APHIDS

DEFINITION. any of a large family (Aphididae) of small, soft-bodied homopteran insects that suck the juice from plants.

On a stem or on the underside of a leaf sometimes a crowded colony of plant lice, or aphids, may be visible. They are parasites that have sharp sucking beaks and live on the sap of plants. There are many kinds. Most feed exclusively on a particular crop, weed, or tree.

The smallest aphids measure about 1/20 of an inch (0.13 centimetre) in length and the largest about 1/14 of an inch (0.64 centimetre). Most species are green, but some are pink, white, brown, or black. Those that migrate are born with wings. Most generations are made up of wingless females. During the feeding season these females, without mating, produce living young that are all females and that themselves produce several generations of young during the summer. In the fall a generation is born that includes both males and females. After mating, the females of this generation lay eggs that will hatch in the spring to start new colonies.

Aphids secrete from the alimentary canal a sweet watery liquid that is called honeydew. Ants relish this as food. Some species of ants care for whole herds of aphids (so-called "ants' cows"). The ants build mud shelters for them at the roots of plants and move them often to new pastures as the old ones wither. To induce the flow of honeydew the ants milk the "cows" by stroking them with the antennae. Most aphids, particularly the woolly aphids, spread a white, waxy secretion over themselves for protection.

Many aphids suck plant sap or inject poisonous saliva into plants, causing the plants' leaves to curl and sometimes drop off. Some aphids produce gall-like swellings on roots and bark. One of the most destructive aphids is the green bug, which infests oats, wheat, and other small grains. Fields of corn are often destroyed by the corn-root aphis, which is dependent on the cornfield ant for survival.

Aphids reproduce so rapidly that if unchecked they can destroy entire fields of crops. Their numbers may be controlled by such natural enemies as ladybird beetles (ladybugs), aphid lions, and lacewings. Farmers frequently control the insects by spraying with pest-control agents. Aphids belong to the order Homoptera and the family Aphididae.

MIMICRY - close resemblance, in colour, form, or behaviour, it serves to disguise or conceal the organism from predators

Helen Zille sounding like an African

A fascinating result of evolution is the phenomenon of mimicry, the superficial resemblance of one organism to another that gives the mimicking organism some advantage or protection from predators. Many plants and animals have evolved such resemblances in order to increase their own chances of survival. A walking stick, for example, is an insect that closely resembles the twig of a plant. By virtue of this similarity, or mimicry, it often remains unnoticed by predators. The chameleon is a tree-dwelling lizard that is able to change its body colour to blend in with a variety of backgrounds.

Monarch butterfly, insect (Danaus plexippus) of the order Lepidoptera, family Danaidae; breeds on milkweeds.

Biologists have distinguished between several types of mimicry. In 1861 the English naturalist Henry Walter Bates described a form of mimicry in which the mimic takes advantage of the defences of its model. Such mimicry is called Batesian mimicry. In a well-known instance, the monarch butterfly serves as the model. The monarch is extremely distasteful to many birds; in fact, a bird that eats the monarch will often vomit shortly after its meal. Consequently many otherwise predatory birds will shun the monarch. The viceroy butterfly, which is not distasteful itself, has assumed colouring and markings very similar to the monarch, and thus many birds will avoid it as well. Another example is the harmless snake caterpillar, which can mimic the body and movement of a snake to discourage its natural predators.

Another style of mimicry was described in 1878 by the German zoologist Fritz Muller. In Mullerian mimicry two similar species derive mutual benefits from their resemblance. For example, two wasps, the sand wasp and the yellow jacket, are very similar in appearance, and both can inflict a painful sting. A predator that encounters either the sand wasp or the yellow jacket will learn to associate their colouration with pain and will thenceforth avoid preying on either species.

Anglerfish, marine fishes of the order Lophiiformes with lure-like appendages for baiting prey.

In yet another form of mimicry, called aggressive mimicry, a predator mimics a harmless organism in order to catch its unwitting prey. One aggressive mimic, the angler fish, lies motionless in the water while waving a small fishlike appendage. When a would-be predator approaches to eat the bait, it becomes a quick meal for the angler fish. Another fish, the sabre-toothed blenny, mimics the colour and behaviour of the harmless cleaner wrasse, which feeds on parasites attached to other fish. The blenny uses this resemblance to get close enough to its prey to attack it before it can recognize the deception.

The European cuckoo exhibits a type of parasitic mimicry. It lays its eggs in the nest of a bird whose eggs are similar in appearance. The host bird then raises the cuckoo's young.

Mimicry is the product of natural selection. Mimicking organisms have developed their particular similarities over time. Each step of the organism's transition has given it some slight advantage that has increased its chances for survival. For example, a change in colouration that allows a predator to camouflage itself may increase its chances of sneaking up on its prey. Thus it is able to acquire more food and increase its chances of staying healthy, surviving, and reproducing. Evolutionary biologists have used mimicry as a research tool and to help prove Charles Darwin's theory of evolution. They can trace the evolution of mimicking organisms to learn how long the model and mimic have shared a habitat and to what selective pressures the two organisms have adapted.

Assisted by Elliot Mitchell.

