A dictionary of science. 5th ed

893 Pages·2005·7.47 MB·english

by  Daintith

A Dictionary of
Science
FIFTH EDITION
3
1
Great Clarendon Street, Oxford ox2 6dp
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First edition, under the title Concise Science Dictionary, 1984
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Third edition 1996
Fourth edition 1999 retitled A Dictionary of Science
Fifth edition 2005
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ISBN 0–19–280641–6 978–0–19–280641–3
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Preface
This fifth 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 fifth edition over 300 new entries have been added to the text,
incorporating recent advances in all the major fields and increased coverage of
climatology, seismology, 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
2005
Contents
Preface vii
Credits viii
Dictionary 1
Atomic Theory Chronology 63
The Big-Bang Theory (Feature) 88
Biochemistry Chronology 92
Cell Biology Chronology 144
Cosmology Chronology 201
Crystal Defects (Feature) 212
Electronics Chronology 277
El Niño (Feature) 286
Explosives Chronology 309
Genetically Modified Organisms (Feature) 352
Learning in Animals (Feature) 470
Microscopy Chronology 527
Moon Exploration Chronology 540
Magnetic Resonance Imaging (Feature) 568
Plastics Chronology 637
Polymers (Feature) 648
Refrigeration (Feature) 700
Solar System (Feature) 762
Optical Astronomical Telescopes (Feature) 805
Vitamins Chronology 857
Appendices 881
SI units 881
Fundamental constants 883
The solar system 883
Geological time scale 884
Simplified classification of the plant kingdom 885
Simplified classification of the animal kingdom 886
The periodic table 887
Useful websites 888
A
aa See lava. position of a star as a result of the earth’s
AAS See atomic absorption spec- motion round the sun. Light appears to
troscopy. come from a point that is slightly dis-
placed in the direction of the earth’s mo-
ab- A preÜx attached to the name of a tion. The angular displacement α= v/c,
practical electrical unit to provide a name where v is the earth’s orbital velocity and
for a unit in the electromagnetic system c is the speed of light.
of units (see electromagnetic units), e.g.
abampere, abcoulomb, abvolt. The preÜx abiogenesis The origin of living from
nonliving matter, as by *biopoiesis. See
is an abbreviation of the word ‘absolute’ also spontaneous generation.
as this system is also known as the abso-
lute system. Compare stat-. In modern abiotic factor Any of the nonliving fac-
practice both absolute and electrostatic tors that make up the abiotic environ-
units have been replaced by *SI units. mentin which living organisms occur.
They include all the aspects of climate,
abdomen The posterior region of the
geology, and atmosphere that may affect
body trunk of animals. In vertebrates it the biotic environment. Compare biotic
contains the stomach and intestines and factor.
the organs of excretion and reproduction.
It is particularly well deÜned in mam- abomasum The fourth andÜnal cham-
mals, being separated from the *thorax ber of the stomach of ruminants. It leads
by the *diaphragm. In many arthropods, from the *omasum and empties into the
such as insects and spiders, it may be seg- small intestine. The abomasum is re-
mented. ferred to as the ‘true stomach’ as it is in
Abelian group See group. this chamber that protein digestion oc-
curs, in acidic conditions. See
aberration 1.(in optics) A defect in the ruminantia.
image formed by a lens or curved mirror.
ABO system One of the most impor-
In chromatic aberration the image formed
tant human *blood group systems. The
by a lens (but not a mirror) has coloured
system is based on the presence or ab-
fringes as a result of the different extent
sence of *antigens A and B on the surface
to which light of different colours is re-
of red blood cells and of *antibodies
fracted by glass. It is corrected by using
against these in blood serum. A person
an *achromatic lens. In spherical aberra-
whose blood contains either or both
tion, the rays from the object come to a
these antibodies cannot receive a transfu-
focus in slightly different positions as a
sion of blood containing the correspond-
result of the curvature of the lens or mir-
ing antigens as this would cause the red
ror. For a mirror receiving light strictly cells to clump (see agglutination). The
parallel with its axis, this can be cor-
table illustrates the basis of the system:
rected by using a parabolic surface rather
people of blood group O are described as
than a spherical surface. Spherical aberra-
‘universal donors’ as they can give blood
tion in lenses is minimized by making
to those of any of the other groups. See
both surfaces contribute equally to the also immune response.
