N

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P

Parts Per Million (ppm) and Parts Per Billion (ppb) : These terms give scientists a way to describe how much of a substance is contained in a sample: parts of analyte per million parts of sample, for instance. In atmospheric chemistry these become volume parts of analyte per volume parts of atmosphere: ppmv, ppbv, etc. At low analyte gas phase concentrations the analyte is assumed to act as an ideal gas. For instance, a 1 ppmv concentration of formaldehyde would represent 1 liter of formaldehyde per every 1,000,000 liters of air; also equivalent to 1 microliter of H₂CO per 1 L air. In gas phase concentrations these units are also called gas phase mixing ratios. The reason is because they are just that, ratios of analyte volume to sample volume; the volume of the sample doesn't matter.
pascal (Pa) : Unit of pressure equivalent to one Newton per square metre.
pathology : The branch of medicine concerned with the study of disease and disease processes in order to understand their causes and nature. The speciality originated in the mid 19th century when Virchow demonstrated that changes in the structure of cells and tissues were related to specific diseases.
Pauli exclusion principle : In any atomic system no two electrons can have identical wave functions.
PCV Systems : A PCV system is an air pollution control device in automobile engines. PCV stands for positive crankcase ventilation. Automobile makers began installing PCV systems in all new cars in 1963. It helps to recycle hydrocarbon contaminated gases inside the engine (blowby) back into the engine's combustion process.
"pecking order" : The establishment of social hierarchies, first noted in domestic chickens.
pedicel : A flower stalk supporting several flowers without footstalks.
Pedosphere : This is the area of the Earth comprised of the solid plates of the continental crust, loose rocks and soil.
penumbra : A partly shaded region round the shadow of an opaque body.
peptide bond : The bond, formed by dehydration synthesis (elimination of water), which links together two amino acids.
perennial : Rootstocks that increase and expand yearly.
perianths : Flowers showing no distinction between calyx and corolla.
Percutaneous Absorption : Absorption via the skin, e.g. due to local contamination or a splash of chemical.
Perihelion Date (T) : The date an object reaches its closest distance from the sun.
Perihelion Distance (q) : The point in an orbit when an object is closest to the sun. The value is usually given in astronomical units.
Period (astronomical): The amount of time, usually given in years, that it takes an object to orbit the sun.
periodic table : A tabular arrangement of the elements in order of the atomic numbers, which also brings together those elements who's atoms have a similar pattern of orbiting electrons. Chemically related elements consequently tend to appear in the same column or row of the table. Go to table.
perithecium : bottle-shaped ascocarp with a pore at the top through which individual asci are discharged.
Permafrost : Soil, silt and rock located in perpetually cold areas which remains frozen year-round. Though a thin layer may thaw during summer months, the majority of the permafrost in a given location will remain frozen until the local climate dramatically changes, as from continental drift toward the equator or global warming.
permeability : The ability of a material to permit a substance to pass through it. From an actual quantitative level, it is the amount of a substance which passes through the material under given conditions.
Permian period : The last geological period of the Palaeozoic era, occurring about 3.7 to 2.8 x 10⁸ years ago. Widespread continental conditions prevailed, which continued into the Triassic, and the two periods are often linked together as the Permo-Triassic, during which the New Red Sandstone was laid down.
Permit-To-Work : A document needed when safeguards provided in normal production are unavailable and the manner in which a job is done is critical to safety. Identifies conditions required for safe operation.
peroxisome : A cytoplasmic cell organelle containing enzymes for the production and decomposition of hydrogen peroxide.
Peroxyacetylnitrate (PANs) : A class of chemical substances found as a pollutant in the troposphere, formed by photolysis from natural and manufactured organic chemicals. These chemicals act as irritants and mutagens in mammals and are toxic to many plants.
persistent train : train luminosity that lasts more than a second.
perturbation : a disturbance; often develops into a low pressure system.
peta (P) : 10¹⁵
pH : Symbol for the logarithmic scale, running from 0 to 14, representing the concentration of hydrogen ions or protons (usually hydronium ions) per litre solution. On the pH scale 7 represents neutrality, the lower numbers acidity (acids) and the higher numbers alkalinity (bases).
pH : The negative logarithm of the hydrogen ion concentration of a solution. It is the quantitative expression of the acidity and alkalinity of a solution and has a scale that ranges from about 0 to 14. pH 7 is neutral; <7 is acidic; and >7 is alkaline.
phagocyte : A cell in the body capable of engulfing cytoplasm for enzymatic breakdown (phagocytosis). Phagocytes are found in large numbers lining the walls of lymph node sinuses; they destroy bacteria that have entered the body and been picked up by the lymphatic system. Leucocytes and macrophages are examples of phagocytes in man.
phagocytosis : The engulfing of micro-organisms, other cells, or foreign particles by a cell. For example, phagocytosis occurs when an amoeba engulfs its prey or when a white blood cell engulfs a bacterium.
pharmacology : The study of the action of drugs on living organisms. Pharmacologists examine the uptake of drugs after administration, the routes by which they reach their site of actin, their subsequent effects, how drugs are destroyed by the body, their unwanted side effects, and the interaction between different drugs. Clinical pharmacology (therapeutics) studies the effects of drugs in treating disease.
Phenol :
1) A corrosive poisonous crystalline acidic compound present in coal tar and wood tar that in dilute solutions is used as a disinfectant and
2) any of various acidic compounds analogous to phenols and regarded as hydroxyl derivatives of aromatic hydrocarbons. When coal and wood are burned for energy, phenols are released into the atmosphere.
phenotype (genetics): The outward appearance of an organism, as contrasted with its genetic make up (genotype).
Phi ( F, f ) :
Protoplasm : The name given to the material of a biological cell.
phlogiston theory : The theory that held that the substance phlogiston was contained in all combustible bodies and was released from these bodies upon their burning (producing phlogisticated air). It remained popular until the advent of the oxygen theory of combustion.
phon : A unit used for measuring the loudness of sound equal to the intensity in decibels of a sound of a frequency 1000 hertz which appears to the ear to be as loud as the sound to be measured.
phosphoglyceric acid (PGA) : An intermediate product in carbohydrate metabolism, composed of a 3-carbon backbone with a phosphate group attached to one (usually position 3) of the carbons.
phospholipids : An important structural part of the cellular membrane, containing phosphorus, fatty acids, glycerine, and nitrogenous base.
phosphorylation : The addition of a phosphate group ( such as H₂PO₃) to a compound, as in oxidative of ADP (producing ATP) during respiration.
Photic Zone : In the ocean (or in lakes) this is the area near the surface with enough light to support photosynthesis. In this zone, both the chemical and biological activity can be enhanced by penetrating solar radiation. This zone is about 20 meters in depth in the ocean. In the upper surface of this zone, the marine photochemistry is most vigorous. Changes in the ultraviolet light content penetrating this region because of changes in the UV-blocking ability of the ozone layer may create unexpected biological results there.
Photochemical Smog : Natural and artificially emitted hydrocarbons in the presence of oxides of nitrogen undergo photochemical reactions which produce a cloud of toxic chemicals including ozone and a variety of caustic agents. This process is powered by sunlight and some of the products, such as ozone, reach a peak soon after photon flux from the sun reaches a maximum, around midday. The thermal inversions often associated with some cities can lead to a dangerous buildup of smog in urban areas. Human deaths have been attributed to photochemical smog since the Industrial Revolution in cities such as London and New York.
photoconductivity : The increase in the conductivity of certain semi-conductors, such as selenium, when exposed to light. It occurs when photons excite electrons in the material form the valence band into the conduction band.
Photodissociation : This is a specific type of photolysis reaction, in which the destruction of a molecule is initiated strictly by solar energy.
photoelectric effects : A number of effects in which electromagnetic radiation interacts with matter, frequently with the emission of electrons. These effects include photo conductivity, he photovoltaic effect ad the Compton effect and the Augur effect. The frequency of the radiation (f) has to be such that the energy of the photon , hf (where h is Planck's constant) is sufficient to liberate the electron.
For solids the minimum energy required is called the work function: for free atoms or molecules it is equal to the first ionisation potential, the effect then being known as photoionization. For most substances, an ultraviolet frequency is needed to eject an electron, but for some metals, such as caesium, visible light is sufficient.
photoionization : The ionization of an atom when it is bombarded with electromagnetic radiation. The frequency of the radiation has to be such that the energy of its photons exceeds the first ionization potential of the atom.
Photolysis : The destruction of a molecule by electromagnetic radiation, which provides the energy required for a constituent atom to break the chemical bonds between it and the other atoms comprising the molecule.
photon : The quantum of electromagnetic radiation, having an energy of hf where h is Planck's constant and f is the frequency of the radiation. It may be regarded as an elementary particle with spin 1 and zero mass that travels at the speed, of light.
Photostationary State : This describes a condition in which there is equilibrium in a photochemical reaction. For this condition to take place the rate of dissociation of the reactants has to be equal to the rate of their recombination.
Photosynthesis : a biological process which plays a vital role in cycling the atmosphere's carbon dioxide, while simultaneously producing oxygen and other complex substances. Green plants, with chlorophyll, utilize the sun's energy to convert carbon dioxide and water into the plant biomass while oxygen that is released into the atmosphere.
photovoltaic effect : The production of a voltage when light falls on certain materials coated with another substance. The effect can be detected by connecting the two materials through an external circuit to generate a current. It occurs in copper (I) oxide on copper and in selenium on iron.
phrenology : phyletic speciation : The process of evolutionary change in which one population gives rise, over time, to another single population genetically different from the original.
phylogenetic chart : A diagram showing the evolutionary relationships among a group of species, or with a single species. The so called family tree is an example of a phylogenetic chart.
phylogeny : The study of the evolutionary history of a species.
physical environment : All of the elements surrounding an organism but excluding other living organisms.
physostigmine (ersine) : Extracted by some tribes from the calabar bean and used in ceremonies as an "ordeal" poison. The effects of ingestion are mental excitement and hallucination; an overdose of the drug causes vomiting, epigastric pains, and in severe cases interferes with the function of the heart causing death.
physiology : phytol : The alcohol constituent of chlorophyll.
Pi ( P, p ) : In mathematics the value (approx. 3.142 or 22/7 ) that is equivalent to the circumference of a circle divided by it's diameter.
pico (p) : 10^-12
pilo carpine : an alkaloid extracted from the dried leaves of the jaborandi and used medicinally in eyedrops to constrict the pupil and treat glaucoma.
Pinhole Camera :