WASPS - any of various families of winged hymenopteran insects

Most people think of wasps only as bugs with bad tempers and sharp stings. Actually, wasps exhibit remarkably sophisticated behaviour and are often helpful, especially to farmers, because they help to check the population of other insects that may be harmful to crops. The many species that feed on nectar travel from flower to flower just as bees do and so are significant as pollinators of various plants. In spite of their reputation, wasps sting humans only when threatened, frightened, or provoked.

Wasps are members of the insect order Hymenoptera, which includes ants, bees, and sawflies. Besides the large and commonly known kinds of wasps, there are a wide variety of small and solitary species. In all, wasps comprise about one-third of the more than 100,000 species in the order.

Wasps characteristically have two pairs of clear, membranous wings, the back pair slightly smaller than the front. Most wasps are strong flyers, but some, such as the female velvet ants, are flightless. As with other insects, the wings and six legs are attached to the middle segment of the body, the thorax. The rear segment, the abdomen, is generally elongated, and the connection between the thorax and abdomen is usually quite narrow. The head has a pair of compound eyes, which form multiple images, and usually three simple eyes, which form single images. The antennae are straight, flexible, and usually composed of 12 or 13 segments. The mouth parts consist of mandibles and maxillae. Mandibles are great, short jaws that are toothed at the tips. Maxillae are smaller mouth parts located behind the mandibles.

Not all species of wasps have stingers. Furthermore, because the stinger is actually a modified ovipositor (a structure used for laying eggs), it is present only in female wasps. The stinger is usually tucked into the tip of the female's abdomen and is connected to a venom gland. When the wasp stings its insect prey, it injects a poisonous substance that paralyses or kills the victim. Some wasp species that do not sting use their ovipositors to inject their eggs directly into a host insect or plant.

Most wasps are predatory and feed primarily on other insects, including other members of their own order. Their larvae are frequently voracious parasites that eat insects or spiders supplied by the mother wasp. This habit of acquiring animal food to feed their larvae distinguishes these wasps from bees, which nourish their young on plant material.

Wasps may be divided into two groups the social wasps and the solitary wasps though there are species that exhibit characteristics of both.

Social Wasps

Social insects, those living in communities and having differentiated forms or castes, as queens, workers, drones.

These species live in colonies in which responsibilities are divided between three castes: a fertilized female or queen, female workers (usually sterile), and fertile males. In the temperate regions of the world the general reproductive pattern of these wasps begins in the spring when a single queen begins to build a nest in which to lay her eggs. As she builds, other females of the same species join her but remain only as assistants that aid in the construction, food gathering, and care of the larvae. Generally only the original queen is allowed to lay eggs, and she will eat any eggs laid by the accessory females. When the first larvae have become adults, the queen drives away the other females.

This first generation of young is composed exclusively of females whose ovaries are non-functional and who act strictly as workers. They continue with the construction of the nest, care for the next generation of young, forage for food, and feed the queen and each other. It is the second generation of young, emerging in the autumn, that produces the fertile males and females. Shortly thereafter the males are driven from the nest and the young females follow them to be inseminated. Eventually all members of the colony die except for the fertilized queens. They hibernate through the winter, and in spring begin the reproductive cycle again. In the tropics some of the social wasps do not die seasonally, so colonies may persist for several years.

Paper wasp, insect (Polistes fuscatus) of the order Hymenoptera, family Vespidae.

Among the more common social wasps in North America are the hornets and yellow jackets. The female workers of these species, though small, are fiercely protective and highly venomous. Bronze coloured paper wasps are another variety of social wasp. These species and a number of others build their nests from a paper like material made by the wasps themselves. The "paper" consists of plant materials that are chewed and regurgitated by the wasps then stroked into fine strips and glued together.

The hornets are known to build extensive, elaborate nests. They select a location in the branches of shrubbery, in hollow trees, under the frameworks of houses, or in subterranean sites such as mouse nests. First the queen attaches one hexagonal cell to the ceiling by a little stalk, with the opening down. After a week she has created a small plate of five to ten cells. Later, when the numerous workers join in the construction, the nest grows to an impressive size. In subterranean nests the hole may be considerably enlarged to permit expansion. New levels of the comb are added progressively from the top down, with pillars connecting the different tiers. Then the combs are completely covered by a balloon like envelope that may be either elastic or brittle. The single opening, for entrance and exit, is located at the bottom; it also serves as the ventilation hole. The multi-layered envelope both protects the hive and assists in temperature regulation.

Temperature, degree of hotness or coldness measured on a definite scale.

Wasps also are capable of regulating the temperature of the nest themselves. Even on autumn nights when the outside temperature falls to 50 F (10 C), the interior of the nest stays within a half degree of 86 F (30 C). The females accomplish this by moving their flight muscles while keeping their wings motionless, thereby generating heat from their metabolic activity to warm the nest. If, on hot summer days, the outside temperature rises above the 86 F (30 C) optimum for the wasps and their brood, the workers cool the nest by bringing in water and causing it to evaporate by beating their wings.

Solitary Wasps

Most wasps are solitary and harmless. They do not live in colonies, and most do not defend their nests from intruders. Usually these species lay their eggs inside single cells constructed to house the larva and its store of food through the pupation stage (the cocoon phase before the larva emerges as a full adult). Most female wasps lay in a supply of paralysed insects for the larvae to feed upon when they hatch, then seal the entrance to the cell. The insect meals are usually preserved alive to ensure a supply of fresh food for the larvae. Some reports indicate that, if uneaten, these victims may remain paralysed and helpless, but still alive, for as long as four months. After the larva has consumed its ready-made meal, it pupates, and emerges the following summer as a full adult.

