A chemical mixture is a collection of molecules or atoms of different types. A mixture is distinguished from a pure substance, which has constant composition (is composed of a only one type of molecule or atom), and a unique set of physical properties (no matter how large or small a sample is observed). The properties of a mixture depend not only on the types of substances that compose it, but als…
The cell is the smallest living component of organisms and is the basic unit of life. In multicellular living things, a collection of cells that work together to perform similar functions is called a tissue; various tissues that perform coordinated functions form organs; and organs that work together to perform general processes form body systems. The human digestive system, for example, is compos…
Cogeneration is the simultaneous generation of two forms of energy, usually heat and electricity, from one energy source. Traditional energy generating systems produce only heat or electricity by burning a fuel source. In both cases, burning the fuel generates a lot of heat and the exhaust gases can be hotter than 932°F (500°C). Traditionally, this "waste heat" would be…
Like all living things, the various types of cells in plants, animals, and the many different cell types in humans must eventually die. Cell death occurs in one of two ways. Cells can be killed by the effects of physical, biological, or chemical injury. Additionally, cells are induced to kill themselves. Cell suicide is also referred to as apoptosis (from the Greek words apo, meaning from, and pto…
Cotton is a fiber obtained from various species of plants, genus Gossypium, family Malvaceae (Mallow), and is the most important and widely used natural fiber in the world. Cotton is primarily an agricultural crop, but it can also be found growing wild. Originally cotton species were perennial plants, but in some areas cotton has been selectively bred to develop as an annual plant. There are more …
Cell division is the process where a single living cell splits to become two or more distinct new cells. All cells divide at some point in their lives. Cell division occurs in single-celled organisms like bacteria, in which it is the major form of reproduction (binary fission), or in multicellular organisms like plants, animals, and fungi. Many cells continually divide, such as the cells that line…
Cognition is a complex mental process whereby an individual gains knowledge and understanding of the world. While cognition cannot be neatly dissected into constitutive processes, psychologists point out that it reveals the interplay of such critical psychological mechanisms as perception, attention, memory, imagery, verbal function, judgment, problem-solving, decision-making, with the admixture o…
The common cold, also often referred to as an upper respiratory infection, is caused by some 200 different viruses, and has defied both cure and vaccine for centuries. The United States alone will have about a half a billion colds a year, or two for each man, woman, and child. Dedicated researchers have searched for a cure or even an effective treatment for years. The pharmaceutical company that d…
A coulomb (abbreviation: C) is the standard unit of charge in the metric system. It was named after the French physicist Charles A. de Coulomb (1736-1806) who formulated the law of electrical force that now carries his name. …
The cell is bound by an outer membrane that, in accord with the fluid mosaic model, is comprised of a phospholipid lipid bilayer with proteins—molecules that also act as receptor sites—interspersed within the phospholipid bilayer. Varieties of channels exist within the membrane. There are a number of internal cellular membranes that partially partition the intercellular matrix, and t…
Collagen is a protein found abundantly throughout the bodies of animals, including humans. In fact, collagen makes up about one-third of the total body weight. Collagen is an important component of the body's connective tissues, which perform a variety of functions in the body. These tissues provide the framework, or internal scaffolding, for various organs such as the kidneys and lymph nod…
Convergent evolution represents a phenomenon when two distinct species with differing ancestries evolve to display similar physical features. Environmental circumstances that require similar developmental or structural alterations for the purposes of adaptation can lead to convergent evolution even though the species differ in descent. These adaptation similarities that arise as a result of the sa…
A colloid is a type of particle intermediate in size between a molecule and the type of particles we normally think of, which are visible to the naked eye. Colloidal particles are usually from 1 to 1,000 nanometers in diameter. When a colloid is placed in water, it forms a mixture which is similar in some ways to a solution, and similar in some ways to a suspension. Like a solution, the particles …
Every set that can be counted is countable, but this is no surprise. The interesting case for countable sets comes when we abandon finite sets and consider infinite ones. An infinite set of numbers, points, or other elements is said to be "countable" (also called denumerable) if its elements can be paired one-to-one with the natural numbers, 1, 2, 3, etc. The term countable is somewh…
Medical science depends on the staining of cells in tissues to make accurate diagnoses of a wide range of diseases from cholera to sexually transmitted diseases, to parasitic diseases and skin infections. Staining techniques performed routinely in microbiological laboratories include gram's stain, acid-fast stains, acridine orange, calcofluor white, toluidine blue, methylene blue, silver st…
Respiration occurs in three stages. The first stage is glycolysis, which is a series of enzyme-controlled reactions that degrades glucose (a 6-carbon molecule) to pyruvate (a 3-carbon molecule) which is further oxidized to acetylcoenzyme A (acetyl CoA). Amino acids and fatty acids may also be oxidized to acetyl CoA as well as glucose. During electron transport, much of the energy represented by th…
Cellular telephone technology is also called cellular radio. The cellular radio network became fully operational in North America in 1978. This technology relies on the distribution of what are called cell sites over a wide geographical area. Each cell site consists of a radio transceiver and a controller that sends and receives signals from the mobile phones in the area to a telephone switch. The…
Colobus monkeys and the closely related langurs and leaf monkeys are Old World monkeys in the sub-family Colobinae of the family Cercopithecidae. The primates in this subfamily share a common trait—they lack thumbs or have only small, useless thumbs. (The name colobus comes from a Greek word meaning mutilated.) However, lack of a thumb does not stop them from nimbly moving among the branche…
Coursers and the closely related pratincoles are 17 species of birds that comprise the family Glareolidae, in the order Charadriiformes, which also contains the plovers, sandpipers, and other families of waders and shorebirds. The pratincoles occur in southern Europe and Asia, Africa, Southeast Asia, and Australasia, but coursers only occur in Africa, the Middle East, and India. Coursers and prati…
Cellulose is a substance found in the cell walls of plants. Although cellulose is not a component of the human body, it is nevertheless the most abundant organic macromolecule on Earth. The chemical structure of cellulose resembles that of starch, but unlike starch, cellulose is extremely rigid (Figure 1). This rigidity imparts great strength to the plant body and protection to the interiors of pl…
Centipedes (phylum Arthropoda, class Chilopoda) occur throughout the world in both temperate and tropical regions where they live in soil and humus and beneath fallen logs, bark, and stones. Because they lack a hard outer skeleton, centipedes are confined to moist environments in order to maintain water balance. Many species are therefore active only at night, remaining sheltered during the day. M…
Courtship is a complex set of behaviors in animals that leads to mating. Courtship behavior communicates to each of the potential mates that the other is not a threat. It also reveals information to each animal that the species, gender, and physical condition of the other are suitable for mating. Pre-mating activities are for the most part ritualistic. They consist of a series of fixed action patt…
The coypu or nutria (Myocastor coypu) is a species of semi-aquatic, dog-sized rodent in the family Capromyidae. These animals are native to central and southern South America, but they have become widely established elsewhere, mostly as a result of animals that have escaped from fur farms or that have been deliberately released. Coypus have a stout, 17-25 in (43-64 cm) long body, with a roughly tr…
Crabs are some of the best known arthropods—a terms that means jointed foot (Greek: arthron, joint; pous, foot). They are among the most successful of all living species (about 4,500 species have been described), with members adapted to living on land and in water; some species even succeed in living in both habitats. The majority, however, live in the marine environment. Unlike lobsters (t…