ray deviations, and can (though with re-
duced image brightness) be reduced by abscisic acid A naturally occurring
the use of diaphragms to let light pass plant *growth substance that appears to
only through the centre part of the lens. be involved primarily in seed maturation,
See also astigmatism; coma. 2.(in astron- stress responses (e.g. to heat and water-
omy) The apparent displacement in the logging), and in regulating closure of leaf
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
The ABO blood group system
pores (stomata). In seeds, it promotes the lates the structure of the molecule to
synthesis of storage protein and prevents some reference molecule. In the case of
premature germination. In leaves, abscisic sugars and similar compounds, the
acid is produced in large amounts when dextrorotatory form of glyceraldehyde
the plant lacks sufÜcient water, promot- (HOCHCH(OH)CHO), 2,3-dihydroxy-
2
ing closure of stomata and hence reduc- propanal) was used. The rule is as fol-
ing further water losses. It was formerly lows. Write the structure of this molecule
believed to play a role in *abscission, down with the asymmetric carbon in the
hence the name. centre, the –CHO group at the top, the
abscissa See cartesian coordinates. –OH on the right, the –CH2OH at the bot-
tom, and the –H on the left. Now imagine
abscission The separation of a leaf, that the central carbon atom is at the cen-
fruit, or other part from the body of a tre of a tetrahedron with the four groups
plant. It involves the formation of an ab- at the corners and that the –H and –OH
scission zone, at the base of the part, come out of the paper and the –CHO and
within which a layer of cells (abscission –CHOH groups go into the paper. The re-
2
layer) breaks down. This process is sup- sulting three-dimensional structure was
pressed so long as sufÜcient amounts of taken to be that of d-glyceraldehyde and
*auxin, a plant growth substance,Ûow called d-glyceraldehyde. Any compound
from the part through the abscission that contains an asymmetric carbon atom
zone. However, if the auxinÛow declines, having this conÜguration belongs to the
for example due to injury or ageing, ab- d-series. One having the opposite conÜgu-
scission is activated and the part becomes ration belongs to the l-series. It is impor-
separated. tant to note that the preÜxes d- and l- do
absolute 1.Not dependent on or rela- not stand for dextrorotatory and laevoro-
tive to anything else, e.g. *absolute zero. tatory (they are not the same as d- and l-).
2.Denoting a temperature measured on In fact the arbitrary conÜguration as-
an absolute scale, a scale of temperature signed to d-glyceraldehyde is now known
based on absolute zero. The usual abso- to be the correct one for the dextrorota-
lute scale now is that of thermodynamic tory form, although this was not known
*temperature; its unit, the kelvin, was for- at the time. However, all d-compounds
merly called the degree absolute (°A) and are not dextrorotatory. For instance, the
is the same size as the degree Celsius. In acid obtained by oxidizing the –CHO
British engineering practice an absolute group of glyceraldehyde is glyceric acid
scale with Fahrenheit-size degrees has (1,2-dihydroxypropanoic acid). By conven-
been used: this is the Rankine scale. tion, this belongs to the d-series, but it is
in fact laevorotatory; i.e. its name can be
absolute alcohol See ethanol. written as d-glyceric acid or l-glyceric acid.
absolute conÜguration A way of de- To avoid confusion it is better to use + (for
noting the absolute structure of an optical dextrorotatory) and – (for laevorotatory),
isomer (see optical activity). Two conven- as in d-(+)-glyceraldehyde and d-(–)-
tions are in use: The d–l convention re- glyceric acid.