Many species of solitary wasps are unusually selective in their choice of the prey they feed their larvae. They may specialize in hunting one particular victim to the exclusion of all others. Surprisingly enough, it seems to make no difference to the larvae they have been known to thrive on an artificial diet. Nevertheless the females continue their single-minded pursuits. One species even hunts only winged female ants, ignoring the many female ants that have already discarded their wings. Naturalists are still at a loss to explain why this wasp then bites off the wings of the captured ants before placing them in her nest.

Representatives of almost all insect orders appear on this select list of prey of the various wasp species. For example, the ensign wasps hunt only cockroaches; the mud daubers only spiders; cicada killers only cicadas; digger wasps only beetle larvae; potter wasps only caterpillars; and the particular bee-killer wasp pursues only the honeybee.

Gall (or gall nut), abnormal growth on leaves, stems, buds, flowers, or roots of plants caused by various parasites, especially insects and mites, and more rarely by nematodes, bacteria, fungi, slime moulds, and algae; found on almost all forms of plant life, but especially common on oak trees, willows, roses, and goldenrod.

The gall wasps, which lay their eggs in the tissues of plants, select not only a particular species of tree or shrub, but also particular parts on the host plant. The developing larvae are a major source of plant galls, or tissue swellings. Those plants commonly affected include the oak trees and rose plants. However, though the galls are unsightly, they ordinarily do little harm to the plants because they are relatively small and localized.

Some species of solitary wasps prefer not to expend their energy on nest building, hunting, and child care. They are noted for smuggling their eggs into the cells of other wasps, a practice called brood parasitism. The cuckoo wasps, small, flying wasps with bright metallic green or blue colouring, are among the most beautiful of the order Hymenoptera, and they are all parasites. The female usually lays her eggs inside the nests of bees, thread-waisted wasps, or yellow jackets. If she is caught in the act and attacked, she rolls herself into a ball to protect herself from the nest owner's stings. Finally she is thrown from the nest and left for dead; she emerges unscathed. If the cuckoo wasp is successful in laying her egg, the host does not notice the deception. When the cuckoo wasp larva hatches, it eats the host's larvae along with any food stored for them. It then spends the winter as a pupa and emerges in the spring as an adult.

Another group of parasitic wasps, the velvet ants, are common in most parts of the world, particularly in the Southern and South western United States. Despite their name, the velvet ants are not true ants. They were mistakenly named after the females, which are wingless. Many members of the species are brightly coloured often scarlet or yellow. The largest members of the velvet ants, the so-called cow killers, are bright orange or red.

They reach lengths of up to 1 inch (2.5 centimetres) and have stingers that are almost half again the length of the body. Like the cuckoo wasps, the velvet ant is a parasite that lays its eggs in the nests of other insects. Although the velvet ants generally select other wasps or bumblebees to act as hosts, a variety of other insects have been identified as their hosts, including mud daubers in North America, bumblebees in Europe, and tsetse flies in Africa.

Wasps exhibit a wide range of behaviours, not all easily categorized. Some non parasitic solitary wasps check on their larvae regularly, bringing them fresh stores of food whenever necessary and sealing the nest only when the larvae have pupated. Others lay their eggs on temporarily paralysed hosts, then leave the young to fend for themselves. In the latter case the unfortunate host, having regained the use of its limbs, continues about its business undaunted until the larvae hatch and begin to consume its body. Another species of wasp exhibits a highly unusual form of social parasitism. The parasitic queen invades the nest of a colony of social wasps, demotes the queen to worker, and assumes her throne. In this case the former queen lays no more eggs, the host wasps care for the offspring of the conqueror, and the host species dies out without descendants.

Wasps are found throughout the world on every continent except Antarctica and on all major islands. Several thousand species of wasps occur in North America, but wasps are most numerous and their species most diverse in tropical areas. Some of the parasitic wasps are the smallest insects in the world, reaching maximum lengths of less than 0.008 inch (0.02 centimetre). The largest wasps reach lengths of more than 2 1/4 inches (6 centimetres).

The stinging wasps belong to the suborder Apocrita of the order Hymenoptera, the non stinging wasps to the suborder Symphyta. The majority of the social wasps belong to the family Vespidae, and can be distinguished from most other wasps by the way they fold their wings like a closed fan along their back when at rest. Many members of the Vespidae are black with bright yellow or white cross bands or other markings. Hornets and yellow jackets belong to the subfamily Vespinae, whose members are widespread throughout North America, Northern Africa, Europe, and Asia. The paper wasps belong to the subfamily Polistinae, which contains more than 150 species throughout the world.

The families of solitary wasps are numerous and varied. The ensign wasps belong to the family Evaniidae, the mud daubers and cicada killers to the family Sphecidae, digger wasps to the family Scoliidae, and potter wasps to the subfamily Eumeninae of the family Vespidae. Other wasp families include the Cynipidae (gall wasps), Chrysididae (cuckoo wasps), and Mutillidae (velvet ants).

Assisted by J. Whitfield Gibbons, Senior Research Ecologist and Professor of Zoology, Savannah River Ecology Laboratory, University of Georgia.