Q

R

r- strategists :
raceme : Flowers arranged like a spike, but with footstalks.
rad : The unit of absorbed dose on ionising radiation equivalent to an energy absorption of 100 ergs per gram of irradiated material.
radial velocity : The velocity of a star etc. along the line of sight, i.e. towards or away from the earth. It is calculated from the Doppler shift on the lines of the stars spectrum.
radian : The SI unit of plane angle equal to the angle subtended at the centre of a circle by an arc equal in length to the radius of the circle, i.e. 1 rad = q(p/180).
Radiant : The point from which a meteor appears to emanate.
Radiant Drift : The movement of a meteor shower's radiant against the star background. This characteristic is common to all meteor showers and is caused by Earth's passage through a meteor stream.
Radiation Flux : This is defined as the way heat from the sun is absorbed, scattered, returned, or deposited around the earth and can be expressed as some radiation arrival rate per the unit of area of the surface. The radiation flux can be the total amount of radiation that the earth collects, emits, and disperses.
Radiative Forcing : Reduction of radiation reflecting from earth per units of increase of a chemical component that causes this change in the atmosphere. The result is often used to compare the relative effect of greenhouse gases which can alter climate on earth. This means that components that are present in the atmosphere at low concentrations (e.g. methane at 1.7 ppmv) but with high radiative forcing have a greater effect on global warming than higher concentration components with a lower radiative forcing.
Radical (free radical) : A highly reactive molecule or atom with an unpaired electron. The species is often represented by a formula with a single dot as the unpaired electron.
Radical Chain Reaction : Free radicals are molecules that, through photolysis or chemical reaction, have an unpaired electron in their outer valance shell. These radicals are very reactive and thus have a short life. When a free radical reacts with a more stable molecule, the radical often pulls an atom from it and becomes a stable molecule itself. The original molecule then becomes a free radical and will react with other species of atoms and molecules in a long series (or chain) of reactions until the process reaches the termination phase. In this phase two free radicals combine, sharing the pair of electrons and breaking the chain.
Radical Propagation : Free radicals react with molecules, atoms, other radicals in long series of chain reactions. A radical is formed in the atmosphere through photolysis or chemical reaction. Radicals are very reactive and will pull atoms or electrons from other molecules to fill their outer valance shell. New radicals may formed from the original molecule which then react with another molecule, etc. This reaction propagates from one species to another until a termination reaction occurs. The termination reaction usually involves the reaction of two free radicals to form a stable product. Radioactive Decay - The spontaneous breakdown of certain kinds of atomic nuclei into one or more nuclei of different elements, involving the release of energy and subatomic particles.
radioactive decay : The decrease in mass of certain unstable elements by emission of elementary particles, continuing until a stable isotopic form has been reached.
Radiocarbon Dating : Establishing the relative age of various materials with the use of carbon -14. This involves measuring the amount of ¹⁴C and of ¹²C and comparing the measured ratio to the one established by the production of ¹⁴C in the upper atmosphere by cosmic rays. When an organism is alive the ¹⁴C : ¹²C ratio in its biomass is constant (because of constant atmospheric ¹⁴C production, difussion to the lower atmsophere, absorption by organisms, and because of constant ¹⁴C radioactive decay) but when the organism dies the ratio begins to change, at a very predictable rate. Therefore knowing the carbon -14 : carbon -12 ratio now in some artifact gives a very good measure of how long the carbon has been "dead." The object however must obviously have organic material either in it or on it for this method to work. Also the lenth of time one can "look back" is limited because the amount of carbon -14 must be detected with some certainty for the age to be known with confidence, and the longer the sample has been dead the less 14C is present because it is continually decaying.
radio galaxy : A radio source that lies beyond our Galaxy, is identified with an optical galaxy, and the radio-power output of which greatly exceeds that of a normal galaxy. The size can be immense. A massive black hole at the galaxy centre has been postulated as a possible energy source.
radiography : The technique of examining the internal structure by passing X-rays or gamma radiation through it to produce an image on a photographic plate or fluorescent screen. Radiography is used in medicine and in industry to find structural defects.
radiosonde : a light-weight instrument package carried aloft by a weather balloon; radios to earth upper atmosphere data.
Rainout : One item necessary for a rain drop to form is called a condensation nucleus. Pollutants in the air such as nitric acid and sulfuric acid form nucleation sites (particles) where water vapor often condenses and forms a droplet. As these droplets grow they collect more moisture and may ultimately fall out as precipitation. This accounts for some of the acid rain deposition on the planet's surface.
random errors : these result in repeat measurements on the same sample to vary in a number of tests.
rangefinder : a camera in which the subject is viewed through a separate view finder. There will always be the problem that what you see may not be what is taken, the classic examples being close ups of blurred fingers, and lens caps left on.
Raoult's law : The partial vapour pressure of any volatile component, A, of an ideal solution is equal to he vapour pressure of pure A multiplied by the mole fraction of A in the solution.
Rayleigh Scattering : The scattering of light by a body with a particle diameter (Dp) less than 0.03 micrometers is termed Rayleigh Scattering. The wavelength of light scattered is dependent on the Dp, and the amount of light scattered is dependent on the number of particles present per unit volume. Shorter visible wavelengths, such as blue, are scattered by smaller particles than are the longer wavelengths like red.
Reaction Rate : The speed of chemical reactions is expressed as a rate of change in the concentration of a participating species with respect to time.
Reasonably Practicable : The implication that the quantum of risk is balanced against the sacrifice or cost in terms of money, time and trouble necessary to avert that risk. If the risk overweighs the sacrifice or cost, additional precautions are necessary.
recessive (genetics) : referring to the relative lack of phenotypic effect of a gene in the presence of its dominant allele. Thus the gene for the blue eyes is said to be recessive for that for brown in the human population, because when one allele for blue eyes and one for brown eyes are present in an individual, the blue condition is masked and the individual has brown eyes. recombination (genetics), The formation of new genotypes (a combination of genes not present in either of the parents) in offspring due to independent assortment of genes and chromosomes during gamete formation.
red giant : A greatly distended cool but very luminous giant star, often variable in nature. It is one of the final evolutionary stages of a normal star, attained when its central hydrogen has been converted to helium. Hydrogen burning in a shell surrounding the inert helium core causes a rapid expansion and cooling of the outer atmosphere of the star.
red shift : An overall displacement towards larger wavelengths of the spectral lines of a celestial object. Its astronomical significance, suggested by Hubbell, is connected with it's use as the basis of the theory that the universe is expanding. A red shift usually arises from the Doppler effect, that is from recession of a celestial object. It increases as the objects radial velocity increases and for an extragalactic body can be used as a measure of distance. A gravitational redshift occurs whenever radiation is emitted by a body: it is generally negligible except when the gravitational field is very strong.
reduction (chemistry) : A reaction involving the gain of electrons.
reduction division : A cell division, during which the number of chromosomes in each daughter cell is reduced to one half of that found in the parent cell. This is accomplished by nuclear division without previous chromosomal division.
refraction : The bending of a beam of radiation as it passes from one medium to another. For a light ray the amount by which it is bent depends on the angle of the incident ray and on the refractive indices of the two media, the exact dependence being given by Snell's law. Refraction is caused by the difference in the velocity of the radiation of the two media. The ratio of the velocity of light in the media is known as the refractive index. If the first medium is a vacuum, the ratio is known as the absolute refractive index.
regeneration : The development process by which a lost part of an organism (such as an organ, part of an organ, or tissue) is replaced after damage. Repair of wounds and the regrowth of a salamanders amputated arm are examples of regeneration.
relative density (specific gravity): The density of a substance divided by the density of water at 4^oC. This value is numerically one thousandth of the density.
Relative Humidity : This is the ratio between the actual water vapor content of the atmosphere and the maximum water vapor content possible at that given temperature. If the temperature of a given parcel of air rises, the amount of moisture it can hold increases and as such its relative humidity decreases. If there is no change in temperature but the moisture content decreases then the relative humidity will again decrease because the ratio of actual water vapor present is less than the maximum amount the air could hold. Conversely, if the water content does not change but the temperature falls, the relative humidity increases until saturation and possible precipitation occurs.
relative humidity : a ratio of the amount of water vapour that the air is holding to the amount of water vapour the air can hold, which depends on temperature.
relative velocity : The velocity of one body relative to another.
Reportable Disease (UK) : A disease which must be reported to the authorities when linked to specified types of work. (The Reporting of Injuries Disease and Dangerous Occurrences Regulations 1985).
Respirable Dust : That fraction of total inhalable dust which penetrates to the gas exchange region of the lung.
respiratory assembly : A series of complex molecules (including cytochromes), found on the inner membranes of mitochondria, and capable of oxidation and reduction. Such assemblies accept electrons from reduced acceptors during the citric acid cycle and pass them along to the final acceptor, oxygen. The enzymes for oxidative phosphorylation are also components of the respiratory assembly.
Respiratory Sensitizer : A substance that may cause sensitization on inhalation, causing, e.g., asthma, rhinitis or extrinsic allergic alveolitis.
response : A change in behaviour on the part of an organism (or tissue) as a result of some chemical or physical change in the environment.
restriction fragment length polymorphism : a technique, also known as DNA fingerprinting, that allows familial relationships to be established by comparing the characteristic polymorphic patterns that are obtained when certain regions of genomic DNA are amplified (typically by PCR) and cut with certain restriction enzymes. In principle, an individual can be identified unambiguously by RFLP (hence the use of RFLP in forensic analysis of blood, hair or semen). Similarly, if a polymorphism can be identified close to the locus of a genetic defect, it provides a valuable marker for tracing the inheritance of the defect.
Return Stroke : A short-lived, high amplitude discharge of electricity that accompanies a cloud-to-ground lightning event. The bright lightning flash that is visible to the human eye is actually composed of extremely rapid electric discharges called strokes. The return stoke follows a downward extending leader, or conductive path of ionized air. The electrons in the cloud flow down this conductive pathway toward the surface of the earth. As electrons continually migrate down the path, electrons remaining higher up on the path in the cloud begin to consecutively move down the channel to the surface. Since the path of electron flow is progressively lengthened upward, the discharge of the elevated electrons high in the cloud to a lower place in the cloud and then down the pathway to the ground is called the return stroke.
reverse phase HPLC : chromatography in which the stationary phase is non-polar and the mobile phase is polar.
reversible reaction : A reaction system where reactants and products are inter convertible. If left to themselves , reversible chemical reactions reach an equilibrium point where just as much reactant is being converted into product as product into reactant at any time. Nearly all chemical reactions are to some extent reversible.
revolver : A short range small arm having a revolving cylinder containing the rounds behind the barrel. In single action types pressing the trigger cocks the weapon and simultaneously rotates the cylinder; further pressure fires it. Double action types perform these functions automatically but their stiffer mechanism impairs accuracy. Calibre's range from .21 inches to .455 inches.
Reynolds number :
Rhesus (Rh) factor : An antigen found in the red blood cells of certain human beings (designated Rh+). The Rh factor acts as an antigen so that individuals with this factor cannot donate blood to individuals who normally lack it (Rh- individuals). The factor derives its name as it was first discovered in the Rhesus monkey.
rho ( R, r ):
ribonuclectic acid (RNA) : A complex single stranded molecule consisting of repeating nucleotide bases; adenine, guanine, cytosine and uracil. At least three types of RNA are known, all of which are involved in transcribing the genetic code into protein.
ribosomal RNA (rRNA): A type of RNA found as part of the ribosomes. The function of rRNA is not well understood although it appears to have some role in protein synthesis.
ribosomes : Small particles found either free in the cytoplasm or attached to the outer surface of the endoplasmic reticulum in the cells of all eukaryotes and many prokaryotes. Ribosomes contain high concentrations of ribonucleic acid (RNA) and are centres of protein synthesis.
ricin poisoning :
Richter scale : A logarithmic scale (from 0-9) used to measure earthquake magnitude. It is based on seismic recordings and takes into account the distance from the epi-centre. The strongest earthquake so far recorded had a Richter scale value of 8.6
ridge : an area of high pressure. An area of anticyclonically curving winds.
rifle : A shoulder small arm with a spiral inside its long barrel to make the projectile spin during it's trajectory.
rifling marks : The marks formed on a bullet as a result of its passage along the barrel of a firearm. Revolvers and self loading pistols are divided into five "types":