3 absolute value
CHO CHO CHO a
H C OH C HCOH
H OH
CHOH CHOH CHOH
2 2 2
planar formula structure in 3 Fischer projection
dimensions
D–Lconvention: D-(+)-glyceraldehyde (2,3-dihydroxypropanal)
H COOH
C H
CH3 COOH CH3 NH2
NH
2
D–Lconvention: D-alanine (R is CH2in the CORN rule); the molecule is viewed with H on top
1 1
C C
3 2 2 3
R–configuration S–configuration
R–S system: the lowest priority group is behind the chiral carbon atom
The d–l convention can also be used to the r-series; if the descending order is
with alpha amino acids (compounds with anticlockwise it is in the s-series. d-(+)-
the –NH group on the same carbon as the glyceraldehyde is r-(+)-glyceraldehyde. See
2
–COOH group). In this case the molecule illustration.
is imagined as being viewed along the absolute expansivity See expansivity.
H–C bond between the hydrogen and the
asymmetric carbon atom. If the clockwise absolute humidity See humidity.
order of the other three groups is –COOH, absolute permittivity See permittiv-
s–eRr, i–eNs;H o2t,h tehrew aisme iint ob aecloidn gbse ltoon tghse t lo- stehreie ds.- ity.
This is known as the CORN rule. absolute pitch (perfect pitch) The abil-
The r–s convention is a convention ity of a person to identify and reproduce a
based on priority of groups attached to note without reference to a tuned musical
the chiral carbon atom. The order of pri- instrument.
ority is I, Br, Cl, SO3H, OCOCH3, OCH3, absolute temperature See absolute;
OH, NO2, NH2, COOCH3, CONH2, COCH3, temperature.
CHO, CHOH, CH, CH, CH, H, with hy-
2 6 5 2 5 3
drogen lowest. The molecule is viewed absolute value (modulus) The square
with the group of lowest priority behind root of the sum of the squares of the real
the chiral atom. If the clockwise arrange- numbers in a *complex number, i.e. the
ment of the other three groups is in de- absolute value of the complex number
scending priority, the compound belongs z = x + iy is |z| = √(x2+ y2).
absolute zero 4
a absolute zero Zero of thermodynamic mass of a speciÜed element in the earth’s
*temperature (0 kelvin) and the lowest crust to the total mass of the earth’s crust,
temperature theoretically attainable. It is often expressed as a percentage. For ex-
the temperature at which the kinetic en- ample, the abundance of aluminium in
ergy of atoms and molecules is minimal. the earth’s crust is about 8%. 2.The ratio
It is equivalent to –273.15°C or –459.67°F. of the number of atoms of a particular iso-
See also zero-point energy; cryogenics. tope of an element to the total number of
absorbed dose See dose. atoms of all the isotopes present, often ex-
pressed as a percentage. For example, the
absorptance Symbol α. The ratio of the abundance of uranium–235 in natural ura-
radiant or luminousÛux absorbed by a nium is 0.71%. This is the natural abun-
body to theÛux falling on it. Formerly dance, i.e. the abundance as found in
called absorptivity, the absorptance of a nature before any enrichment has taken
*black body is by deÜnition 1. place.
absorption 1.(in chemistry) The take abyssal zone The lower depths of the
up of a gas by a solid or liquid, or the take ocean (below approximately 2000 metres),
up of a liquid by a solid. Absorption dif- where there is effectively no light pene-
fers from *adsorption in that the ab- tration. Abyssal organisms are adapted for
sorbed substance permeates the bulk of living under high pressures in cold dark
the absorbing substance. 2.(in physics) conditions. See also aphotic zone.
The conversion of the energy of electro-
magnetic radiation, sound, streams of par- a.c. See alternating current.
ticles, etc., into other forms of energy on acceleration Symbol a. The rate of in-
passing through a medium. A beam of crease of speed or velocity. It is measured
light, for instance, passing through a in ms–2. For a body moving linearly with
medium, may lose intensity because of constant acceleration a from a speed u to
two effects: *scattering of light out of the a speed v,
beam, and absorption of photons by
atoms or molecules in the medium. When a=(v–u)/t=(v2–u2)/2s
a photon is absorbed, there is a transition where t is the time taken and s the dis-
to an excited state. 3.(in biology) The tance covered.
movement ofÛuid or a dissolved sub- If the acceleration is not constant it is
stance across a plasma membrane. In given by dv/dt = d2s/dt2. If the motion is
many animals, for example, soluble food not linear the vector character of displace-
material is absorbed into cells lining the ment, velocity, and acceleration must be
alimentary canal and thence into the considered. See also rotational motion.
blood. In plants, water and mineral salts
are absorbed from the soil by the *roots. acceleration of free fall Symbol g.