SPECTRUM AND SPECTROSCOPE (Part 1 of 3)

From earliest times the rainbow had delighted and puzzled observers. Men invented myths to explain the beautiful arc of multicoloured light that appeared after the rain. But a scientific answer to the puzzle of the rainbow did not come until 1666. In that year Sir Isaac Newton began investigating the problem of eliminating the colour fringes in telescope lenses. (Scientists now call these colour fringes chromatic aberration.) He decided that the trouble might lie in the character of light itself. So he began to study how light formed colours.

He admitted a small beam of sunlight into a darkened room and passed it through a prism. The beam produced a band of colours just like the rainbow, ranging from red through yellow, green, and blue to violet. He then passed each of these colours through other prisms and found that they did not change. But when he passed the whole band of coloured lights through a prism in reverse position, the coloured band became white sunlight again.

From this he reasoned that white light is really a mixture of coloured lights, and that each colour is bent by a different amount when it passes through the prism. This difference in bending enables each colour to stand out separately and be visible. The band of coloured lights thus formed is called a spectrum. The rainbow is actually a spectrum, formed by sunlight passing through raindrops.

Separating light into its colours is called dispersion. It is accomplished by refraction (bending) of light in the prism. Each of the colours has its own wavelength. The wavelength determines how much each colour will bend. Red bends the least, violet the most. If the light beam strikes the prism at a certain angle, the amount of bending for each colour is always the same. Each colour then falls in exactly the same place on a screen, so its position is enough to identify it.

Scientists use the dispersive action of the prism in the spectroscope. The spectroscope reveals that the spectral pattern of light is different for various classes of light sources.

Light from the sun, from certain lamp filaments, and from molten metals each produces a spectrum which has all colours in an unbroken array. Such a pattern is called a continuous spectrum. Incandescent gases give off only certain colours, in fine lines. Their spectra are called bright-line spectra. Both bright-line and continuous spectra are emission spectra, produced by emitted light.

Fraunhofer, Joseph von (1787-1826), German optician and physicist; worked to improve optical instruments; invented a heliometer and a micrometer.

In the early 1800s Joseph von Fraunhofer observed that the continuous spectrum was crossed by many dark lines. He charted more than 700 of them, but he was unable to explain their meaning. Because of his discovery, however, they are called Fraunhofer lines.

Kirchhoff, Gustav Robert (1824-87), German physicist, born in Konigsberg, East Prussia (now Kaliningrad, Russia); developed spectrum analysis and discovered caesium and rubidium (with Bunsen); explained the Fraunhofer lines; professor of physics at Heidelberg 1854-74, at Berlin 1874-87.

The meaning of the Fraunhofer lines was discovered about 50 years later by Gustav Kirchhoff and Robert Bunsen. With a spectroscope they studied the spectra of certain substances which were vaporized in the non luminous Bunsen burner flame. Each vapour showed a characteristic bright-line spectrum. But when emitted light was passed through a cooler vapour of the same substance, the bright lines were replaced by dark ones in the same position.

This replacement of bright by dark lines meant that the second vapour had absorbed the characteristic light of the first. Later experiments showed that the cooler vapour absorbs those light waves which it would normally emit at a higher temperature. In 1859 Kirchhoff published his findings in his laws of radiation and absorption. The spectral pattern thus formed is called a dark-line, or absorption, spectrum.

Kirchhoff and Bunsen also noticed that characteristic arrays of lines are given off by the different chemical elements. For example, incandescent sodium always gives certain yellow lines near the middle of the spectrum, and no other element gives these lines. Thus when these lines appear, sodium must be present in the incandescent substance. If the lines are bright the light has come directly from the incandescent sodium. If they are dark the light has passed, somewhere along its path, through an absorbing vapour containing some gaseous sodium. Only minute quantities of an element are needed to make its lines appear. This makes it possible to identify the elements in unknown substances.

These discoveries not only explained the Fraunhofer lines in the spectrum of sunlight but made it possible to determine what chemical elements the sun contains. The absorption necessary to produce the dark lines was considered as taking place in the outer layers of incandescent gas surrounding the sun. For "analysis" of the sun, the dark lines could be compared with the bright-line spectra of different elements produced in the laboratory. Whenever they corresponded, scientists could be sure that the element existed in the sun.

Stars likewise could be "analysed" as to chemical contents by this method.

Janssen, Pierre-Jules-Cesar (1824-1907), French astronomer, born in Paris; discoverer of helium in sun; founded and directed observatory on Mont Blanc 1893.

Lockyer, Joseph Norman (1836-1920), British astronomer and physicist, born in Rugby, England; pioneer in application of spectroscope to sun and stars; explained sunspots; between 1870 and 1905 conducted eight British expeditions for observing total solar eclipses ('The Sun's Place in Nature'; 'Recent and Coming Eclipses'; 'The Chemistry of the Sun'; 'Inorganic Evolution').

Ramsay, William (1852-1916), British chemist, born in Glasgow, Scotland; professor Bristol University 1880-87, University of London 1887-1913; discoverer of helium, neon, krypton, xenon; co-discoverer of argon; research in radioactivity led to new theory of transmutation of elements; knighted 1902; received 1904 Nobel prize.

Cleveite, mineral, oxide of uranium and lead; named for Per Theodor Cleve, a Swedish chemist; produces helium when heated with acid.