Steer type	Used in all of the earlier self loading pistols
Browning type	The most common with six broad grooves with narrow lands and a right hand twist.
Colt type	Used in all Colt pistols, Bayard pistols and Spanish copies of the Colt. Six broad grooves with narrow lands and a left hand twist.
Webley type	Used in all Webley revolvers. Seven broad grooves with narrow bands and a right hand twist.
Smith and Wesson type	Used in all S+W revolvers, Harington and Richardson revolvers and Iver Johnson revolvers but not used in any self loaders. Five grooves and lands of equal width with a right hand twist

Right Ascension : The celestial equivalent of Earth's longitude, beginning at a line running pole to pole and cutting through eastern Pegasus. In meteor astronomy the right ascension is handled in degrees, starting at zero degrees and advancing eastward around the sky for a full 360 degrees ending in eastern Pegasus. For the rest of astronomy, the right ascension is handled as a time measurement. Since it takes 24 hours for the Earth to rotate, the sky is divided into 24 one hour wide bands. Each hour of right ascension equals 15 degrees.
roentgen : A unit used to measure the amount of energy in X-ray (or gamma ray) beams. One roentgen is the amount of radiation which, under ideal conditions (0^oC and 760Hg), liberates 2.083 x 10⁹ ion pairs per cubic centimetre of air.
rootstock : An underground stem.
RR Lyrae stars : A class of short period pulsating variable stars that are very old giant stars found principally in globular star clusters, all with about the same mean luminosity.
rudimentary phallus : Genital folds in both male and female embryos. In males the rudimentary phallus develops into the penis. In females the phallus grows only slightly and develops into the clitoris.
Rydberg constant : 1.097 x 10⁵ cm^-1.