See osmosis; transport protein. The acceleration experienced by any mas-
sive object falling freely in the earth’s
absorption coefÜcient 1.(in physics) gravitationalÜeld. Experimentally this is
See lambert’s laws. 2.(in chemistry) The almost constant for all positions near the
volume of a given gas, measured at stan- earth’s surface, independent of the nature
dard temperature and pressure, that will of the falling body (provided air resistance
dissolve in unit volume of a given liquid. is eliminated). This is taken to indicate
absorption indicator See adsorption the strict proportionality of *weight (the
indicator. force causing the acceleration) and *iner-
tial mass, on the basis of *Newton’s sec-
absorption spectrum See spectrum.
ond law of motion. There is some
absorptivity See absorptance. variation of g with latitude, because of the
earth’s rotation and because the earth is
ABS plastic Any of a class of plastics
not completely spherical. The standard
based on acrylonitrile–butadiene–styrene value is taken as 9.80665ms–2. The accel-
copolymers.
eration of free fall is also called the accel-
abundance 1.The ratio of the total eration due to gravity.
5 acetals
accelerator 1.(in physics) An apparatus retina. In humans and some other mam- a
for increasing the kinetic energies of mals accommodation is achieved by reÛex
charged particles, used for research in nu- adjustments in the shape of the lens
clear and particle physics. See cyclotron; brought about by relaxation and contrac-
linear accelerator; synchrocyclotron; tion of muscles within the *ciliary body.
synchrotron. 2.(in chemistry) A sub- 2.(in animal behaviour) Adjustments
stance that increases the rate of a chemi- made by an animal’s nervous or sensory
cal reaction, i.e. a catalyst. systems in response to continuously
changing environmental conditions.
acceptor 1.(in chemistry and biochem-
istry) A compound, molecule, ion, etc., to accretion The way in which collisions
which electrons are donated in the forma- with relatively slow-moving smaller ob-
tion of a coordinate bond. 2.(in biochem- jects add to the mass of a larger celestial
istry) A *receptor that binds a hormone object. The process accelerates as the in-
without any apparent biological response. creased mass strengthens the gravita-
3.(in physics) A substance that is added as tionalÜeld of the larger object. For
an impurity to a *semiconductor because example, the planets are thought to have
of its ability to accept electrons from the formed by the accretion of dust particles
valence bands, causing p-type conduction onto *planetesimals. Other accreting ob-
by the mobile positive holes left. Compare jects probably include black holes and
donor. protostars.
acceptor levels Energy levels of an ac- accretion disc A disc-shaped rotating
ceptor atom in a *semiconductor, such as mass formed by gravitational attraction.
aluminium, in silicon. These energy levels See black hole; neutron star; white
are very near the top of the valence band, dwarf.
and therefore cause p-type conduction. See accumulator(secondary cell; storage
also energy band. battery)A type of *voltaic cell or battery
acclimation The physiological changes that can be recharged by passing a cur-
occurring in an organism in response to a rent through it from an external d.c. sup-
change in a particular environmental fac- ply. The charging current, which is passed
tor (e.g. temperature), especially under in the opposite direction to that in which
laboratory conditions. Thermal acclima- the cell supplies current, reverses the
tion studies reveal how such properties as chemical reactions in the cell. The com-
metabolic rate, muscle contractility, nerve mon types are the *lead–acid accumulator
conduction, and heart rate differ between and the *nickel–iron and nickel–cadmium
cold- and warm-acclimated members of accumulators. See also sodium–sulphur
the same species. These changes occur cell.
naturally during *acclimatization and acellular Describing tissues or organ-
equip the organism for living in, say, cold isms that are not made up of separate
or warm conditions. cells but often have more than one nu-
acclimatization 1.The progressive cleus (see syncytium). Examples of acellu-
adaptation of an organism to any change lar structures are muscleÜbres. Compare
in its natural environment that subjects it unicellular.