Scientists have obtained spectra corresponding to the different elements and have measured and charted every line. When they wish to learn the composition of a star, they photograph its spectrum and then check the lines against these charts for the elements. A notable triumph of the method was the discovery of helium. In 1868 P.J.C. Janssen (1824-1907), a French astronomer, and the English astronomer, Sir Norman Lockyer (1836-1920), independently discovered lines in the solar spectrum which could not be identified with the charted lines of any known element. Lockyer interpreted this to mean that an element unknown to us existed in the sun. He named it helium, after helios, Greek for "sun." Then in 1895 Sir William Ramsay (1852-1916) found that the Norwegian mineral cleveite, when heated, gave off minute quantities of a light gas which he identified as helium by means of its spectrum.

Measuring Light Waves

Millimicron (mm), unit of wave length equal to one millionth of a millimetre or one thousandth of a micron; sometimes used in the measurement of light waves.

Angstrom unit (A, or A.U.), ten-millionth of a millimetre, used to describe length of light waves; named to honour Anders Jonas Angstrom.

Nanometre (nm), measuring unit in spectroscopy, equalling one billionth of a meter.

The units once commonly used to measure wavelengths were the millimicron, denoted by the symbol mm and equalling one millionth of a millimetre; and the Angstrom unit (A or A.U.), one ten millionth of a millimetre Wavelengths are still measured in various units, but the unit most commonly used in spectroscopic work today is the nanometre (nm), which is equal in length to the unit it replaced, the millimicron. This is one of the special units which science has accepted as a means of avoiding the excessively long decimal fractions which would be needed to express wavelengths as short as those of light, if measured in inches or centimetres For example, violet light has a wavelength of 410 nanometres. The following table gives the wavelengths which fall approximately in the centre of each of the coloured regions in visible light:

Violet 410 nanometres

Blue 470

Green 520

Yellow 570

Orange 620

Red 710

Since the colour of light is determined by its wavelength, this means that the shorter the wavelength the more the light is bent by passage through a given prism. Thus the wavelength (and the frequency) of the vibration causing the wave is judged from the amount of bending given by the prism. This is determined by the position of the spectral line on the screen or photographic plate.

Prism and Diffraction-Grating Spectroscopes

Modern spectroscopes used in very technical fields vary considerably in function and design and are often quite specialized for the specific substances they analyse However, the fundamental teaching instruments generally used in today's classrooms are the relatively simple prism spectroscopes. These consist of a collimator (tube for admitting light), a glass prism, and a telescope. The collimator has a slit at one end to admit light and a lens on the other to concentrate it. The lens directs the light on the prism, which disperses the ray into its component colours Sometimes a train of prisms is used to increase the dispersion.

After the colours leave the prism they are focused on the object glass of the telescope. Each wavelength appears as a separate image of the collimator slit. When the telescope is replaced by a camera to photograph the lines, the device is called a spectrograph.

Rowland, Henry Augustus (1848-1901), U.S. physicist, born in Honesdale, Pa.; professor Johns Hopkins University 25 years; determined ohm and the mechanical equivalent of heat; discovered magnetic effect of electric convection.

A more powerful type of spectroscope uses a diffraction grating, invented by Fraunhofer in 1821. He made it by twisting a fine wire about two tiny screws. With it he measured the wavelengths of light with surprising precision. The modern precision grating consists of a plate of speculum metal or glass upon which fine lines, equidistant and parallel, have been ruled. Among the finest of these are the gratings made by H. A. Rowland. He invented a machine to rule the entire grating automatically, etching from 14,000 to 20,000 lines per 1 inch (2.5 centimetres). By means of such a grating, made on a concave surface, Rowland secured a spectrum band of sunlight more than 20 feet (6 meters) long. The grating uses a special application of the interference phenomenon of light.

Diffraction-grating spectroscopes can measure the wavelength of light with a precision of .000,000,000,001 centimetre (10^-12 centimetre). It is used as the dispersing medium in analysing visible light and ultraviolet rays. A photographic plate is usually used as the detecting device in the analysis.

Motion, Temperature, Magnetism

Doppler effect, law in physics discovered by Christian Doppler (1803-53); applied to sound, light, and radar from moving sources.

The spectroscope can also tell the astronomer whether a star is moving toward or away from the Earth by means of a phenomenon known as the Doppler effect. Everyone has noticed how the whistle of an approaching locomotive rises to a shrill note as it approaches then drops to a lower and lower tone as the train rushes away. The reason for this is that when the train approaches, its whistle is nearer to us each time a sound wave is emitted.

The successive waves reach us a little more quickly and therefore have a higher pitch. When the train is receding, the waves are dragged out, and thus the pitch of the whistle is lowered.

Similarly, when a star moves toward the Earth, each light wave is shortened a little. Consequently, the lines shift their position toward the violet end of the star's spectrum.

When the star is moving away from the Earth, the wavelengths are lengthened somewhat, and the lines in the spectrum shift a little toward the red end. The amount of shift reveals the speed of the star's motion; but since light in a vacuum travels at the tremendous speed of 186,282 miles per second (299,743 kilometres per second), the star must be travelling at a very great speed to create a noticeable effect.

Temperature, degree of hotness or coldness measured on a definite scale.