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S

safe system of work : A formal procedure resulting from systematic examination of a task to identify all the hazards. Defines safe methods to ensure that hazards are eliminated or risks controlled.
satellite : can be natural or artificial. The artificial are electronic devices placed into orbit to monitor and examine regions which we may not be able observe from earth. These are used routinely to monitor atmospheric ozone, ultraviolet radiation, and many other constituents. Satellite altimetry and radar interferometry are used to measure magnetic field intensity and track Antarctic ice flow.
saturated hydrocarbons : a hydrocarbon in which the maximum valencies of the carbon atoms are satisfied by single links.
saturation : the point at which the air cannot hold any more water vapour; the point at which condensation occurs. RH =100%. Saturation is where the amount of water condensing is equal to the amount of water evaporating.
Saturn (Astronomy): The sixth planet from the sun with an orbit of 29,48 Earth years, and a spin period of 10 hours, 39 minutes and 20 seconds. It has a diameter of 74,400 miles (the second largest of the planets) and a gravity equivalent to 1.07 that of the Earth. It has 21 moons and over a thousand rings. It is the least dense planet in the solar system and has no solid surface. A magnetic field was discovered around Saturn, aligned parallel to the planet's rotation axis.
scalar quantity : A quantity that is represented by magnitude only. Unlike a vector quantity a scalar quantity has no direction. Examples include mass, time and speed.
Schlieren photography : A method of observing differences of density in a transparent medium, such as air. Light from a spark is photographed as it passes through the medium; any differences in density present cause local variations in the refractive index, which show up as streaks in the photograph. The method is used for observing sound waves, shock waves and flaws in glass.
Schwartzchild radius (SR) : The radius of a contracting star at which nothing, including light, can escape from it. It then becomes a black hole. The Schwartzchild radius for the Sun is 3 km (actual radius 7x10⁸ m).
sclerotium (pl. sclerotia) : firm mass of hyphae, usually without spores, which can survive dormancy and give rise to mycelia or a fruiting body. Usually visible with the unaided eye.
scopolamine :
Scott test : A three part test for cocaine. Solution A is composed of 2% cobalt thiocyanate in one part each of water and glycerine. This is added to the suspect substance which, if it contains cocaine, will turn it blue. Confirmation can be provided by solution B which is concentrated hydrochloric acid, and which will turn the blue solution pink. With the addition of solution C, chloroform, the blue colour will reappear in the chloroform layer.
sea level : This is the average level of the ocean over the entire earth. Tidal fluctuation is taken into account when determining sea level. Mean Sea Level (MSL) is used to reference the height of structures above ground level and depth below the ocean's surface. Atmospheric pressure is also referenced from sea level. At sea level, 760mm (29.92 inches) of mercury is normally displaced by the pressure of the air column above that point on the earth.
secondary spermocyte : The daughter cells produced by the first meiotic division if the primary spermocyte during spermatogenesis.
secretin : hormone secreted by the cells of the duodenum under the stimulus of hydrochloric acid from the stomach. Secretin in turn causes the pancreas to secrete certain digestive enzymes into the duodenum.
sediment : Particles carried by water or air that are deposited in other areas or elevation are called sediment. Usually associated with water flow, sediment will accumulate at the mouth of a river or stream as it empties into a larger, slower moving body of water. Sediment deposition is also effected by particle size.
sedimentary rock :
seismic belts : The narrow distinct belts on the Earth's surface that are subject to frequent earthquakes. They usually follow the line of plate boundaries, especially along mid-ocean ridges, near young orogenic belts, along island arc systems, and along major faults.
seismology :
segregation (of alleles) : The separation during gametogenesis of paired factors influencing a single condition.
selectivity : the extent to which a method suffers from interference.
seminal vesicles : the portion of the male reproductive duct in which sperm are stored prior to copulation.
seminiferous tubules : Tubules within the testes where the male sperm are produced. Each testis contains about 1000 highly coiled seminiferous tubules.
semi-permeable (differentially permeable): Term applied to a membrane that allows some substances to pass through while prohibiting the passage of others.
sensitization dermatitis : Inflammation of the skin due to an allergic reaction to a sensitizer .
sex chromosome : The chromosomes commonly referred to as "x" and "y", whose presence in certain combinations determines the sex of an organism.
sensitivity : the ability of an instrumental method to distinguish between small differences between analyte concentrations.
sessile : Leaves or flowers connected to the stem without footstalks.
sex pilus :
shear strain : An angular measure of deformation.
short-period comets : Comets moving in orbits having periods less than 200 years.
SI multiples :

Submultiples				Multiples
Value	Symbol	Name		Value	Symbol	Name
10–1	d	deci		101	da	deca
10–2	c	centi		102	h	hecto
10–3	m	milli		103	k	kilo
10–6	µ	micro		106	M	mega
10–9	n	nano		109	G	giga
10–12	p	pico		1012	T	tera
10–15	f	femto		1015	P	peta
10–18	a	atto		1018	E	exa
10–21	z	zepto		1021	Z	zetta
10–24	y	yocto		1024	Y	yotta

sial : The Earth's continental crust, which is composed of granite rocks rich in silicon and aluminium. It is less dense than the underlying layer of sima and much thicker.
sickle cell anaemia : A hereditary disease caused by a mutant form of haemoglobin. Under low oxygen tension in the blood, red blood cells containing sickle cell haemoglobin collapse, assuming a half moon, or sickle shape. The disease is mild in the heterozygous form but greatly shortens lifespan in the homozygous dominant form.
sidereal period : The time taken by a planet or satellite to return to the same point in it's orbit, i.e. to complete one revolution with reference to the background stars. It can be determined from the body's synodic period.
siemens (S): Unit of electrical conductance equivalent to the reciprocal of the ohm.
sigma ( S, s ):
Silurian period : A geological period lasting from about 4.45 to 4.15 x 10⁸ years ago. Conditions were mainly marine and all the first true fish appeared. The first evidence of land plants also comes from the Silurian rocks. The Caledonian period of mountain building reached it's peak towards the end of the period.
sima : The Earth's oceanic crust, which is composed of basilic rocks rich in silica and magnesium. It is denser than the sial of the continental crust and is believed to continue below it.
simple sugar : A molecule composed of a single five or six-carbon sugar. sine rule, any angle divided by the sine of the angle is equivalent to any other.
singularity (cosmology) : The point of infinite density at the central point of a black hole.
sink : a natural removal process for pollutants in the troposphere such as dissolution and removal via rain.
sintering : The heating, without melting, of a powdered substance, usually metal or plastic, so that it becomes a solid mass.
sleet : frozen precipitation that falls as little chucks of ice.
single lens reflex (SLR): a camera in which the photographer views exactly what will appear on the film. Lenses are interchangeable and close up attachments are easy to fit. They are very versatile and convenient for forensic photography. The most common type of these cameras is the 35mm. Similar in construction is the 2 ¼ inch which offers a larger film format. This will give a sharper picture than the 35mm and is therefore good for forensic photography.
small-arms : Short range, low weight firearms, originally defined as capable of being handled by one individual, they include pistols, submachine guns, rifles, grenades and shotguns. An artificial calibre ceiling of 0.6 inches, in some classification systems 20mm has had to be abandoned with the introduction of small rockets and anti-tank guided missiles.
smallpox : a severe infectious viral disease, controllable by cowpox vaccine.
smog : a term used to describe a mixture of smoke and fog. Smog occurs when high concentrations of moisture is combined with smoke (often containing oxides of sulfur and nitrogen) in the presence of high temperatures or thermal inversions and the absence of wind. These conditions cause polluted air to stagnate over industrial areas and can create a respiratory health hazard. Large coastal industrial centers with surrounding high ground are more prone to smog. There is often a diurnal (over a day) variation in the process of smog formation because one of the necessary components for its formation is sunlight.
smoke : the product of incomplete combustion and consisting mostly of carbon and small liquid and solid particles. Smoke is primarily caused by the burning of wood, coal, gasoline, or other biomass. Smoke particles are usually less than 1.0 micrometers in size. Wind intensity, particle size, air temperature, and atmospheric pressure all effect how smoke behaves in the environment.
Snell's law : When a ray of light passes from one medium to another the angle q between the refracted ray and a line normal to the interface between the media is related to the angle (i) of the incident ray, also taken to the normal, by the equation sin i/sin r = n, where n is the relative refractive index of the media.
SOCO ( Scene Of Crime Officer ) :Police Officer involved in case.
sodium dodecyl sulphate (SDS) : A detergent that disrupts most protein-protein and protein-lipid interactions.
solar longitude :This is an angular measurement that specifies the location of Earth in its orbit around the sun. More precisely, it is the longitude of the sun as given in geocentric coordinates. The evaluation of meteor data strongly relies on this figure rather than a conventional date.
solar radiation : This is electromagnetic radiation (light energy) emitted by the sun. This energy is transmitted through space in the units of electromagnetic energy called photons. The strength of the solar energy that reaches our outer atmosphere is called the solar constant and has a value of approximately 2.0 calories per minute per square centimeter. Roughly one-half (1.0 cal min^-1 cm^-2) of all the solar radiation that enters the upper atmosphere is available at the earth's surface. Of the fifty percent loss, approximately 32 percent is reflected back into space by either clouds, dust, or aerosols; the remaining 18 percent is absorbed by clouds, dust, water, and atmospheric gases. The short high-energy wavelengths that are absorbed by the Earth are re-radiated at longer, lower energy wavelengths mostly in the IR wavelength region. These lower-energy wavelengths are, in part, prevented from escaping into space by the greenhouse gases in the atmosphere. Solar radiation is the fuel source that provides a mechanism for all biological processes on earth. Without solar radiation, life on earth would not exist. (This statement, of course, neglects the contribution to the earth's surface temperature from radioactive decay in the earth.)
Solar system : A system comprising the sun and the astronomical bodies gravitationally bound to the sun, that is the nine major planets, heir satellites, ad the immense numbers of minor planets, comets and meteoroids. Almost all of the mass of the solar system (99.86%) resides in the Sun. The planets orbit the sun in the same direction and, with the exception of Pluto, move in paths close to the Earth's orbit (i.e. close to the ecliptic) and the suns equator. This and other information is taken as evidence of the common origin of the sun and the planets, some 4600 million years ago, following the contraction and subsequent flattening of a rotating cloud of interstellar gas and dust.