The first true cranes, founded on the principles of levers and counterweights, used a pulley system fixed to a single mast or boom. Lifting power was provided by humans or draft animals operating a treadmill or large wheel. Eventually, a second mast and guy wires were added to increase the strength and stability of this early form of crane. One of the most significant developments in crane design,…
A centrifuge is a device for separating two or more substances from each other by using centrifugal force. Centrifugal force is the tendency of an object traveling around a central point to continue in a linear motion and fly away from that central point. Centrifugation can be used to separate substances from each other becausematerials with different masses experience different centrifugal forces…
Cranes are tall, wading birds known for their beauty, elaborate courtship dances, and voices that boom across their wetland habitat. Their family Gruidae, is among the oldest on Earth. Today 15 crane species are found throughout the world, except in South America and Antarctica. Two species, the whooping crane (Grus americana) and the sandhill crane (G. canadensis) are found in North America. Cran…
Color is a complex and fascinating subject. Several fields of science are involved in explaining the phenomenon of color. The physics of light, the chemistry of colorants, the psychology and physiology of human emotion are all related to color. Since the beginning of history, people of all cultures have tried to explain why there is light and why we see colors. Some people have regarded color with…
Crayfish are freshwater crustaceans of the order Decapoda, which includes crabs, shrimps, lobsters, and hermit crabs. Crayfish are nocturnally active, live in shallow freshwater habitats, and feed on aquatic plant and animal life, as well as dead organic matter. Their natural predators include fish, otters, turtles, and wading birds. Crayfish are particularly vulnerable to predation during their p…
Ceramic materials are usually understood to be compounds of metallic and nonmetallic elements, though some are actually ionic salts, and others are insulators. These materials can be very complicated, as are for example clays, spinels, and common window glass. Many ceramic compounds have very high melting points. Ceramics have a wide range of applications. They have been used as refractories, abra…
The condition known as color blindness is a defect in vision that causes problems in distinguishing between certain colors. The condition is usually passed on genetically, and is more common in men than in women. About 6% of all men and about 0.6% of women inherit the condition. Individuals can also acquire the condition through various eye diseases. There is no treatment for color blindness. …
The Cerenkov effect is the emission of light from a transparent substance like water or glass when a charged particle, such as an electron, travels through the material with a speed faster than the speed of light in that material. The Cerenkov effect was discovered by Russian experimentalist P. A. Cerenkov in 1934 and explained by Russian theorists I. Y. Tamm and I. M. Frank. All three scientists …
A colugo is a furry mammal with a thin neck, a slender body, and large eyes. It is about the size of an average house cat, measuring between 15-16.5 in (38-42 cm) long with a tail adding another 8-10 in (20-25 cm). Also known as a flying lemur, the colugo neither truly flies nor is it a lemur. A gliding mammal, it is able to give the appearance of flight with the help of a membrane that stretches …
Earth's atmosphere is composed of about 78% nitrogen, 21% oxygen, and 0.93% argon. The remainder, less than 0.1%, contains many small but important trace gases, including water vapor, carbon dioxide, and ozone. All of these trace gases have important effects on the earth's climate. The atmosphere can be divided into vertical layers determined by the way temperature changes with heigh…
Modern biologists believe that life first appeared in the sea; from these marine beginnings, land-dwelling organisms such as mammals gradually evolved. Cetaceans have returned to the marine environment after an ancestral period on land. As evidence of their terrestrial pedigree, consider that a whale fetus possesses four limb buds, a pelvis, tail, and forelimbs with five fingers like any land mamm…
Chachalacas, curassows, and guans are 42 species of birds that make up the family Cracidae. These birds are in the order Galliformes, which also includes the grouse, pheasants, quail, guinea fowl, and turkey. Curassows, chachalacas, and guans (or cracids) are believed to represent a relatively ancient and primitive lineage within this order. Fossil members of this family are known from deposits in…
Coma, from the Greek word koma, meaning deep sleep, is a state of extreme unresponsiveness in which an individual exhibits no voluntary movement or behavior. In a deep coma, stimuli, even painful stimuli, are unable to effect any response. Normal reflexes may be lost. Coma lies on a spectrum with other alterations in consciousness. The level of consciousness which you, the reader, are currently en…
Chameleons are small, strange-looking lizards in the family Chamaeleonidae. There are 86 species of chameleons, in four genera. The majority of species of A chameleon catching an insect with its tongue. JLM Visuals. Reproduced by permission. chameleon are found in the tropics of Africa and Madagascar, but some species live in southern Spain, Crete, India, and Sri Lanka. Most species of cham…
Chaos theory is used to model the overall behavior of complex systems. Despite its name, chaos theory is used to identify order in complex and otherwise seemingly unpredictable systems. Chaos theory is used to understand explosions, complex chemical reactions (e.g., the Belousov-Zhabotinsky oscillating reaction that yields a red solution that turns blue at varying intervals of time), and many biol…
Combinatorics is the study of combining objects by various rules to create new arrangements of objects. The objects can be anything from points and numbers to apples and oranges. Combinatorics, like algebra, numerical analysis and topology, is a important branch of mathematics. Examples of combinatorial questions are whether we can make a certain arrangement, how many arrangements can be made, and…
There are many forms of evidence for evolution. One of the strongest forms of evidence is comparative anatomy; comparing structural similarities of organisms to determine their evolutionary relationships. Organisms with similar anatomical features are assumed to be relatively closely related evolutionarily, and they are assumed to share a common ancestor. As a result of the study of evolutionary r…
Charge-coupled devices (CCDs) have made possible a revolution in image processing. They consist of a series of light-sensitive elements, called pixels, arranged in a square or rectangular array. When CCDs are exposed to light, an image of the object being observed is formed; this image can be extracted from the CCD and stored on a computer for later analysis. CCDs are used in a variety of modern i…
A chemical element is a substance made up of only one kind of atom (atoms having the same atomic number). A compound, on the other hand, is made up of two or more kinds of atom combined together in specific proportions. The atomic number of an element is the number of protons found in the nucleus of each atom of that element; the number of protons in the nucleus equals the number of electrons that…
A chelate is a type of coordination compound in which a single metallic ion is attached by coordinate covalent bonds to a molecule or an ion called a ligand. The term chelate comes from the Greek word chela, meaning "crab's claw." The term clearly describes the appearance of many kinds of chelates, in which the ligand surrounds the central atom in a way that can be compared to…
Combustion is the chemical term for a process known more commonly as burning. It is certainly one of the earliest chemical changes noted by humans, at least partly because of the dramatic effects it has on materials. Today, the mechanism by which combustion takes place is well understood and is more correctly defined as a form of oxidation that occurs so rapidly that noticeable heat and light are …
In the spring of 1997, the night sky provided a spectacular light show as Comet Hale-Bopp, one of the brightest comets of the century, traversed the heavens. The comet was more closely studied than any before it, and scientists continue to make discoveries based on the data gathered by terrestrial and orbital telescopes and instrumentation. Originating primarily from the Oort Cloud, a belt of stel…
While anatomy is the study of the structures of an organism, physiology is the science dealing with the study of the function of an organism's component structures. However, it often is not enough to know what an organ, tissue, or other structure does. Physiologists want to know how something functions. For example, physiological questions might ask: What is the function of human lung tissu…