Temperature and pressure have certain effects on spectra. These effects can be detected and used to determine the approximate temperature of stars and the pressure of gases on distant bodies.

Zeeman, Pieter (1865-1943), Dutch physicist; professor physics and director Physical Institute, University of Amsterdam, 1900-35; discovered the Zeeman effect of magnetism on light; Nobel prize 1902.

Another marvellous revelation of the spectroscope is the connection between magnetism and light. In 1896 the Dutch physicist Pieter Zeeman (1865-1943) discovered that when light passed through the field of a strong electromagnet, the lines in the resulting spectrum were split into two or more lines. This influence of magnetism on light, which was named the Zeeman effect after its discoverer, has proved to be valuable in the detection and measurement of magnetism in the sun.

The Electromagnetic Spectrum

The coloured lights in the rainbow make up but a small portion of that huge spectrum of energy called electromagnetic radiation. The other groups include radio waves, microwaves, infra red light (heat), ultraviolet rays, X rays, and gamma rays. Despite the different effects they produce, each of these forms of energy travels through space as an electromagnetic disturbance. They are sometimes called forms of radiant energy.

SPECTRUM AND SPECTROSCOPE (Part 2 of 3)

Study of the lines in various spectra has helped build the modern theory of matter. Soon after Bunsen and Kirchhoff developed the use of spectral lines as a means of chemical analysis, scientists thought that the various lines were given off by atoms vibrating at different rates under the stimulus of heat. They believed that the faster vibrations resulted in the shorter waves that caused lines to appear toward the violet end of the spectrum.

Rydberg, Johannes Robert (1854-1919), Swedish physicist; worked on the spectrum.

In 1885 Johann Jakob Balmer (1825-98) discovered through experimentation that the various rates of vibration in a mass of glowing hydrogen bore a simple mathematical relation to each other. This indicated that some one type of "mechanism" was at work at varying rates within the hydrogen atom, giving off the different wavelengths. Balmer could not guess what this "mechanism" might be, however. Then Johannes Robert Rydberg (1854-1919) introduced further information on this subject and developed a formula named for him that described many more observed relations; but he also did not know what it was within the atom that vibrated. Finally, the answer came in 1913 from Niels Bohr (1885-1962), the renowned Danish physicist.

Bohr's theory, built largely upon knowledge from the study of radioactivity, held that the hydrogen atom consisted of an electron revolving like a planet around a central nucleus, or "sun." Bohr believed further that as an atom absorbed energy by being heated, for example this orbit would enlarge by definite amounts, each enlargement representing the absorption of one quantum, or "packet," of energy. When energy was emitted, as in the form of light, the electron would fall by steps into inner orbits, and the frequency of the light would depend upon how many orbits were traversed. If the electron fell inward by one orbit, the "energy splash" resulting from this would travel outward as light of a certain frequency. If it fell inward by two orbits, light of a different frequency would go forth. The collection of lines given by hydrogen in a spectroscope sums up these actions taking place in all the hydrogen atoms present. Furthermore, by using the Planck constant (the fundamental measurement of a quantum) and electrical factors in a formula of the Rydberg type, Bohr was able to reduce his whole explanation to terms of electrical force. Thus the spectrum of hydrogen was explained as the product of electrical forces within the atom, and the spectroscope became useful for studying the structure of matter.

Another significant discovery was that X rays could be made to give spectra just as visible light did. This was done by causing a beam of X rays to fall upon a crystal. The short rays of the X rays were diffracted in a pattern that revealed the arrangement of atoms in the crystal.

SPECTRUM AND SPECTROSCOPE (Part 3 of 3)

Moseley, Henry Gwyn-Jeffreys (1887-1915), British physicist, born in Weymouth, England; gave his name to the Moseley number.

In 1913 and 1914 the English physicist H.G.J. Moseley (1887-1915) announced the discovery of far-reaching relations among X rays produced from the surfaces of different metals by the impact of electrons. He found that each metal gives certain groups of X-ray lines, corresponding to certain frequencies. As he passed from a lighter to a heavier metal, each successive element showed lines of higher frequencies. Moseley reasoned that this was not due to increasing atomic weight, since several substances of different atomic weights showed the same spectra. It must have been due to a regular increase in the number of orbiting electrons, corresponding to the atomic number, of the atoms of the metals. Moseley's work provided the basis for the modern periodic classification of elements.

Modern Applications

Spectroscopes are used in almost every technical field, especially for identifying constituents and processes in any source that emits light. In some industries many similar samples must be analysed quickly and simultaneously for their light-absorbing characteristics. A physician may have several hundred samples of blood serum to analyse in a short period of time. Fortunately, fully automated analytical spectroscopes are available. New techniques of analysing samples based on how they absorb radiation to differing extents have given scientists new ways to determine a substance's properties.

Infra-red spectroscopy, ultraviolet spectroscopy, and nuclear magnetic resonance spectroscopy are the most commonly used of such techniques.

In the 20th century, scientists discovered that all atomic particles behave as if they had wavelengths much like those of light waves. Spectroscopes were used to study these particles. The study of the various elementary particles themselves is divided into baryon and meson spectroscopy, and elementary-particle spectrometers are used for such studies.

One of the accomplishments of neutron spectroscopy, another field, was the plotting of the structure of large complex molecules like those of DNA and RNA, the basic materials of heredity. Furthermore, spectroscopes are used to measure temperatures in controlled thermonuclear fusion.

