen and the asym- molecule. In the case of sugars and similar metric carbon atom. If the clockwise order of compounds, the dextrorotatory form of the other three groups is –COOH, –R, –NH2, glyceraldehyde (HOCH2CH(OH)CHO), 2,3- the amino acid belongs to the D-series; oth- dihydroxypropanal) was used. The rule is as erwise it belongs to the L-series. This is follows. Write the structure of this molecule known as the CORN rule. down with the asymmetric carbon in the The R–S convention is a convention based centre, the –CHO group at the top, the –OH on priority of groups attached to the chiral on the right, the –CH2OH at the bottom, and carbon atom. The order of priority is I, Br, Cl, the –H on the left. Now imagine that the cen- SO3H, OCOCH3, OCH3, OH, NO2, NH2, 3 absolute value (cid:1)(cid:2)(cid:3) (cid:1)(cid:2)(cid:3) (cid:1)(cid:2)(cid:3) a (cid:2) (cid:1) (cid:3)(cid:2) (cid:1) (cid:2)(cid:1)(cid:3)(cid:2) (cid:2) (cid:3)(cid:2) (cid:1)(cid:2)(cid:3)(cid:2) (cid:1)(cid:2)(cid:3)(cid:2) (cid:1)(cid:2)(cid:3)(cid:2) (cid:4) (cid:4) (cid:4) (cid:5)(cid:6)(cid:7)(cid:8)(cid:7)(cid:9)(cid:10)(cid:11)(cid:12)(cid:9)(cid:13)(cid:14)(cid:6)(cid:7) (cid:15)(cid:16)(cid:9)(cid:14)(cid:17)(cid:16)(cid:14)(cid:9)(cid:18)(cid:10)(cid:19)(cid:8)(cid:10)(cid:20) (cid:22)(cid:19)(cid:15)(cid:17)(cid:23)(cid:18)(cid:9)(cid:10)(cid:5)(cid:9)(cid:12)(cid:24)(cid:18)(cid:17)(cid:16)(cid:19)(cid:12)(cid:8) (cid:21)(cid:19)(cid:13)(cid:18)(cid:8)(cid:15)(cid:19)(cid:12)(cid:8)(cid:15) (cid:1)(cid:2)(cid:3)(cid:4)(cid:5)(cid:2)(cid:6)(cid:7)(cid:8)(cid:9)(cid:10)(cid:11)(cid:12)(cid:7)(cid:13)(cid:10)(cid:14)(cid:8)(cid:13)(cid:10)(cid:15)(cid:3)(cid:16)(cid:17)(cid:18)(cid:2)(cid:13)(cid:19)(cid:14)(cid:8)(cid:13)(cid:11)(cid:20)(cid:21)(cid:8)(cid:22)(cid:11)(cid:20)(cid:22)(cid:12)(cid:23)(cid:12)(cid:7)(cid:1) (cid:2) (cid:1)(cid:3)(cid:3)(cid:2) (cid:1) (cid:2) (cid:1)(cid:2)(cid:20) (cid:1)(cid:3)(cid:3)(cid:2) (cid:1)(cid:2)(cid:20) (cid:25)(cid:2)(cid:4) (cid:25)(cid:2) (cid:4) (cid:1)(cid:2)(cid:12)(cid:7)(cid:12)(cid:23)(cid:19)(cid:23)(cid:10)(cid:15)(cid:3)(cid:24)(cid:15)(cid:19)(cid:25)(cid:15)(cid:26)(cid:27)(cid:16)(cid:15)(cid:19)(cid:23)(cid:15)(cid:28)(cid:14)(cid:10)(cid:15)(cid:26)(cid:29)(cid:24)(cid:30)(cid:15)(cid:11)(cid:31)(cid:7)(cid:10)(cid:5) (cid:15)!(cid:14)(cid:10)(cid:15)"(cid:20)(cid:7)(cid:10)(cid:9)(cid:31)(cid:7)(cid:10)(cid:15)(cid:19)(cid:25)(cid:15)#(cid:19)(cid:10)$(cid:10)(cid:13)(cid:15)$(cid:19)(cid:28)(cid:14)(cid:15)(cid:27)(cid:15)(cid:20)(cid:23)(cid:15)(cid:28)(cid:20)(cid:22) (cid:26) (cid:26) (cid:1) (cid:1) (cid:20) (cid:4) (cid:4) (cid:20) (cid:27)(cid:28)(cid:17)(cid:12)(cid:8)(cid:11)(cid:19)(cid:29)(cid:14)(cid:9)(cid:7)(cid:16)(cid:19)(cid:12)(cid:8) (cid:30)(cid:28)(cid:17)(cid:12)(cid:8)(cid:11)(cid:19)(cid:29)(cid:14)(cid:9)(cid:7)(cid:16)(cid:19)(cid:12)(cid:8) (cid:24)%&(cid:15)(cid:25)(cid:8)(cid:25)(cid:28)(cid:10)" (cid:15)!(cid:14)(cid:10)(cid:15)(cid:7)(cid:20)$(cid:10)(cid:25)(cid:28)(cid:15)(cid:22)(cid:11)(cid:19)(cid:20)(cid:11)(cid:19)(cid:28)(cid:8)(cid:15)(cid:6)(cid:11)(cid:20)(cid:31)(cid:22)(cid:15)(cid:19)(cid:25)(cid:15)’(cid:10)(cid:14)(cid:19)(cid:23)(cid:13)(cid:15)(cid:28)(cid:14)(cid:10)(cid:15)(cid:9)(cid:14)(cid:19)(cid:11)(cid:12)(cid:7)(cid:15)(cid:9)(cid:12)(cid:11)’(cid:20)(cid:23)(cid:15)(cid:12)(cid:28)(cid:20)" Absolute configuration. COOCH3, CONH2, COCH3, CHO, CH2OH, without reference to a tuned musical instru- C6H5, C2H5, CH3, H, with hydrogen lowest. ment. The molecule is viewed with the group of absolute space Space that exists as a lowest priority behind the chiral atom. If the background to events and processes and is clockwise arrangement of the other three not affected by objects or other entities in groups is in descending priority, the com- the universe. The idea underpins Newtonian pound belongs to the R-series; if the de- physics, although many physicists have al- scending order is anticlockwise it is in the ways regarded absolute space as an undesir- S-series. D-(+)-glyceraldehyde is R-(+)-glyc- able concept and suggested, as in *Mach’s Aeraldehyde. See illustration. principle, that fundamental physics should be described by *relational theories. • Information about IUPAC nomenclature for the absolute temperature See; R–S system . absolute expansivity See. absolute time Time that exists indepen- absolute humidity See. dently of any events or processes in the uni- verse. Like *absolute space, absolute time is absolute permittivity See. a basic concept in Newtonian physics. absolute pitch (perfect pitch) The ability absolute value (modulus) The square of a person to identify and reproduce a note root of the sum of the squares of the real absolute zero 4 a numbers in a *complex number, i.e. the ab- the total mass of the earth’s crust, often ex- solute value of the complex number z=x+ iy pressed as a percentage. For example, the is |z| = √(x2+y2). abundance of aluminium in the earth’s crust is about 8%. 