Body	distance from sun (x106 m)	sidereal period	spin period	radius (km)	no. of satellites	mass (kg)	mean density
Sun	---	---	25.38d	696000	9	1.99 x1030
Mercury	58	88 d	59d	2434	---	3.3 x 1023	5490
Venus	108	225 d	244d	6052	---	4.9 x 1024	5246
Earth	150	365 d	1d	6378	1	6 x 1024	5517
Moon	---	---	---	1738		7.4 x 1022	3342
Mars	228	687 d	24h	3395	2	6.4 x 1023	3937
Jupiter	778	11.86 y	10h	70866	12	1.9 x 1027	1363
Saturn	1430	29.5 y	10h	60016	9	5.7 x 1026	696
Uranus	2870	84 y	10h	25402	5	8.9 x 1025	1335
Neptune	4500	165 y	15h	22300	2	1 x 1026	1570
Pluto	5900	248 y	6.4d	3200 (2750)	---	6.6 x 1023	4800 (7900)

Solar Wind : The outflow of charged particles from the solar corona into space. Because of the high temperature of the particles of the corona (mostly protons and electrons), they are moving at speeds higher than the solar escape velocity. At the orbit of the Earth, these particles are moving at about 500 km/sec. Some of these particles are captured by the magnetic fields of the planets, forming their magnetospheres.
soluble RNA : see transfer RNA
solute : The substance that is dissolved by a solvent.
solvent : That part of the solution that is present in the largest amount, most often the part that, if pure, is normally liquid.
somatoplasm : A term used to describe all the cells of an organism except for the reproductive cells(germ plasm). In each generation the somatoplasm is derived from the germ plasm of the previous generation, but is distinct from it in that changes in somatoplasm (body cells) will not be passed on to the next generation.
somites : Paired, block like masses of mesoderm arranged in a longitudinal series along the side of the neural tube of the embryo. Each somite will form one vertebra and its associated muscles.
sorption : A class of processes by which one material is taken up by another. Absorption is refers to the process of the penetration of one material into another; adsorption to the action of one material being collected on another's surface.
sound : A disturbance propogated through a medium by longitudinal waves. Strictly the term applies only to those waves that are audible to the human ear, i.e. with frequencies between about 20 and 20,000Hertz, those with frequencies above 20,000 Hz being called ultrasound and those below 20 Hz being called infrasound. Sound is propogated by vibrations of molecules in the medium, producing fronts of compression and rarefaction. Sound waves are longitudinal as the molecules vibrate in the direction of propagation. The three basic principles of sound are it's pitch (the frequency of the wave).
sounding : a temperature profile of the atmosphere measured by a radiosonde. Also can indicate wind and dew point.
sound intensity : The rate at which sound energy is propagated through a unit area perpendicular to the direction of propagation. It is measured in watts per square metre. The intensities of two sound levels are compared by a unit called a decibel. The intensity of a sound is not the same as its loudness, the latter being the magnitude of the sensation produced by the human ear, which is dependent upon the frequency of the sound.
sound, speed of : 760 mph or 332 m^-s
space time continuum : A co-ordinate system that has four dimensions, three representing physical space and the fourth time. The four dimensional space-time continuum is used in relativity to define an event. For example an event occurring on the sun would be observed at different times on Earth and on Jupiter, as the light from the Sun takes some 35 minutes longer to reach Jupiter than to reach the earth. Thus the concept of simultaneity requires a four dimensional co-ordinate system to define events without ambiguity.
spathe : The large bract that envelops certain flowers before opening.
special creation : An account of the origin of life and its diverse forms by some act of divine creation.
specialisation (of cells) : The change in cell capability from the performance of a wide variety of functions to concentrate on one activity or set of activities.
speciation : The process by which the accumulated effects of variation within a population make cross breeding between two given organisms difficult or impossible.
species : The smallest unit of taxonomic classification, referring to the most part a group of individuals capable of breeding amongst themselves. Species are defined by morphological, ecological, physiological, and biochemical criteria.
specific gravity (relative density): The density of a substance divided by the density of water at 4^oC. This value is numerically one thousandth of the density.
specific heat capacity (c) : The quantity of heat needed to raise a unit mass of substance by 1^oC. It is measured in joules per Kelvin per kilogram. For gasses the specific heat capacity at constant pressure (cp) exceeds that at a constant volume (cv) as heat is required to do work against the surroundings during the expansion. The rate of cp/cv (symbol: y) is 1.66 for monoatomic gases, 1.4 for diatomic gases and about 1 for other gases.
speculum : A patch of brightly coloured feathers on a ducks wing. spectroscopy, The analysis of light by which the chemical make up of the light source can be identified by the dark lines created by individual elements within the light spectrum.
spectrum : In general the way in which a particular property of a system is distributed over it's components. The visible spectrum, for example, is observed in a rainbow, which shows the distribution of frequencies when sunlight is split up into it's components by raindrops. The visible part of the spectrum however is only a small part of the electromagnetic spectrum, which ranges from X-rays to radio waves.
spherical aberration : the tendency of a lens to focus the rays of light passing through the centre at one point while focussing rays from the outer portion at a different point.
Many photographic lenses have six or more elements that have been introduced to cancel both colour and spherical aberrations. This is especially true for special lenses such as fast ( wide aperture ) lenses.
spontaneous combustion : Combustion that results when materials undergo atmospheric oxidation at such a rate that the heat generation exceeds heat dissipation and the heat gradually builds up to a sufficient degree to cause the mass of material to inflame.
spontaneous generation : A concept according to which living organisms develop from non-living matter.
sporodochium (pl., sporodochia) : cushion-shaped mass of hyphae covered with conidiophores.
spring equinox : In the Northern hemisphere, March 21 or 22; on these dates, the rays of the sun are striking vertically at noon at the equator (0 degrees latitude), for the earth is in such a position in its orbit that the axis is tilted neither toward nor away from the sun. For latitudes above the equator, the dates are earlier then these dates.
squamous (pavement) epithelium : Epithelium composed of flat nucleated scales of various shapes, usually polygonal and varying in size. These cells fit together by their edges, like the tiles of a mosaic pavement.
SS/Fix ( Signed Speed Fix ) : Method of sealing certain types of item packaging that could otherwise be easily tampered with, such as CJA and SSPB packaging. Uses a sticky label with the sealer’s initials and date, covered by sellotape.
stability : possessing the ability to return to its original position; suppresses convection.
standard solution : Any solution of known concentration.
star : a luminous celestial body that is composed of gas and that derives it's energy from thermonuclear reactions in it's hot dense core. The Sun is a typical star. Stellar mass usually ranges from about 0.05 to 60 times the suns mass. A star's mass determines it's luminosity, surface temperature, size, and other properties as well as it's evolutionary path and lifetime: the higher the mass, the brighter, hotter, and larger the star and the shorter it's life. During the course of their history stars evolve, a process called stellar evolution. Young stars evolve from the protostar stage when they begin to generate energy by the thermonuclear fusion of hydrogen to form helium. This continues for some 10¹⁰ years for stars of solar mass but for only a few million years for the most massive stars. When the hydrogen is exhausted, stars evolve into giant stars, those of near solar mass becoming red giants. Further thermonuclear reactions occur involving fusion of helium, and possibly the heavier elements in more massive stars. A low-mass star finally evolves into a white dwarf. More massive stars explode as super-novae, the surviving cores possibly forming neutron stars or black holes depending on mass. Stars are not distributed uniformly through the universe but are grouped into enormous assemblies, called galaxies, as a result of gravitational forces.
starch : The principle reserve carbohydrate of plants.
star cluster : A group of stars that are associated by gravitational effects and that shared a common origin. Open clusters are loosely bound asymmetrical groupings of up top a few hundred stars occupying the disc of our Galaxy. Globular clusters are compact spherical groupings containing many thousands of very old stars and occur in the galactic halo.
static equilibrium : A state of balance in which there is no activity. statistical analysis, The use of mathematics to determine whether deviations from a pattern, as predicted by a hypothesis, are correct.
steady state theory : The model that holds that new matter is created in the spaces between the moving galaxies, so as to keep the density of the universe constant.
steam explosion : Overpressure associated with the rapid expansion in volume on instantaneous conversion of water to steam.
steering : directing other motion. The jet stream steers surface storm systems.
Stefans constant (s) : 5.67 x 10^-8Jm^-2 s^-1 degK^-4
steradian (sr) : The SI unit of solid angle equal to a solid angle that encloses a surface on a sphere equal to the square of its radius.
stere : metric unit of volume equal to one cubic metre.
steroids : A class of compounds containing four fused hydrocarbon rings.
stibium (St): The original name given to Antimony.
stimulus : Any physical or chemical change in the environment which brings about a change in the activity on the part of an organism (or portion of an organism, such as isolated tissue).
Stoke's law : The resisting force acting on a sphere, radius r, moving through a fluid under gravity with velocity v is 6prhv, where h is the viscosity of the fluid. This law is used in the determination of viscosity.
strain (physics) : The deformation of a body when it is subjected to stress.
strangeness : A property of matter expressed as a quantum number (s), postulated to account for the unusually long lifetime of some hadrons. In the quark model strange hadrons contain the strange quark or it's antiquark. Strangeness is conserved in strong interactions and electromagnetic interactions.
stratified epithelium : Several layers of cells superimposed on top of one another and varying greatly in shape. The cells of the deepest layer normally columnar and forming a single layer. Above these are several layers of spheroidal cells, becoming more compressed up to the superficial flattened cell layer.
stratocumulus clouds : Low altitude gray colored clouds composed of water droplets that have a patchy appearance. Each cloud patch consists of a rounded mass. This cloud has a somewhat uniform base and normally covers the entire sky. Between the patches blue sky can be seen.
stratopause : The boundary between the stratosphere and the mesosphere. It occurs at a height in the atmosphere of approximately 50 kilometers; however this depends on latitude. The atmosphere is characterized by a decrease in pressure with respect to increased altitude. More importantly, regions within the atmosphere like the troposphere, stratosphere, and mesosphere are distinguishable because of distinct temperature gradients with relatively well-defined starting and ending points. The stratopause is the highest portion of the stratosphere, with a temperature of approximately 0^oC; the stratopause can also be described as the warmest region between the mesosphere and the stratosphere.