EASTERN ORTHODOX CHURCHES

In the year 1054 a major split occurred in Christianity. The churches in Western Europe, under the authority of the pope at Rome, separated from the churches in the Eastern Roman (or Byzantine) Empire, under the authority of the patriarch (bishop) of Constantinople. The churches of the Eastern Empire have come to be known by the collective term Eastern Orthodoxy. The word orthodoxy simply means "correct teaching," or "right belief." The official designation is actually Orthodox Catholic Church to set it off from the Roman Catholic church.

AD 395: Division of the Roman Empire. Emperor Theodosius I died in 395. He had appointed two successors: his older son, 17-year-old Arcadius, was given rule over the east; and his younger son, 10-year-old Honorius, was given authority in the west. Honorius ruled from Milan, however, not from Rome.

This division of the Roman Empire between Arcadius and Honorius was meant to be temporary, but it became permanent. The Eastern Empire, more commonly called the Byzantine Empire, took on a life of its own, while the empire in the West disintegrated under the impact of barbarian invasions until it collapsed in the 5th century. The Eastern Empire endured until 1453, when it was conquered by Ottoman Turks. It contributed much to civilization through the arts, particularly its fabulous mosaics. Its most famous ruler was Justinian I, creator of the Code of Justinian, a collection of past imperial decrees that influenced legal theory for centuries to come.

The two parts of the old empire differed religiously, too. In the West the leadership of Christianity was gradually assumed by the bishop at Rome, the pope. In the East, the patriarch of Constantinople was the head of Christianity. This separation pushed Christianity in two different directions, until a split occurred in 1054, when the religion was divided between Roman Catholicism in the West and Eastern Orthodoxy in the East.

AD 726: Iconoclastic Controversy One of the chief divisions in early Christianity arose over the issue of icons. An icon is a religious image, usually a depiction of a saint. Those who opposed the use in churches of images such as statues charged that it was a pagan custom.

They thought that people attached too much importance to the icons and came to believe that the icons had their own powers, rather than merely representing the power of God.

In 726 the Byzantine emperor Leo III banned the use of images, launching the Iconoclastic, or "image-breaking," Controversy. Five years later the Roman pope Gregory III threatened to excommunicate all iconoclasts. The argument within the churches lasted until 843 and fuelled the already bitter differences between the Western church, based in Rome, and the Eastern church, based in Constantinople. The two churches Roman Catholic and Eastern Orthodox finally broke with each other in 1054.

1054: East-West schism in Christianity. The final split separating the Eastern Orthodox and Roman Catholic churches came in 1054, after centuries of disagreement. In this year Pope Leo IX and Patriarch Michael Cerularius excommunicated each other.

One source of contention concerned the use of images, or icons, in churches. Another dispute centred on the authority of the Pope, who is the bishop of Rome, over the churches. As hopes of reconciliation faded, the patriarchs of the Eastern churches gradually renounced allegiance to Rome and paid homage to the Patriarch of Constantinople as the "first among equals."

The schism has never been healed, but in the 20th century the two large branches do have relations with one another. Most Orthodox churches have joined with Protestant denominations to form the World Council of Churches, established in 1948, but the Roman Catholic Church is not a member.

Organization

Patriarch (from Greek, meaning father and rule), father and ruler of a family or tribe; in biblical history applied particularly to Abraham, Isaac, and Jacob; in Roman Catholicism term used to signify a bishop of the highest rank, and in Greek church a high dignitary, such as the patriarch of Constantinople.

Eastern Orthodoxy is a fellowship of autonomous, or independent self-governing, churches, each of which is under the rule of a bishop. The patriarch of Constantinople (now Istanbul) is considered the first among equals, but he has no authority comparable to that of the Roman pope.

Union of Soviet Socialist Republics (commonly called Soviet Union, formerly Russia), from 1917 to 1991 country of e. Europe and of w.-central and n. Asia; cap. Moscow. Circa 1995.

Turkey (officially Republic of Turkey), country of Asia and Europe; 301,380 sq mi (780,570 sq km); cap. Ankara, lying in Asia; pop. 58,584,000. Circa 1995.

The number of independent churches has varied throughout history. Today there are the Church of Constantinople, the Church of Alexandria (Egypt), the Church of Antioch (head quartered at Damascus, Syria), the Church of Jerusalem, the Russian Orthodox church, the Church of Georgia, the Church of Serbia, the Church of Romania, the Church of Bulgaria, the Church of Cyprus, the Church of Greece, the Church of Albania, the Polish Orthodox church, the Ukrainian Orthodox Church, and the churches of the Czech Republic and Slovakia. There are also smaller autonomous churches in Finland, Crete, and Japan and many in the United States. Many of the churches existed in hostile surroundings. The Russian Orthodox church suffered severe persecution in the past. It was forced to cooperate with the authorities of the Soviet Union in order to function until the restructuring of Communism allowed open worship after 1990. The church in Albania has been outlawed altogether. The members of the churches in Turkey, Egypt, and the Middle East live as minorities amid large Muslim majorities. Eastern Orthodoxy in the United States is represented by almost every national Orthodox body.