2.The ratio of the number of absolute zero Zero of thermodynamic atoms of a particular isotope of an element *temperature (0 kelvin) and the lowest tem- to the total number of atoms of all the iso- perature theoretically attainable. It is the topes present, often expressed as a percent- temperature at which the kinetic energy of age. For example, the abundance of atoms and molecules is minimal. It is equiv- alent to –273.15°C or –459.67°F.See also uranium–235 in natural uranium is 0.71%. - ;. This is the natural abundance, i.e. the abun- dance as found in nature before any enrich- absorbed dose See. ment has taken place. absorptance Symbolα. The ratio of the abyssal zone The lower depths of the radiant or luminousÛux absorbed by a body ocean (below approximately 2000 metres), to theÛux falling on it. Formerly called ab- where there is effectively no light penetra- sorptivity, the absorptance of a *black body tion. Abyssal organisms are adapted for liv- is by deÜnition 1. ing under high pressures in cold dark absorption 1.(in chemistry) The take up conditions.See also  . of a gas by a solid or liquid, or the take up of a.c. See . a liquid by a solid. Absorption differs from *adsorption in that the absorbed substance acac The symbol for the *acetylacetonato permeates the bulk of the absorbing sub- ligand, used in formulae. stance. 2.(in physics) The conversion of the accelerant AÛammable material used to energy of electromagnetic radiation, sound, start and spread aÜre in cases of arson. streams of particles, etc., into other forms of Petrol and parafÜn are the substances com- energy on passing through a medium. A monly used. Traces of accelerant are de- beam of light, for instance, passing through a tectable by gas chromatography in forensic medium, may lose intensity because of two work. effects: scattering of light out of the beam, and absorption of photons by atoms or mol- acceleration Symbola. The rate of in- ecules in the medium. When a photon is ab- crease of speed or velocity. It is measured in sorbed, there is a transition to an excited ms–2. For a body moving linearly with con- state. 3.(in biology) The movement ofÛuid stant acceleration afrom a speed uto a or a dissolved substance across a plasma speedv, membrane. In many animals, for example, a=(v–u)/t=(v2–u2)/2s soluble food material is absorbed into cells wheretis the time taken and sthe distance lining the alimentary canal and thence into covered. the blood. In plants, water and mineral salts If the acceleration is not constant it is are absorbed from the soil by the *roots. See given by dv/dt= d2s/dt2. If the motion is not ; . linear the vector character of displacement, absorption coefÜcient 1.(in physics) velocity, and acceleration must be consid- SeeL’ . 2.(in chemistry) The ered.See also  . volume of a given gas, measured at standard acceleration of free fall Symbolg. The temperature and pressure, that will dissolve acceleration experienced by any massive ob- in unit volume of a given liquid. ject falling freely in the earth’s gravitational absorption indicator See - Üeld. Experimentally this is almost constant . for all positions near the earth’s surface, in- absorption spectrum See. dependent of the nature of the falling body (provided air resistance is eliminated). This absorptivity See. is taken to indicate the strict proportionality of *weight (the force causing the accelera- ABS plastic Any of a class of plastics based tion) and inertial *mass, on the basis of on acrylonitrile–butadiene–styrene copoly- Newton’s second law of motion (see mers. N’   ). There is some abundance 1.The ratio of the total mass variation of gwith latitude, because of the of a speciÜed element in the earth’s crust to earth’s rotation and because the earth is