stratosphere : The thermal atmospheric region of the atmosphere between the troposphere and the mesosphere. The lower boundary of the stratospheric region is marked by the tropopause and begins at approximately 13 kilometers; however, this altitude of the troposphere depends on latitude. The upper limit of the stratosphere is marked by the stratopause at approximately 50 kilometers. The stratosphere is characterized by relatively stable temperatures (between -80 and -50 degrees Celsius) in the lower regions, and begins warming near 20 kilometers, reaching its maximum temperature of approximately 0^oC at the stratopause. Stratospheric chemistry is of particular interest to scientists because ozone, the principal substance that shields the earth from incoming solar ultraviolet radiation, is found in the stratosphere. It should also be noted that wind currents in the stratosphere are primarily horizontal in nature.
stratospheric clouds : These are clouds found in the stratospheric region of the atmosphere. Unlike the moisture laden troposphere, the stratosphere is almost moisture free. A lack of moisture means that cloud formation in the stratosphere is a relatively uncommon occurrence. Because of the very low temperatures, nacreous clouds, a type of stratospheric cloud, occur during winter conditions at the higher latitudes. A second type of stratospheric cloud, called a polar stratospheric cloud (PSC), occurs in the polar regions during winter and early spring. Polar stratospheric clouds are of particular interest to scientists studying the Antarctic Ozone Hole. Polar stratospheric clouds form under extremely cold conditions, whereby nitric acid, water vapor and other trace chemicals freeze to form ice crystals. PSCs provide a solid surface on which chlorine-containing reservoir compounds can gather, and on this surface the chemical reactions involved in the depletion of ozone are greatly increased.
stratospheric ozone : This is also called the ozone layer, where ozone concentrations are as high as 10 parts per million, and is a vitally important region of the atmosphere. This layer of ozone is located approximately 20-50 kilometers above the earth's surface. Stratospheric ozone is important because it prevents most of the high-energy ultraviolet solar radiation from reaching the earth's surface. Photodissociation, a photochemical process, is responsible for the formation of the protective ozone layer in the stratosphere. In the upper atmosphere, diatomic oxygen absorbs high-energy ultraviolet radiation. The absorption of radiation causes the diatomic oxygen molecule to break forming two oxygen radicals. The oxygen radical can then recombine with other diatomic oxygen molecules to form triatomic oxygen, or ozone. In the middle regions of the stratosphere, ozone is found in concentrations as high as 10 parts per million. Ozone can also form in the lower portions of the troposphere, due to anthropogenic activity and by a completely different mechanism. Without the protective stratospheric ozone layer in the upper atmosphere, life (as we know it) on earth would not be possible.
stratus cloud : In general, clouds are classified and named according to their appearance and altitude at which they occur, being either high, medium, or low. Stratus clouds are low clouds, and as the root word suggests they are layered in appearance. They occur in broad sheets across most or all of the sky. Generally their formation is due to condensation within layered air that is not subjected to strong vertical movement.
strychnine : An alkaloid poison derived from plants of the genus Strychnos. It acts upon the C.N.S., causing convulsions and ultimately death. It is still used as a poison for pests such as moles.
styrene : chemical formula C8H8, also commonly called vinyl benzene. Styrene is an aromatic hydrocarbon originating from petroleum and natural gas by-products. It is used to manufacture resilient, lightweight packaging materials and fiberglass. Styrene is extremely volatile in air and evaporates quickly; as a result, it does not remain in the atmosphere for long periods of time.
sublimation : The evaporation of a substance without melting. For any substance the liquid phase only occurs within certain limits of temperature and pressure - if the pressure is low enough, heating a solid will result in sublimation. Substances that sublime at atmospheric pressure include carbon dioxide (dry ice) and iodine.
sub-machine gun : A light short range small arm developed from the infantry light machine gun. They are more accurate than the pistol and smaller than the rifle. They almost all use 9mm ammunition, fire automatically, and depend on blow-back action (i.e. use the expanding gas of the ammunition to activate the reloading mechanism).
subsidence : sinking air.
substrate : The molecule upon which an enzyme acts during an enzyme catalysed reaction.
succession : Ecological development that begins in a habitat or area not previously occupied by the given community of a previously unoccupied area.
Secondary succession : refers to the replacement of one community by another.
sucrose : A carbohydrate consisting chemically of one molecule each of glucose and fructose linked together. It is commercially the most important of the sugars, being used as a sweetener in food and drinks. When heated to 160^oC it forms barley sugar and at 200^oC becomes caramel.
sulphur dioxide : This is a colorless gas consisting of a single sulfur atom and two oxygen atoms. Sulfur dioxide is a major primary pollutant in the atmosphere originating mostly from coal fired power plants and other fossil fuels combustion. In the atmosphere, sulfur dioxide is usually oxidized by ozone and hydrogen peroxide to form sulfur trioxide, a secondary pollutant. Sulfur trioxide, similar to sulfur dioxide, is extremely soluble in water. If these sulfur oxides are present in the atmosphere when condensation occurs, droplets of sulfuric acid (acid rain) are formed. Volcanic eruptions provide a natural source of sulfur dioxide in the atmosphere. However the real problem associated with the production of sulfuric acid in the atmosphere is not with the sulfur dioxide expelled by volcanoes. Anthropogenic production of sulfur dioxide, caused by the burning of fossil fuels, is largely responsible for damage caused by acid rain.
sulphuric acid : In the atmosphere sulfur oxides (see sulfur dioxide) are converted to sulfuric acid. Oxides of sulfur and nitrogen combine with atmospheric moisture to produce acid rain. Although some sulfur oxides are introduced into the atmosphere by natural means, such as volcanic eruptions, the majority of the sulfur oxides responsible for the damaging effects of acid rain come from anthropogenic sources, mainly the burning of fossil fuels. Areas in the northeastern United States, eastern Canada, and northern Europe have suffered damage due to the effects of acid rain. In many areas damage to forests, crops, lakes, and streams are so severe that they are completely devoid of any life forms. Steps are now being taken in many parts of the world to reduce the amount of sulfur dioxide introduced into the atmosphere. In 1990, amendments where made to the Clean Air Act that places restrictions on the release of sulfur dioxides by power plants. The amendment calls for the reduction of sulfur emissions from a 1990 level of nearly 20 million tons per year to approximately 10 million tons per year by January 1, 2000.
summer solstice : In the Northern Hemisphere occurs on about June 21 of each year. The summer solstice is the longest day of the year and marks the beginning of the summer season. If the earth's axis were not tilted in relation to the plane of earth's orbit around the sun (the ecliptic) there would be no seasonal changes on earth. But because the earth's axis is tilted in relationship to its plane of orbit around the sun (~23.5 degrees) and assumes a constant direction, with the North Pole pointing towards the North Star, seasons occur, and daylight hours can fluctuate in length. Each day prior to the summer solstice the sun appears farther north in the sky; but at the summer solstice, the sun reaches its most northerly position in the sky, directly above the Tropic of Cancer, 23.5 degrees north latitude. Following the summer solstice the sun moves farther south in the sky, and on about September 23 it is directly overhead at the equator (the fall equinox).
Sun : the nearest star to the Earth and the centre of our Solar system. It dwarfs the other bodies, having a diameter of 864,000 miles and representing approximately 99.86 percent of all the mass in the solar system. As a star, the Sun generates energy by the process of fusion. The temperature at it's core is 15 x 10⁶ K, and the pressure there is 340 billion atmospheres. The surface temperature is 5,500^oC. At the solar core, hydrogen can fuse into helium, producing energy. The Sun consists of three layers: the photosphere, the chromosphere, and the corona, and spins on it's axis from left to right.
sunspot cycle : This cycle, lasting an average period of 11 years, involves recurring increases and decreases in the number of sunspots that occur on the sun's surface.
sunspots : A dark area, which is strongly magnetic, that occurs in the area of the photosphere on the disk of the sun.
supercell : a large thunderstorm in which the updrafts and downdrafts are in such close balance that the storm may have a lifetime of several hours. supercooled water, water that is below the freezing temperature but is still in liquid form.
supercooling : The reduction of a temperature of a liquid below its freezing point without it's solidification. The effect can be achieved by slow and continuous cooling with pure liquids, since any solid matter would cause the liquid to solidify around it. A super cooled liquid is in a meta-stable state and any disturbance will cause solidification.
superfluid : A fluid that exhibits a very high thermal conductivity and virtually no friction at temperatures close to absolute zero. Such a fluid will flow up the sides and out of an open container. Liquid helium becomes a superfluid at 2.19 Kelvin's, called the lambda point.
supergiant : The largest and most luminous type of star, bright enough to be visible in nearby galaxies. They evolve from very massive but more complex stars are very rare.
supernova : A cataclysmic stellar explosion, seen as a sudden increase in the e stars brightness by a million times or more. It occurs in the late evolution of stars, one type almost certainly involving a massive supergiant stars, another type, possibly disrupting white dwarfs. Most or all of the stars substance is blown off at high velocity, forming an expanding gas shell - the supernova remnant. If the stars core survives it will most probably end up as a neutron star or a black hole.
Svedberg unit : Unit used to describe in multiples of 10-13 sec. the velocity attained per unit of applied force by a particle moving though a liquid medium.
syllogism : A logical scheme or analysis of a formed argument, consisting of three propositions called respectively the major premise, minor premise and the conclusion. e.g. Every virtue is commendable, patience is a virtue, therefore patience is commendable.
symbiosis : A relationship between two species of organisms in which both derive benefits from the other.
syndactyly : Commonly called "webbed Fingers", where the digits are joined together with skin. A rarer form of this can occur when the fingers are fused together by the bone.
synodic period : The average time taken by a planet or satellite to return to the same point in its orbit, relative to the sun, as seen from earth or from the satellites primary (i.e. the body it orbits).
synoptic scale : a large scale event that is usually measured in hundreds to thousands of kilometres and days to weeks; e.g. fronts, cyclones, and anticyclones.
synthesis : The process by which larger molecules can be built up from smaller molecules or atoms.
system : An association of independent organs throughout the body for the performance of a necessary body function. Some systems in higher animals are the circulatory, digestive, muscular, skeletal, and excretory systems.
systematic errors : an error which affects all measurements equally, making all measurements either higher or lower than the true value.
systematics : A term originally used to refer to the study of different systems of classifying animals and plants. Today the term "systematics" is used more or less synonymously with the term taxonomy.