The Orthodox understanding of the church is based on the principle that each local community of Christians, gathered around its bishop and celebrating the Lord's Supper, or Eucharist, is a local realization of the whole church on Earth. This concept of wholeness is called catholicity. This may seem an abstract concept, but what it means essentially is that everything necessary to be a church is found in the local congregation. The idea of catholicity may be compared to a loaf of bread. Each single slice is not the whole loaf, but each slice has all the ingredients necessary to be bread. Hence, wherever a bishop and congregation are gathered together, there is the church.

This continuity of the church is demonstrated by the fact that the consecration of a bishop requires the presence of several other bishops. This testifies to the continuity of the whole church in the present and to its unbroken heritage from the time of the Apostles.

Besides bishops, there are two other orders of clergy priests and deacons. These may be married men, though bishops are always chosen from among unmarried or widowed clergy.

Eastern Orthodoxy also has a strong tradition of monasticism, dating back to the 3rd and 4th centuries. It has been primarily a contemplative movement, seeking to experience God through a life of prayer. There has not been the development of religious orders with missionary or educational goals as in Western Christianity.

Belief and Worship

Eastern Orthodoxy considers itself the bearer of an unbroken living tradition of Christian faith and worship inherited from the earliest believers. Its beliefs are based on consistency with the Bible and tradition as expressed in the ancient councils the seven ecumenical church councils that took place between 325 and 787. The churches also accept the decrees of some later councils as reflecting the same faith.

Lord's Supper (or Holy Eucharist, or Communion), Christian rite in which bread and wine (or grape juice) are taken in commemoration of Christ's death; sacrament was instituted by Christ at his supper (Lord's Supper, or Last Supper) with his disciples the night before his death (Bible, Matt. xxvi, 26-29; Mark xiv, 22-25; Luke xxii, 14-20).

The churches accept seven sacraments, or holy acts: baptism, chrismation (similar to confirmation), the Lord's Supper, ordination, penance, anointing of the sick (called extreme unction in the West), and marriage. This number of sacraments was never defined in the early church. It was only in response to the Protestant Reformers of the 16th century, who accepted only two sacraments, that the number seven was determined.

The sacrament of chrismation is peculiar to the Eastern churches. In it newly baptised infants are anointed with oil and immediately admitted to the Lord's Supper. In Western churches children must wait until they are older before receiving their first communion. In admitting infants the Orthodox churches maintain that baptism is the beginning of a new life that must be sustained by the Eucharist. When given communion, the bread is dipped in the wine a procedure called intinction and administered to, or placed on the tongue of, the recipient.

Liturgy (from Latin liturgia, meaning "a public service"), term applied to any or all of the services used in public worship; especially in Roman Catholic, Eastern Orthodox, and Episcopal churches.

Liturgies. Forms of worship are called liturgies. The two chief Eucharistic liturgies in the Orthodox churches are those of St. John Chrysostom and of St. Basil the Great. Both acquired their present form in the 9th century. There is also a liturgy of St. James, often used in Jerusalem. All of the liturgies are elaborate, festive occasions.

The liturgies are divided into three segments. The first is a rite of preparation, during which the priest puts on a plate particles of bread symbolizing the gathering of the saints, both living and dead, around the living Christ. This is followed by the liturgy of the catechumens, or learners. This segment includes the reading of the lessons and the sermon. Finally comes the liturgy of the faithful, or baptised Christians, which includes the recitation of the creed and the administering of communion.

The Orthodox churches follow the traditional church calendar, the church year beginning with Advent, four Sundays before Christmas. The greatest festival is Easter. The date of Easter normally varies from its celebration in the West because the Eastern churches still use the Julian calendar to compute the date.

The Orthodox churches have a rich tradition of musical composition for hymns and liturgies. Since the Orthodox tradition bans the use of musical instruments or accompaniment (with the exception of some American congregations), all singing is done without musical accompaniment.

Santa Sophia (in Greek, Hagia Sophia, meaning "holy wisdom"), building in Istanbul, Turkey, erected as Christian church in 6th century by Justinian I; became Muslim mosque in 1453; in 1935 was made a museum of Byzantine antiquities.

Architecture. Some of the most beautiful and highly decorated church buildings in the world have been built by Christians of the Orthodox tradition. The first major house of worship, and still one of the great buildings of the world, was built during the reign of Emperor Justinian I in the 6th century at Constantinople. It is the Hagia Sophia, or Holy Wisdom. It consists of a huge round dome set atop a classical basilica-style building. Most Orthodox churches today have one or more domes. The Hagia Sophia was turned into a mosque by the Ottoman Turks, and later it became a museum.

Iconostasis, screen, or wall, in interiors of Eastern Orthodox churches.

The interior of an Orthodox church is somewhat different from other churches. In most Western churches the altar is readily visible from the entryway. But in Orthodox churches there is a screen, or wall, called an iconostasis, with one or more doors in it, largely concealing the altar area from the worshippers It is called an iconostasis because it is richly decorated with icons in the form of pictures of Christ and the saints. Orthodox churches have no statues or other three-dimensional images. The purpose of the iconostasis is to suggest a contrast between the visible manifestation of God in Christ as a man and his more perfect and invisible presence in the communion.

It is largely because of its emphasis on the gathered community in worship that the Orthodox churches have survived in often hostile surroundings. For this reason it is impossible to overestimate the significance of the liturgy in the life of the Eastern churches.