A comet is an object with a dark, solid core (the nucleus) some miles in diameter. The core is composed mostly of water ice and frozen gas and is surrounded—whenever the comet is close enough to the Sun for part of the core to vaporize—by a cloud of glowing vapor (the coma). Together, the core and coma comprise the comet's head, which appears as a bright, well-defined cloud. A…
A chemical bond is any force of attraction that holds two atoms or ions together. In most cases, that force of attraction is between one or more electrons held by one of the atoms and the positively charged nucleus of the second atom. Chemical bonds vary widely in their stability, ranging from relatively strong covalent bonds to very weak hydrogen bonds. …
Commensalism is a type of symbiosis, specifically, a biological relationship in which one species benefits from an interaction, while the host species is neither positively or negatively affected to any tangible degree. For example, epiphytic plants (which grow on other plants but are not parasitic) gain an enormous ecological benefit from living on larger plants, because they gain access to a sub…
Within the science of ecology, a community is a set of organisms coexisting within a defined area. Community ecology, then, is the study of the interactions that occur among groups of species coexisting within a region. For example, a community ecologist might consider the ways in which plants and animals within a forest affect one another's growth. Contrary to popular usage, the term ecolo…
Chemical evolution describes chemical changes on the primitive Earth that gave rise to the first forms of life. The first living things on Earth were prokaryotes with a type of cell similar to present-day bacteria. Prokaryote fossils have been found in 3.4-million-year-old rock in the southern part of Africa, and in even older rocks in Australia, including some that appear to be photosynthetic. Al…
"Commutativity" is a property an operation between two numbers (or other mathematical elements) may or may not have. The operation is commutative if it does not matter which element is named first. For example, because addition is commutative, 5 + 7 has the same value as 7 + 5. Subtraction, on the other hand, is not commutative, and the difference 5 - 7 does not have the same value a…
Chemical oxygen demand is related to biochemical oxygen demand (BOD), another standard test for assaying the oxygen-demanding strength of waste waters. However, biochemicaloxygen demand only measures the amount of oxygen consumed by microbial oxidation and is most relevant to waters rich in organic matter. It is important to understand that COD and BOD do not necessarily measure the same types of …
Chemical reactions describe the changes between reactants (the initial substances that enter into the reaction) and products (the final substances that are present at the end of the reaction). Describing interactions among chemical species, chemical reactions involve a rearrangement of the atoms in reactants to form products with new structures in such a way as to conserve atoms. Chemical equation…
In 1978, Philips and Sony together launched an effort to produce an audio compact disc (CD) as a method of delivering digital sound and music to consumers. The two companies continued to cooperate through the 1980s and eventually worked out standards for using the CD technology to store computer data. These recommendations evolved into the CD-ROM technology of today. The CD-ROM (compact disc-read …
Chemical warfare involves the use of natural or synthetic substances to incapacitate or kill an enemy or to deny them the use of resources such as agricultural products or screening foliage. The effects of the chemicals may last only a short time, or they may result in permanent damage and death. Most of the chemicals used are known to be toxic to humans or plant life. Other normally benign (mild)…
Chemistry is the science that studies why materials have their characteristic properties, how these particular qualities relate to their simplest structure, and how these properties can be modified or changed. The term chemistry is derived from the word alchemist, which finds its roots in the Arabic name for Egypt al-Kimia. The Egyptians are credited with being the first to study chemistry. They d…
Competition is a biological interaction among organisms of the same or different species associated with the need for a common resource that occurs in a limited supply relative to demand. In other words, competition occurs when the capability of the environment to supply resources is smaller than the potential biological requirement so that organisms interfere with each other. Plants, for example,…
Chemoreception is the biological recognition of chemical stimuli, by which living organisms collect information about the chemistry of their internal and external environments. Chemoreception has three sequential stages: detection, amplification, and signaling. In detection, a molecule typically binds to a chemoreceptor protein on the surface of a cell, changing the shape of the chemoreceptor. All…
Complementary deoxyribonucleic acid (DNA) is DNA in which the sequence of the constituent molecules on one strand of the double stranded structure chemically matches the sequence on the other strand. A useful analog is to picture a key and a lock. While there are many different types of keys, only one design matches the contours of the lock and so will fit into the lock. The different chemical mol…
A complex is a species in which the central atom is surrounded by a group of Lewis bases that have covalent bonds to the central atom. The Lewis bases that surround the central atom are generally referred to as ligands. Complexes are so named because when they were first studied, they seemed unusual and difficult to understand. Primarily, transition metals form complexes and their most observable …
From the Latin casūs (cases), casuistry is a method of practical reasoning that aims to identify the scope and force of moral obligations in the varied contexts of human action. While the golden era of casuistry belongs to the period 1450–1660, its origins as an intellectual outlook on moral decision-making can be traced back to ancient philosophy and to the legal traditions of mediev…
The causality debate has been centered on two issues, one metaphysical, the other epistemic. The metaphysical issue concerns the nature of the connection between cause and effect: How and in virtue of what does the cause bring about the effect? The epistemic issue concerns the possibility of causal knowledge: How, if at all, can causal knowledge be obtained? …
Chestnuts are species of trees in the genus Castanea, family Fagaceae. They are species of temperate hardwood (angiosperm-dominated) forests found in the Northern Hemisphere and are indigenous to eastern North America and Eurasia. Species in the genus Castanea can grow to be 100 ft (30 m) tall. They have simple leaves with a broadly toothed margin and sweet-smelling, yellowish, insect-pollinated, …
Philosophers have theorized about causation since well before Aristotle, who distinguished several types of causation: efficient, material, final, and formal. For example, a wood carving is made by an artist (the efficient cause) by chiseling a piece of wood (the material cause) for the purpose of creating a beautiful object (the final cause), arriving at something that has the properties of a woo…
A chi-square analysis is best illustrated using an example in which data from a population is categorized with respect to two qualitative variables. Table 1 shows a sample of patients categorized with respect to two qualitative variables, namely, congenital heart defect (CHD; present or absent) and karyotype (trisomy 21, also called Down syndrome, or trisomy 13, also called Patau syndrome). The cl…
Causation is defined most commonly as a relationship between two events or two states of affairs in which the first brings about the second. The idea of causation has long existed among the peoples in South and East Asia, but as a historical notion, it has taken different forms of expression in these regions. …
Typical complex numbers are 3 - i, 1/2 + 7i, and -6 - 2i. If one writes the real number 17 as 17 + 0i and the imaginary number -2.5i as 0 - 2.5i, they too can be considered complex numbers. Complex numbers are so called because they are made up of two parts which cannot be combined. Even though the parts are joined by a plus sign, the addition cannot be performed. The expression must be left as an…
Censorship comprises many methods of preventing the publication or dissemination of speech, printed matter, art, theater, music, electronic media, or other forms of expression. The most common subjects that are censored are religion, politics, and sex. The usual justification is that such expression is subversive, blasphemous, heretical, obscene, pornographic, or otherwise offensive or harmful. Ce…
"Cold things warm up, the hot cools off, wet becomes dry, dry becomes wet," observes Heracleitus (fr. 126), as if to state an obvious fact. Yet this fact became highly troublesome to early philosophers. …
The word character, when applied to persons, has two sources, distinguished lexically in ancient Greek by the terms êthos and charaktêr. Êthos, originally referring to a disposition or custom, from Aristotle on refers to the stable dispositions that guide a person's actions and that are suitable objects of moral praise and blame. The earliest uses of charactêr in Greek, …