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T

tail : the most distinctive feature of comets, especially great ones. It is typically directed away from the sun. Ancient and medieval observers frequently described a comet as a broom or sword, depending on the look of the tail. Typically, telescopic comets will exhibit either no tail or one extending a few arc minutes. Naked-eye comets can show a tail extending up to several tens of degrees. Comets can display two basic types of tails: one gaseous and the other largely composed of dust. The dust tail can be curved, spread out, and yellowish in appearance, while the gas tail is usually very straight and bluish.
tamper evident bag : type of packaging used by certain police forces for submitting items to the FSS. Method of sealing is such that the SS/Fix is not required.
tap root : A stout, elongated, primary root.
tau ( T, t ) :
tau particle : An elementary particle with a very short lifetime (5x10-12 sec.) and a mass about 3500 times that of the electron. It is classified as a lepton. It reacts by weak interaction.
tautology : A statement that is always true and therefore gives no information. For example "IT is either raining or it isn't."
taxonomy : The science of classification; in biology this refers to the classification of organisms into kingdom, phylus, class, order, family, genus and species.
tectonic activity : The process of the formation, movement, interaction, and destruction of parts of the earth's crust on a generally large scale. This can be used to explain seismicity, volcanism, and mountain building.
tectonics : The structural arrangement of rocks in any crust of a planet. Used to understand rock structures.
teleology : Assigning purpose to an action, such as saying the cell takes in Calcium ions "in order to...."
temperature inversion : The abnormal reversal of temperature in the troposphere caused by the entrapment of urban air pollution. Under normal circumstances, air in the troposphere is cold at high altitudes and warm at low altitudes, or near the earthís surface. When air pollutants, such as SO₂ or NO_x, in urban areas get too concentrated, smog is produced. Since cold air underlies the warmer air at high altitudes, the air does not mix well which can lead to human health disturbances in people with respiratory illnesses such as asthma.
tendon : The sinew joining muscle to a bone.
telophase : The final phase of mitosis, in which the cytoplasm of the dividing cell is cleaved and two daughter cells are formed.
tera (T) : 10¹²
teratogen : a chemical or physical agent that can cause defects in a developing embryo or foetus when the pregnant female is exposed to the harmful agent.
terminal burst : The flare at the end of a meteor's path.
territoriality : The tendency of some organisms to defend a section of space surrounding them and/or their family.
termolecular reaction : A reaction containing three particles. In the atmosphere an example of a termolecular reaction is one in which a molecule acquires the excess energy released by a reaction so that the products created do not convert back to the original state of the reactants. The reaction of molecular oxygen with an oxygen atom (radical) to produce ozone is a good example of an important atmospheric termolecular reaction. In the atmosphere this third body is most often molecular nitrogen because statistically this is the most likely next collision since atmospheric N₂ = 78% by volume.
terpene : A naturally occurring organic compound, of the general empirical formula, C₁₀H₁₆, biologically built from a naturally occurring "monomer" called isoprene, C₅H₈, which is found as a volatile oil in plants. A clearly important, and olifactorily obvious, example is alpha-terpinene found in lemon oil.
tertbutyl alcohol : a highly flammable, volatile, colorless liquid which has a camphor-like odor. It is miscible in esters, and aromatic and aliphatic hydrocarbons, and soluble in water. Based on its vapor pressure, tert-butyl alcohol will exist mainly in the vapor phase in the atmosphere. It is most likely to react with the hydroxyl (OH) radical at this state. The reaction products are formaldehyde and acetone.
Tertiary Period : This extended from about 65 million years ago to about 2.5 million years ago.
Tertiary period : The first geological period of the Cainozoic era lasting from about 65 to 1.8 x 10⁶ years ago and contains the Pleistocene, Eocene, Ogliocene, Miocene, and Pliocene epochs, in ascending order. Most of the rocks of the period were laid down in shallow water. Modern invertebrates and mammals evolved and became increasingly abundant; the modern angiosperms became the dominant plants. The Alpine period of mountain formation extended through the period and reached it's peak in the Miocene. The climate began to deteriorate in the Oligocene, finally leading to the ice age of the Pleistocene.
tesla : The SI unit of magnetic flux density equal to one weber per square metre and equivalent to 10,000 gauss.
testosterone : An androgen; a hormone produced in the interstitial cells of the testes of males and responsible for the characteristic changes associated with puberty.
tetrad : In meiosis, the four part structure resulting from the duplication of each pair of homologous chromosomes.
thermacidophiles : Bacteria which grow optimally at 105^oC and at pH2.
thermodynamics : That branch of physical science which deals with heat as a form of energy. It is concerned with such problems as the exchange of energy (measured always in respect to the gain or loss of heat from a system) during chemical or physical processes.
thermodynamics : The science of heat and temperature and of the laws governing the conversion of heat into mechanical, electrical, or chemical energy.
thermosphere : The outermost shell of the atmosphere, between the mesosphere and outer space; where temperatures increase steadily with altitude.
theta ( Q, q ) :
thickness : the vertical distance between two levels of constant pressure. The greater the average temperature of the layer, the "thicker" it is.
threshold limit value – ceiling ( TLV-C) : limit for the atmospheric concentration of a chemical which may not be exceeded at any time, even instantaneously in workroom air.
threshold limit value – short term exposure limit ( TLV – STEL ) : A maximum limit on the concentration of a chemical in workroom air which may be reached, but not exceeded, on up to four occasions during a day for a maximum of 15 minutes each time with each maximum exposure separated by at least one hour.
threshold limit value – time weighted average ( TLV – TWA ) : A limit for the atmospheric concentration of a chemical, averaged over an 8hr day, to which it is believed that most people can be exposed without harm.
thylakoid disc : Flattened pancake like sacks with double layered walls, formed from the inner membrane system of the chloroplast. The lamellae and grana inside chloroplasts are composed of thykaloid discs.
thymine :
time dilation : An effect produced by Einstein's special theory of relativity. If two observers, A and B, are moving at a velocity v, relative to each other, it will appear to a that Bs clock will show that time is running more slowly; thus a time t, measured on A's clock, will be t(1 - v2/c2)0.5 on B's clock, where c is the velocity of light.. The effect has been observed in some particles moving at high velocities which appear to have an anomalously long lifespan.
tissue : An aggregate of similar cells bound together in an ordered structure and working together to perform a common function.
TNT (trinitrotoluene, C₆H₂(NO₂)₃CH₃ ) : A highly explosive pale yellow crystalline solid. It is prepared from toluene treated with concentrated sulphuric and nitric acids and is used in shells, bombs, etc., and blasting explosives.
toluene : a highly volatile and water-soluble benzene derivative that is highly toxic to most forms of life. Its estimated lifespan in air is 60 hours in the case of a photochemical reaction with hydroxyl radical and is eventually oxidized to carbon dioxide. Toluene is used in a variety of industries including the manufacture of TNT, pharmaceuticals, rubbers, and other benzene derivatives, and is also a fuel additive and a paint solvent. Toluene also reaches the atmosphere from natural sources such as coal tar, mineral oils, and forest fires.