to physiological stress. 2.The overall sum acentric Describing an aberrant chro-
of processes by which an organism at- mosome fragment that lacks a cen-
tempts to compensate for conditions that tromere. Such fragments are normally
would substantially reduce the amount of lost because they are unable to orientate
oxygen delivered to its cells. Compare ac- properly during cell division.
climation.
acetaldehyde See ethanal.
accommodation 1.(in animal physiol-
acetaldol See aldol reaction.
ogy) Focusing: the process by which the
focal length of the *lens of the eye is acetals Organic compounds formed by
changed so that clear images of objects at addition of alcohol molecules to aldehyde
a range of distances are displayed on the molecules. If one molecule of aldehyde
acetamide 6
a (RCHO) reacts with one molecule of alco- cular contraction at *neuromuscular junc-
hol (R′OH) a hemiacetalis formed tions. Once acetylcholine has been re-
(RCH(OH)OR′). The rings of aldose sugars leased it has only a transitory effect
are hemiacetals. Further reaction with a because it is rapidly broken down by the
second alcohol molecule produces a full enzyme *cholinesterase.
acetal (RCH(OR′)). It is common to refer
2 acetylcholinesterase See
to both types of compounds simply as
cholinesterase.
‘acetals’. The formation of acetals is re-
versible; acetals can be hydrolysed back to acetyl coenzyme A (acetyl CoA) A
aldehydes in acidic solutions. In synthetic compound formed in the mitochondria
organic chemistry aldehyde groups are when an acetyl group (CHCO–), derived
3
often converted into acetal groups to pro- from the breakdown of fats, proteins, or
tect them before performing other reac- carbohydrates (via *glycolysis), combines
tions on different groups in the molecule. with the thiol group (–SH) of *coenzyme
See also ketals. A. Acetyl CoA feeds into the energy gener-
R_C___O + R′OH R__C__OR′ athtien sgy *nKthreebsiss cayncdle o axnidda atlisoon polfa yfast aty r oacleid isn.
H H OH acetylene See ethyne.
aldehyde alcohol hemiacetal
acetylenes See alkynes.
RH__C__OORH′ + R′OH HR__C__OORR′′+ H2O aacceettyyll igdreouSepe c Saere beitdhea.noyl group.
Formation of acetals achene A dry indehiscent fruit formed
from a single carpel and containing a sin-
gle seed. An example is the feathery
acetamide See ethanamide.
achene of clematis. Variants of the
acetanilide A white crystalline primary achene include the *caryopsis, *cypsela,
amide of ethanoic acid, CHCONHCH; *nut, and *samara. See also etaerio.
3 6 5
r.d. 1.2; m.p. 114.3°C; b.p. 304°C. It is
Acheson process An industrial process
made by reacting phenylamine (aniline)
for the manufacture of graphite by heat-
with excess ethanoic acid or ethanoic an-
ing coke mixed with clay. The reaction in-
hydride and is used in the manufacture of
volves the production of silicon carbide,
dyestuffs and rubber. The full systematic which loses silicon at 4150°C to leave
name is N-phenylethanamide.
graphite. The process was patented in
acetate See ethanoate. 1896 by the US inventor Edward Goodrich
acetate process See rayon. Acheson (1856–1931).
acetic acid See ethanoic acid. achondrite A stony meteorite that has
no spherical silicate particles (chondrules)
acetoacetic acid See 3-oxobutanoic found in the meteorites called chondrites.
acid. Achondrites do not contain iron or nickel
acetoacetic ester See ethyl 3-oxo- and have a coarser crystal structure than
butanoate. chondrites.
acetone See propanone; ketone body. achromatic lens A lens that corrects
for chromatic *aberration by using a com-
acetylation See acylation. bination of two lenses, made of different
acetyl chloride See ethanoyl kinds of glass, such that their *dispersions
chloride. neutralize each other although their *re-
fractions do not. The aberration can be re-
acetylcholine(ACh) One of the main
duced further by using an apochromatic
*neurotransmitters of the vertebrate
lens, which consists of three or more dif-
nervous system. It is released at some
ferent kinds of glass.
(cholinergic) nerve endings and may be
excitatory or inhibitory; it initiates mus- acid 1.A type of compound that con-