Where and when did chemistry originate? Some chemists would identify ancient Egypt as the birthplace of chemistry because of that culture's glassworks, cosmetics, and mummification techniques. Advocates of this theory might also refer to a possible etymology of the word chemistry from the Egyptian word for black. Other historians place the origins of chemistry amid ancient Greek theories of…
Between 1966 and 1977, members of the Mexican-American community engaged in a period of widespread political activism akin to other civil rights and antiwar movements of the 1960s. The resulting challenges and concurrent mentalities became the Chicano movement, or as it is now known in recognition of the equally important participation of Chicanas, the Chicana/o movement. During this period large-…
Chickenpox, a disease characterized by skin lesions and low-grade fever, is common in the United States and other countries located in areas with temperate climates. The incidence of chickenpox is extremely high-almost everyone living in the United States contracts chicken-pox, usually during childhood, but sometimes in adulthood. In the United States, about 3.9 million people a year contract chic…
During the last two centuries, even amid poverty and war, more children have had the opportunity for successful lives than ever before. The modern concern for child health, education, and well-being, however, emerged only after long millennia in which children's welfare was subordinated to the needs and goals of caretakers and communities—a pattern also encountered today in developin…
The composite or aster family (Asteraceae) is one of the largest families of plants, containing about 20,000 species, distributed among more than 1,000 genera, and occurring widely on all continents, except Antarctica. This family is commonly regarded by modern botanists as the most advanced of the plant families, because of the complex, highly evolved structure of its multi-flowered, composite re…
Chinese thought is a generic term, referring to the ideas produced, expanded, and transmitted in the history of China. First, these ideas are not simply general opinions, but the philosophical views of the world, life, and society that have been commonly accepted as concepts or systematic theories. These ideas or theories are the end-products of logical reasoning—in Chinese, the two charact…
The term junfa became part of the Chinese vocabulary in the 1910s and gained popularity in the 1920s to describe the phenomenon of militarism that dominated the Chinese political scene between 1916 and 1928. While both characters, jun (military) and fa (as in menfa, prominent lineage), are ancient Chinese words, it was in Japan that fa as a suffix was paired with other words to mean "a cliq…
According to the writers of the Gospels, Jesus of Nazareth gathered a small group of disciples and went about for three years in first century Galilee, preaching a message of hope to the poor and healing the sick. John the "Baptist" had gone before him, calling people to repent and be baptized, promising the imminent coming of the Kingdom of Heaven. He recognized in Jesus a far great…
Since the 1970s, the study of Christianity in Asia has been transformed by new approaches in which the scholarly perspective has become less Eurocentric and more Asian. Particularly in regard to China, Western missionary sources have given way to Chinese sources while the meaning of Christianity has been broadened beyond a narrow religious content to include Asian cultural elements. The history of…
Diseases that are more common among children than among adults are referred to as childhood diseases. That is not to say that adults cannot or will not contract these illnesses; but usually children contract these diseases and form the immunity against them that will protect them as adults. In fact, some of these diseases may be quite uncomplicated in children, but may be life-threatening when con…
The latter half of the twentieth century witnessed a swift decline in the popularity and significance of cinemagoing in the West, associated with suburbanization and the rise of competitor media like rock and roll and television. From the 1990s, cinema release was repositioned as a cornerstone of multimedia-themed product lines, including alternative forms of distribution and exhibition (in-flight…
The chimaeras (order Chimaerae, class Bradyodonti) are a most peculiar looking group of fish that live near the sea bed off continental shelves and in deep offshore waters at a depth of 985-1,640 mi (300-500 m). Collectively these species form a small, cohesive group of about 25 species. They are all exclusively marine species. Closely related to sharks, rays, and dogfish, chimaeras are characteri…
Citizenship consists in sharing a political community, and enjoying the benefits and assuming the political responsibilities that give effect to this experience of shared political community. If the purpose of political philosophy is to provide a principled account of the nature and appropriate boundaries of political community, then it makes sense to say that the tradition of political philosophy…
A composite material is a microscopic or macroscopic combination of two or more distinct materials with a recognizable interface between them. For structural applications, the definition can be restricted to include those materials that consist of a reinforcing phase such as fibers or particles supported by a binder or matrix phase. Other features of composites include the following: (1) The distr…
From the early days of urbanization, several often competing conceptions of cities were evident: As a unit of analysis the city is often characterized through the emphasis on diversity, fragmentation, strangeness, encounters with strangers, the mosaic of variety, contingent interactions, moving borders, everyday life and events, and the multitude of interactions. However, another perspective focus…
In Western political thought, ideas about cities, citizenship, and democracy have always been inextricably linked. Since Socrates suggested in The Republic that his interlocutors help him to create a city in speech, the city has functioned as a real and metaphorical center for struggles over what it means to be political. Ideas about civilization and barbarism, egalitarianism and exclusion, virtue…
Islam first developed and spread in a region of the world where urban civilizations had originated. Caravan routes crisscrossed the Fertile Crescent and the Arabian peninsula several millennia prior to the birth of Christianity, linking the urban-centered civilizations of Mesopotamia, the Nile Valley, and the Indian subcontinent. Overland routes were supplemented by water transit via the Red Sea a…
The history of the city in Latin America stretches over three thousand years and a vast geographic area. The cities vary considerably over space and time. Prior to the coming of the Spaniards, many pre-Columbian cities are thought to have been cosmograms or cosmologically conceived—the cities' buildings and plans emulated the cosmos as their leaders conceived of it. After the conques…
Civil disobedience is an illegal act performed publicly in contravention of a law or laws of the government for the short-term purpose of bringing about a change in the law or laws and for the long-term purpose of improving society as a whole. It is a political act because its underlying principles are the principles of political justice that regulate the state and its institutions, and not those …
An ancient term of Western political and social theory, civil society has enjoyed enormous popularity in recent years and has outstripped its geographic origins to spread all over the world. Public leaders, newspaper writers, religious figures, social theorists, political activists, and commentators from many different perspectives now use the term on a regular basis. The term's meaning has…
Stream valleys, channels, and floodplains form complicated systems that evolve through time in response to changes in sediment supply, precipitation, land use, and rates of tectonic uplift affecting a drainage basin. Stream channels serve to convey flow during normal periods, whereas floodplains accommodate flow above the bankfull stage (floods) that occurs with frequencies inversely proportional …
"All vogue words tend to share a similar fate," observes Zygmunt Bauman. "The more experiences they pretend to make apparent, the more they themselves become opaque. The more numerous are the orthodox truths they elbow out and supplant, the faster they turn into no-questions-asked canons" (p. 1). Bauman's specific subject was globalization, but he may well have b…
Composting is the process of arranging and manipulating organic wastes so that they are gradually broken down, or decomposed, by soil microorganisms and animals. The resulting product is a black, earthy-smelling, nutritious, crumbly mixture called compost or humus. Compost is usually mixed with other soil to improve the soil's structural quality and to add nutrients for plant growth. Compos…