torr : The pressure of air that supports 1mm of mercury in a barometer at sea level. 1 atm = 760 torr = 101.325 kPa.
total column ozone : The total amount of ozone that is found in a column of air above the earth from the surface to the top of the atmosphere. The majority of this amount is typically found in the stratosphere.
total inhalable dust : The fraction of airborne dust which enters the nose and mouth during breathing and is available for deposition in the respiratory tract.
toxic air pollutants : in the atmosphere, toxic air pollutants are present in small amounts that can have adverse effects on the health of human populations and the environment. Toxic air pollutants include polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides, polychlorinated biphenyls (PCBs), and heavy metals, such as, mercury, copper, lead, zinc, arsenic, and cadmium. These pollutants are carried by particulate matter and can be mixed with precipitation. The Integrated Atmosphere Deposition Network (IADN) studies the transportation of specific toxic substances located in the atmosphere.
trace gases : These are gases in the atmosphere that do not occur in large quantities but are significant to life on Earth or are important constituents of the chemical cycles in the atmosphere.
trade winds : Wind systems occupying most of the tropics, which blow from 30 degrees North and South toward the equator; winds are northeasterly in the Northern Hemisphere and southeasterly in the Southern Hemisphere.
trajectory : The flight path of a missile dependent upon the speed of the missile, the air resistance acting upon it, the forces exerted by gravity and any wind pressure pushing it laterally.
transamination : The stepwise series of reactions in which the amino groups from one amino acid type is transferred to an intermediate substance, thus producing another type of amino acid.
transduction : the transfer of genes between bacteria by bacteriophages.
transfer RNA (soluble RNA) : A type of RNA in the cytoplasm of which there are at least 20 varieties, one specific for each amino acid. tRNA unites with its specific amino acid and draws it to the ribosome during protein synthesis.
transformation : a mode of gene transfer in bacteria in which a piece of free DNA is taken up by a bacterial cell and integrated into the recipient genome.
transitional epithelium : Epithelium in which the cells , in three or four layers, are so fitted together that the appearance is not one of distinct stratification. Found in the ureters and urinary bladder of humans.
translation : An aspect of protein synthesis in which the genetic information coded on messenger RNA is used top specify the order of amino acids in a polypeptide. Translation occurs in the ribosomes, where messenger RNA, ribosomal RNA, and activated amino acids meet and peptide bonds are formed.
transmitted lighting :
transmutation : The conversion of one element into another. They were achieved eventually by bombarding elements with alpha particles or neutrons. An example is the production of oxygen 17 when nitrogen 14 is bombarded with alpha-particles.
transmutation (of species) : An older term for the idea that over a long period of time new species arise though modification of old species.
transuranic elements : Elements with a higher atomic number than uranium. Apart from traces of neptunium and plutonium, none of them has ever been detected in nature since no isotopes of sufficient half life exist: they have been created since 1940, usually in minute amounts, in nuclear reactions.
trefoil (botany) : A simple form of division.
Triassic period : A period of geological time at the beginning of the Mesozoic era, lasting from about 2.4 to 2 x 10⁸ years ago. The rocks of the period, laid down mainly under continental conditions often considered with those of the preceding Permian period as the Permo-Triassic. The dinosaurs, ichthyosaurs and plesiosaurs appeared in the Triassic.
tribology : The study of friction and such applied topics as lubrication, abrasives, surface wear, etc.
trichloroethylene (C₂HCl₃) : this is an industrial solvent used primarily for vapor degreasing and cold cleaning. It is an extraction solvent for greases, oils, fats, waxes, and tars, and is used by the textile processing industry to sour cotton, wool, and other fabrics. Exposure to moderate amounts of trichloroethylene may cause various health effects such as headaches, vertigo, visual disturbance, tremors, and dizziness. Death may occur from inhalation of large amounts. People located near or downwind of sites where TCE may be in operation might be exposed to higher levels. It is a carcinogen.
trichlorofluoromethane (Freon -11) : One of the principal greenhouse gases, a gas with absorption bands in the infrared portion of the spectrum. There is extensive evidence showing that a class of synthetic compounds, the chlorofluorocarbons (CFCs), are responsible for the destruction of the ozone layer. CFCs are molecules that contain one or more atoms of both chlorine and fluorine. In September of l992, the ozone hole over Antarctica was the largest ever recorded and was almost THREE times as large as the area of the U.S. Because CFCs are so unreactive, they do not break down when released into the air in the troposphere where they are spilled. In time, air currents and diffusion carry them into the stratosphere, where, under the influence of UV radiation, they release chlorine radicals that initiate the destruction of ozone. Data collected by NASA have shown conclusively, that there is an inverse relationship between ozone concentration and the chlorine monoxide radical in the stratosphere; ClO is formed by chlorine atom attack on O₃. CFCs are very useful inert, nontoxic, nonflammable compounds that had been used for years as coolants and as spray can propellants for aerosol forms of hair sprays and deodorants. They had been unsurpassed as solvents for cleaning electronic microcircuits. Commercially, the most important CFCs are the halogenated methanes, Freon-11 (trichlorofluoromethane) and Freon-12 (dichlorodifluoromethane). Over 50% of asthma inhalers contain chlorofluorocarbns as the solvent and gaseous propellent. These CFCs have relatively recently been prohibited in all products except in those medicinal inhaler dispensers for asthmatics and a few other limited exceptions. In Finland alone there are over a million medicinal dispensers that disperse freons into the atmosphere. This is equal to the freon concentration of the cooling devices in approximately l00,000 refrigerators.
Trojan group : Minor planets that lie close to either of two points in Jupiter's orbit. Each point forms an equilateral triangle with Jupiter and the Sun.
trophic level : Levels of nourishment in a food chain. A food chain is the transfer of energy from its ultimate source in plants through a series of organisms, each of which eats the preceding organism.
trophoblast : In mammals the thin walled side of a blastocyst which gives rise to the placenta and the membranes that surround the embryo.
tropopause : The area where the temperature in the troposphere no longer decreases, indicating the boundary between the troposphere and the stratosphere.
troposphere : The lowest layer of the Earth's atmosphere, ranging from the ground to the base of the stratosphere with a altitude of 10-15 kilometers depending on the latitude. This is where all weather occurs. The word troposphere is derived from the Greek words tropos, turning and spharia, sphere.
trough : an area of low pressure. Cyclonically curving winds.
tuber : The fleshy underground part of the stem of a plant.
tunnel effect :
twin lens reflex camera :

Tyndall effect : When a parallel beam of light, such as a wavelength that none is absorbed, is passed through a gas, liquid, or transparent solid, part of it is scattered in all directions so that it may be seen from the side.

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