The Latin genesis of class nomenclature does not mean that the idea behind it (in either a social or general sense) did not exist prior to the rise of the Roman Republic. Aristotle's Organon proposed a logical system of classification of natural and linguistic types into genus and species according to categorical criteria. For the ancient Greeks, the Few and the Many constituted a central m…
Chimpanzees belong to the order Primates, which includes monkeys, apes, and humans. Chimpanzees are assigned to the family Pongidae, which includes all of the other apes: gorillas, orang-utans, and gibbons. Compared with monkeys, apes are larger, have no tail, and have longer arms and a broader chest. When apes stand upright, their long arms reach below their knees. They also have a great deal of …
The next neoclassical period, which we call the Renaissance, exploded in Italy under the patronage of such personages as the Medicis and Pope Leo X. The Renaissance with its focus on secular life, fortified by the availability of the important literary works of the Romans and by translations of the Greeks into Latin, sometimes via Arabic, and then by the study of Greek, enabling educated people to…
Chinchillas and viscachas are seven species of small, South American rodents in the family Chinchillidae. Chinchillas have a large head, broad snout, large eyes, rounded ears, and an extremely fine and dense fur. Their forelimbs are short and the paws small, while the hindlegs and feet are larger and relatively powerful, and are used for a leaping style of locomotion, as well as for running and cr…
The concept of classification seems obvious and benign. To classify is to arrange or distribute according to a system or method, a sense of the word that has not altered since its inception in antiquity. The significance of classification lies not in what it means, but in how it is applied. How people classify—according to what principles—has evolved and altered over time as their un…
Chipmunks are small mammals in the order Rodentia, the rodents. Specifically, they are classified with the squirrel-like rodents, the Sciuridae. Chipmunks are divided into two genera: Gallos and Tamias. North America is home to 17 species of chipmunk, 16 in the West and only one, Tamias striatus, the eastern chipmunk, in the East. The eastern chipmunk is about 5-6 in (12.7-15 cm) long, and the tai…
Conceptions and characterizations of colonialism vary considerably among scholars of Africa. Differences and debates center on four sets of interrelated issues: first, the place and importance of the colonial period in African history; second, the nature of the colonial encounter and its driving force; third, the typologies of African colonialism; and fourth, the legacies of colonialism for postco…
Chitons are small mollusks, oval in outline, with a broad foot, and a mantle that secretes, and sometimes extends over, the shell. They live on rocky seashores in much the same life-style as limpets. They are easily distinguishable from limpets, however, by their shell made of eight plates (or valves) with transverse sutures. Also, unlike limpets and other snails, the chitons have no tentacles or …
Colonialism is all about the exercise of power and its consequences. Theoretically, the exercise of power entails the interaction of at least two parties negotiating (by various means or practices) their wills on one or more issues, as shown by their various actions or statements. This definition holds for interactions of both individuals and institutions. The imposition of one state's will…
Chlordane is an organochlorine insecticide, more specifically a chlorinated cyclic hydrocarbon within the cyclodiene group. The proper scientific name for chlordane is 1,2,4,5,6,7,8,8-Octachloro-3a,4,7,7a-tetrahydro-4,7-methanoindan. However, the actual technical product is a mixture of various chlorinated hydrocarbons, including isomers of chlordane and other closely related compounds. The first …
Studies detailing the nature of colonial policy and practice in Southeast Asia have all acknowledged its disparate nature and overwhelming range of characteristics. While many European powers shared the desire to establish colonies overseas, the manner in which this was accomplished was more random than regular. Factors contributing to this variance include differing philosophies of administrative…
A compound is a substance composed of two or more elements chemically combined with each other. Historically, the distinction between compounds and mixtures was often unclear. Today, however, the two can be distinguished from each other on the basis of three primary criteria. First, compounds have constant and definite compositions, while mixtures may exist in virtually any proportion. A sample of…
The common-sense philosophers of the Scottish school—including Thomas Reid, Dugald Stewart, James Beattie, George Campbell, and James Oswald—argued against George Berkeley and David Hume that ordinary human perception and moral judgment need not be defended against skeptical inquiry but ought to be taken as self-evident. As Campbell put it, "to maintain propositions the revers…
The Compton effect (sometimes called Compton scattering) occurs when an x ray collides with an electron. In 1923, Arthur H. Compton did experiments bouncing x rays off the electrons in graphite atoms. Compton found the x rays that scattered off the electrons had a lower frequency (and longer wavelength) than they had before striking the electrons. The amount the frequency changes depends on the sc…
The communication of ideas in and from Africa is characterized by enormous changes over time and variations among societies. Historically, as might be expected for such a large and ancient continent—the second largest in the world and the one where humanity originated—African societies have exhibited high levels of cultural diversity, uneven patterns of political and socioeconomic de…
Anthropological research suggests a rich and historically deep tradition of oral communication among early Amerindian people in which linguistic diversity appears to have been considerable. Even within the usually accepted language groupings of North America—Eskimo-Aleut; Athabascan, or Na-Dene; Algonquian-Wakashan; Aztec-Tanoan; Hokan-Siouan; Penutian; and Arawakan—many dialects exi…
Asia comprises a vast amount of land divided into numerous countries, many of which have civilizations dating back thousands of years. Due to the huge scope of this topic, this entry will focus on India as an important hub for the transmission of ideas throughout Asia and how other Asian countries influenced the development of Indian civilization. When India became independent in 1947, the new gov…
Homer's Iliad and Odyssey occupy an important early niche in the history of European literature. It has been argued, however, that the Homeric epics, strictly speaking, are not even literature. In An Essay of the Original Genius and Writings of Homer (1775), the English diplomat and archaeologist Robert Wood initiated a continuing debate by arguing that Homer could not read or write and tha…
The main concern of psychiatrists and therapists who treat people with compulsions is the role they play in a mental illness called obsessive-compulsive disorder (OCD). Compulsions need to be distinguished from obsessions in order to understand how they interconnect with compulsive behavior and reinforce this debilitating illness. In psychiatric literature, compulsions are defined as repetitive be…
The great continental Eurasian landmass, with its vast steppes stretching east to west in a more or less uniform climatic belt, has been a useful path for the transit of ideas and techniques throughout history, with what is now the Arab world as the fulcrum of the exchange between China and Europe. Over roughly the first thirteen or fourteen centuries of the Common Era, there was a slow, steady di…
A very large and diverse group of organic molecules are chlorinated hydrocarbons. Hydrocarbons are molecules composed entirely of hydrogen and carbon atoms, often derived from carbon-based fossil fuels like petroleum oils and coal. Chlorinated hydrocarbons are specific hydrocarbon molecules that also have atoms of the element chlorine chemically bonded to them. The number of chlorine atoms bonded …
The communication of ideas is not basically different from any other type of human communication. It is founded on the unique human skill of speech, a highly developed and formalized system of audio communication, which links with animal sounds and other forms of the communicative act but is infinitely more sophisticated. The jury is still out on the question of the genetic component in spoken lan…
Chlorination is the process by which the element chlorine reacts with some other substance. Chlorination is a very important chemical reaction both in pure research and in the preparation of commercially important chemical products. For example, the reaction between chlorine and methane gas produces one or more chlorinated derivatives, the best known of which are trichloromethane (chloroform) and …
The Lao-Thai culture area, encompassing modern Thailand, Laos, Cambodia, and Burma (present-day Myanmar), has a common history of Hinduized states and Theravada Buddhism. Pali (the language of early Buddhist texts) and Sanskrit (the language of early Hinduism) are also Indian in origin. Vietnam, while sharing aspects of mainland Southeast Asian culture and society, represents the cultural influenc…
"A spectre is haunting Europe—the spectre of Communism." The famous opening line to The Communist Manifesto evokes the expectations and fears that have been associated with European communism. Published in 1848 amid a tumultuous period of political unrest across the continent, this polemical pamphlet was an idealistic call to arms directed at an emerging male working class (&#…
Latin America in the 1890s was a society primed for the dissemination of socialist ideologies. It was ruled by autocrats and oligarchs who were exploiting an increasingly discontented peasant populace and perpetuating a sharply divided two-class social structure. During this time, increased productivity and foreign investment ushered in the earlier stages of exploitative capitalism as well as a wa…
This essay explores representative Africanist thought on personhood and community, highlighting especially the debate between Ifeanyi Menkiti and Kwame Gyekye on communitarianism, defined generally as relating to social organization in small, cooperative, partially collectivist communities. The general debate on these issues in Africa can be traced to important studies of personhood and psychology…
Chlorine is the non-metallic chemical element of atomic number 17, symbol Cl, atomic weight 35.45, melting point -149.8°F (-101°C), and boiling point -29.02°F (-33.9°C). It consists of two stable isotopes, of mass numbers 35 and 37. Ordinary chlorine is a mixture of 75.77% chlorine-35 atoms and 24.23% chlorine-37 atoms. Chlorine is a highly poisonous, greenish yellow ga…
The nucleus is a large membrane-bound cell organelle which houses the chromosomes and which occupies roughly 10% of the volume of all eukaryotic cells. The nucleus is separated from the rest of the cell and the cytoplasm by a double membrane known as the nuclear envelope. The outer layer of the nuclear membrane is studded with small openings called nuclear pores, which allow for the controlled mov…
A computer language is the means by which instructions and data are transmitted to computers. Put another way, computer languages are the interface between a computer and a human being. There are various computer languages, each with differing complexities. For example, the information that is understandable to a computer is expressed as zeros and ones (i.e., binary language). However, binary lang…
The field called computer science was born in the 1940s, though its roots extend back to the nineteenth century and even earlier. One of the early founders of the field was Alan Turing (1912–1954), a citizen of Great Britain, who in 1937 published his famous paper entitled "On Computable Numbers with an Application to the Entscheidungsproblem." In this paper he introduced the …
The concepts the learners used were appropriated from the pre-Confucian discourse of a broad class of warriors across the North China Plain. In this discourse power and virtue ideally were one (de). The worlds of men and of spirits (gui or shen) were separate but communication between the two was possible, and so was mutual intervention. Shamans and oracles were the agents of communication, while …
Consciousness has three distinct meanings in the modern world. First it refers to immediate subjective experience. Second, it is the source of immediate and certain knowledge of mental states. For example, if I am in pain, I am conscious of pain and certain of this knowledge of my mental state. Third, it is self-consciousness, a concept of the self that answers the question "Who am I"…
Human consciousness in Chinese thought may be seen in three layers, each of which requires the other two for both development and understanding. While these three layers of consciousness are constructed for analytical purposes, in reality they are interconnected. Psychologically, they represent different frames of reference, but they are also different dimensions of the same individual and/or coll…
Chlorofluorocarbons (CFCs) are man-made chemical compounds used as refrigerants, cleaning solvents, aerosol propellants, and blowing agents for foam packaging in many commercial applications. CFCs do not spontaneously occur in nature. They were developed by industrial chemists searching for a safer alternative to refrigerants used until the late 1920s. CFCs are non-toxic, chemically non-reactive, …
There is enormous diversity among the various traditions of classical Indian philosophy concerning the nature of consciousness and the place of humanity in the cosmos, but there are a number of presuppositions that are shared by many of India's great thinkers. Most classical Indian philosophical schools agree, for example, that living beings are reborn over and over again in a beginningless…
Chloroform was originally used to calm people suffering from asthma. In 1847, James Y. Simpson, a Professor of Midwifery at the University of Edinburgh, began using chloroform as an anesthetic to reduce pain during childbirth. From this initial experiment, chloroform began to be used as general anesthesia in medical procedures throughout the world. The use of chloroform in this application was eve…
Conservatism lends itself to misunderstanding because its political designation is easily confused with popular usage. To be conservative in the sense of preferring the familiar to the unfamiliar is a common form of behavior. Since this attitude toward life is universal, it issues from no necessary political commitment. For any person, even the most bohemian, not to develop a settled habit or a li…
Chlorophyll is a green pigment contained in the foliage of plants, giving them their notable coloration. This pigment is responsible for absorbing sunlight required for the production of sugar molecules, and ultimately of all biochemicals, in the plant. Chlorophyll is found in the thylakoid sacs of the chloroplast. The chloroplast is a specialized part of the cell that functions as an organelle. O…
Computers are built of electronic components encased in a sturdy metal container and attached to the outside of the container. Examples of hardware include electrical connections, circuit boards, hard and disk drives, viewing monitor, and printer. The components and the container are referred to as hardware. On their own, computer hardware is functionally useless. For the electronic circuitry to b…
"Consilience of inductions" is a phrase that was invented by the nineteenth-century English historian and philosopher of science William Whewell (1794–1866; pronounced "Hule"), and introduced in his Philosophy of the Inductive Sciences (1840). Whewell was trying to capture the notion of what Isaac Newton (1642–1727) had labeled a "true cause,"…
Chloroplasts are organelles—specialized parts of a cell that function in an organ—like fashion. They are found in vascular plants, mosses, liverworts, and algae. Chloroplast organelles are responsible for photosynthesis, the process by which sunlight is absorbed and converted into fixed chemical energy in the form of simple sugars synthesized from carbon dioxide and water. Chloroplas…
A computer virus is a program or segment of executable computer code that is designed to reproduce itself in computer memory and, sometimes, to damage data. Viruses are generally short programs; they may either stand-alone or be embedded in larger bodies of code. The term "virus" is applied to such code by analogy to biological viruses, microorganisms that force larger cells to manuf…
Constitutionalism is commonplace in modern political discourse in the West and beyond, yet it remains an elusive concept. Some have considered it impossible (and unnecessary) to give a definition of it. Nonetheless, one can discern several common features of the concept: the rule of law, not of men; limitations of political authority; the protection of civic rights and liberties; and rule based on…
Computerized axial tomography (CAT) is a diagnostic procedure that employs x rays in a unique manner. The CAT scan machine is computer controlled to assure accuracy in placement of the x-ray beam. Axial refers to the fact that the x-ray tubes are arranged in an arc about an axis. Tomography is a combination of tomo, from the Greek meaning "to cut," and graph, "to draw,"…
Consumerism, the central economic and social policy of contemporary capitalism, is a doctrine of growing the economy through constantly increasing the consumption of commodities and services. The term consumerism is also used to describe movements to protect the rights and interests of consumers. …
Concentration is a ratio of how much of one ingredient is present in a mixture, compared to the whole mixture or compared to the main ingredient, often the solvent. The amounts of each substance can be expressed in mass or volume units, and many different units can be used. The components of the mixture can be gases, liquids, or solids. Earth's atmosphere, for example, is a mixture of gases…
It was in the sixteenth and seventeenth centuries, especially in Italian, French, English, and German, that the term "context" (contesto, contexture, Kontext) began to be used with frequency. From the sentences before and after the passage to be interpreted, "context" came to refer to the coherence of a text, the relation of the parts and the whole. The term was also ex…
Concrete, from the Latin word concretus meaning "having grown together," generally consists of Portland cement, water, and a relatively unreactive filler called aggregate. The filler is usually a conglomerate of gravel, sand, and blast-furnace stony matter known as slag. When Portland cement is mixed with water, the various ingredients begin to react chemically with the water. For a …
The term continental philosophy was coined by English-speaking analytic philosophers in Great Britain and the United States shortly after World War II. Since then, the term has been used primarily by English-speaking philosophers but not by western European philosophers, who see no need to call themselves "continental." The differences between analytic and continental philosophy are …
Consider the first sentence of Jean-Jacques Rousseau's (1712–1778) Discours sur les arts et sciences (Discourse on the arts and sciences, 1750): "Has the restoration of the sciences and arts contributed to the purification of mores, or their corruption?" Corruption denotes deterioration, a qualitative decline from an original (absolutely or relatively) natural or pristi…
Cholera is one of the most devastating of all human diseases. Although endemic in some areas of the world, cholera is usually associated with massive migrations of people, such as those occurring during war or famine. Cholera is also common in developing countries, where suboptimal sanitation practices are responsible for its spread. If not treated, cholera has a fatality rate of over 60%. Death r…
While corruption, in one form or another, has perverted virtually all human societies throughout history, it has not had uniform impact on any one of them. Scholars who study corruption in an effort to find ways to minimize it have had to deal with the fact that it is difficult to define and measure, making empirical testing very difficult. …
While the Upanishads mark the end of the Vedas, the cosmologies introduced there continue to be developed in the subsequent texts (for example, the Manava Dharmashastra or Manusmriti [Laws of Manu], the Vishnu Purana, and sections of the Mahabharata). While these texts differ somewhat in content, they mutually inform what has come to be the prevailing cosmology in the Hindu tradition. This cosmolo…
Early cosmologies, or worldviews, envisioned a universe subject to the whims of gods and were anthropocentric: focused on the role and fate of human beings. As such, cosmology and religion were often intertwined. …
Conditioning is a term used in psychology to refer to two specific types of associative learning as well as to the operant and classical conditioning procedures which produce that learning. Very generally, operant conditioning involves administering or withholding reinforcements based on the performance of a targeted response, and classical conditioning involves pairing a stimulus that naturally e…
Cosmopolitanism refers to both a lifestyle incorporating aspects from all or many parts of the world and an ideology based upon the premise that every human shares, or should share, equal status as a "citizen of the world." The two are not exclusive of one another, but it is certainly possible to encounter either the ideal or the lifestyle without the presence of the other. Though si…
Cholesterol belongs more specifically to a class of compounds known as the steroids. Most steroids are naturally occurring compounds that play critical roles in plant and animal physiology and biochemistry. Other steroids include sex hormones, certain vitamins, and adrenocorticoid hormones. All steroids share a common structural unit, a four-ring structure known as the perhydrocyclopentanophenanth…
Condors are New World vultures that are among the largest of flying birds. There are only two species, the Andean condor (Vultur gryphus) and the critically endangered California condor (Gymnogyps californianus). They are related to the smaller vultures of the Americas, including the king vulture (Sarcoramphus papa) and turkey vulture (Cathartes aura), which also belong to family Cathartidae. In t…
Chordates are a diverse group of animals that comprise the phylum Chordata. There are approximately 44,000 species of chordates, ranging in size from several millimeters to 105 ft (32 m) long. The simplest and earliest chordates are pre-vertebrate animals such as ascidians, tunicates, and Amphioxus. The major group of chordates are the sub-phylum Vertebrata, the vertebrates. Listed more-or-less in…
The term congenital is used to describe a condition or defect that exists at birth. Congenital disorders are inborn. They are present in the developing fetus. Sickle cell disease, Down syndrome, and congenital rubella syndrome are three examples of congenital conditions in humans. Congenital disorders result from abnormalities in the fetus's genetic inheritance, conditions in the fetal envi…
Chorionic villus sampling (CVS) is a relatively new form of a prenatal testing, completed earlier in gestation than the more traditional testing method, amniocentesis. Through CVS, small samples of the trophoblast are obtained for chromosome or DNA analysis. The use of CVS as a tool for fetal karyotyping at 10 weeks' gestation was introduced in 1969 but it became accepted with the introduct…
Two triangles are congruent if they are alike in every geometric respect except, perhaps, one. That one possible exception is in the triangle's "handedness." There are only six parts of a triangle that can be seen and measured: the three angles and the three sides. The six features of a triangle are all involved with congruence. If triangle ABC is congruent to triangle DEF, th…
Chromatin is the masses of fine fibers comprising the chromosomes in the nucleus of a eukaryotic cell in a nondividing state. During cell division (mitosis or meiosis) the chromatin fibers pull together into thick shortened bodies which are then called chromosomes. Chromatin is present only in cells with a nuclear membrane; it is not found in prokaryotic cells (e.g., bacteria) that lack a nucleus.…
A conic section is the plane curve formed by the intersection of a plane and a right-circular, two-napped cone. Such a cone is shown in Figure 1. The cone is the surface formed by all the lines passing through a circle and a point. The point must lie on a line, called the "axis," which is perpendicular to the plane of the circle at the circle's center. The point is called the …
Conifer (common name for phylum Pinophyta) is a type of tree that thrives in temperate and boreal climates. Characterized by seed-bearing cones, conifers typically have narrow, needle-like leaves covered with a waxy cuticle, and straight trunks with horizontal branches. These trees are usually evergreen, meaning they do not shed their leaves all at once, and can photosynthesize continually. There …
Chromatography is a family of laboratory techniques for separating mixtures of chemicals into their individual compounds. The basic principle of chromatography is that different compounds will stick to a solid surface, or dissolve in a film of liquid, to different degrees. To understand chromatography, suppose that all the runners in a race have sticky shoe soles, and that some runners have sticki…
Connective tissue is found throughout the body and includes fat, cartilage, bone, and blood. The main functions of the different types of connective tissue include providing support, filling in spaces between organs, protecting organs, and aiding in the transport of materials around the body. Connective tissue is composed of living cells and protein fibers suspended in a gel-like material called m…
Conservation is the philosophy that natural resources should be used cautiously and rationally so that they will remain available for future generations of people. American conservationist thought has evolved from its inception in the mid 1850s, when naturalists, businesspeople and statesmen alike foresaw environmental, economic and social peril in the unregulated use and abuse of North America&#x…
Chromosome abnormalities describe alterations in the normal number of chromosomes or structural problems within the chromosomes themselves. Both kinds of chromosome abnormalities may result from an egg (ovum) or sperm cell with the incorrect number of chromosomes, or with a structurally faulty chromosome uniting with a normal egg or sperm during conception. Some chromosome abnormalities may occur …
Conservation laws refer to physical quantities that remain constant throughout the multitude of processes which occur in nature. If these physical quantities are carefully measured, and if all known sources are taken into account, they will always yield the same result. The validity of the conservation laws is tested through experiments. However, many of the conservation laws are suggested from th…
A constellation is a group of stars that form a long-recognized pattern in the sky. The names of many constellations are Greek in origin and are related to ancient mythology. The stars that make up a constellation may be at very different distances from the earth and from one another. The pattern is one that we as humans choose to see and has no physical significance. Novice stargazers are often t…
Cellular respiration is the process by which a living cell produces adenosine triphosphate (ATP), carbon dioxide, and water from oxygen and organic fuel. It is a catabolic pathway that involves the release of stored energy from the break down of complex molecules to more simple ones. No single chemical reaction covers the entire process of cellular respiration. Instead it is the cumulative functio…
Much of Euclidean geometry is based on two geometric constructions: the drawing of circles and the drawing of straight lines. To draw a circle with a compass, one needs to know the location of the center and some one point on the circle. To draw a line segment with a straightedge, one needs to know the location of its two end points. To extend a segment, one must know the location of it or a piece…
A chromosome is a threadlike structure found in the nucleus of most cells. that carries the genetic material in the form of a linear sequence of deoxyribonucleic acid (DNA). In prokaryotes, or cells without a nucleus, the chromosome represents circular DNA containing the entire genome. In eukaryotes, or cells with a distinct nucleus, chromosomes are much more complex in structure. The function of …
Chromosome mapping is the assignment of genes to specific locations on a chromosome. A gene map serves many important functions and is much like understanding the basic human anatomy to allow doctors to diagnose patients with disease. A doctor requires knowledge of where each organ is located as well as the function of this organ to understand disease. A map of the human genome will allow scientis…
The presence of toxic and radioactive chemicals in soil at concentrations above trace levels poses potential risks to human health and ecological integrity. Soil can be contaminated by many human actions, including discharge of solid or liquid materials to the soil surface, pesticide and fertilizer application, subsurface release from buried tanks, pipes, or landfills, and deposition of atmospheri…
Cicadas are insects in the order Homoptera, family Cicadidae. Male cicadas make a well-known, loud, strident, buzzing sound during the summer, so these unusual insects are often heard, but not necessarily seen. Species of cicadas are most diverse in closed and open forests of the temperate and tropical zones. …
Contamination generally refers to the occurrence of some substance in the environment. The contaminant may be present in a larger concentration than normally occurs in the ambient environment. However, contamination is only said to occur when the concentration is smaller than that at which measurable biological or ecological damage can be demonstrated. Contamination is different from pollution, wh…
A continent is a large land mass and its surrounding shallow continental shelf. Both are composed of felsic crust. Continents, as by-products of plate tectonic activity, have grown to cover about one-third of Earth's surface over the last four billion years. Continents are unique to Earth, as plate tectonics does not occur on the other planets of our solar system. Continent interiors consis…
The World Health Organization (WHO) has named tobacco one of the greatest public health threats of the twenty-first century. As of 2001, more than 1.2 billion people worldwide smoke, and 3.5 million people are expected to die from causes directly related to tobacco use. This death rate is expected to rise to 10 million by the year 2030. Seventy percent of these deaths will occur in developing coun…
The relative movement of the continents is explained by modern theories of plate tectonics. The relative movement of continents is explained by the movement Diagram illustrating formation of continental margins. (a) Materials in Earth's mantle move up (often through volcanos) expanding the continental crust and causing rifting. (b) As it divides, the continental crust thins, and contin…
Living things require a circulatory system to deliver food, oxygen, and other needed substances to all cells, and to take away waste products. Materials are transferred between individual cells and their internal environment through the cell membrane by diffusion, osmosis, and active transport. During diffusion and osmosis, molecules move from a higher concentration to a lower concentration. Durin…
The continental margin is that portion of the ocean that separates the continents from the deep ocean floor. For purposes of study, the continental margin is usually subdivided into three major sections: the continental shelf, the continental slope, and the continental rise. In addition to these sections, one of the most important features of the continental margin is the presence of very large su…
The terms circumscribed and inscribed refer, respectively, to geometric figures that have been drawn around the outside of or within some other geometric figure. For example, imagine that a circle is drawn around a triangle so that the circle passes through all three vertices of the triangle. Then the circle is said to be circumscribed around the triangle, and the triangle is said to be inscribed …
The continental shelf is a gently sloping and relatively flat extension of a continent that is covered by the oceans. Seaward, the shelf ends abruptly at the shelf break, the boundary that separates the shelf from the continental slope. The shelf occupies only 7% of the total ocean floor. The average slope of the shelf is about 10 ft per mi (1.9 m per km). That is, for every one kilometer of dista…
The continuity of space or time, considered by Zeno and others, is represented in mathematics by the continuity of points on a line. As late as the seventeenth century, mathematicians continued to believe, as the ancient Greeks had, that this continuity of points was a simple result of density, meaning that between any two points, no matter how close together, there is always another. This is true…
One of the earliest methods of conservation tillage came to be known as contour plowing, or "plowing on the contour." Tilling the soil along the gentle slopes of a piece Contour rice farming in Arkansas. Photograph by Paul Logsdon. Phototake NYC. Reproduced by permission. of cropland, instead of up and down the gradient, prevents fertile topsoil from being carried downhill by fl…
Cirrhosis is a degenerative liver disease in which the lobes of the liver become infiltrated with fat and fibrous tissue (fibrous tissue is a type of connective tissue composed of protein fibers called collagen). The word "cir rhosis" is derived from the Greek words kirrhos, meaning "yellowish orange" and osis, meaning "condition," and connotates the appea…
Citric acid is an organic (carbon based) acid found in nearly all citrus fruits, particularly lemons, limes, and grapefruits. It is widely used as a flavoring agent, preservative, and cleaning agent. The structure of citric acid is shown below. The COOH group is a carboxylic acid group, so citric acid is a tricarboxylic acid, possessing three of these groups. Citric acid helps to provide the �…
Citrus trees are various species of trees in the genus Citrus, in the rue family, or Rutaceae. There are 60 species in the genus Citrus, of which about 10 are used in agriculture. The center of origin of most species of Citrus is southern and southeastern Asia. Citrus trees are widely cultivated for their edible fruits in sub-tropical and tropical countries around the world. The sweet orange (Citr…
In the United States, about 64% of women between 15 and 44 years of age used contraception in 1995, a total of about 60 million. Worldwide, contraceptive use increased 10-fold from 1963 to 1993. However, contraception remains controversial, with some religious and political groups opposed to the distribution of contraceptives. …
Small to medium-sized carnivores, civets are in the Viverridae family which includes genets, linsangs, and mongooses. There are 35 species of civets and genets in 20 genera. Their natural distribution is restricted to the warmer regions of the Old World, and they occupy a niche similarly filled by weasels and their relatives found in temperate deciduous forests. Civets vary in size and form, but m…
Convection is the vertical transfer of mass, heat, or other properties in a fluid or substance that undergoes fluid-like dynamics. Convection takes place in the atmosphere, in the oceans, and in Earth's molten subcrustal asthenosphere. Convective currents of air in the atmosphere are referred to as updrafts and downdrafts. In addition to heat transfer, convention can be driven by other prop…
Climax is a theoretical, ecological notion intended to describe a relatively stable community that is in equilibrium with environmental conditions, and occurring as the terminal, end-point of succession. One of the early proponents of the concept of climax was the American ecologist, Frederic Clements. In an important publication in 1916, he theorized that there was only one true climax community …
A coordination compound is formed when groups of atoms, ions, or molecules chemically bond with each other by donating and accepting pairs of electrons. Groups donating electron pairs are called ligands. They are usually Lewis bases. Groups accepting electron pairs are often transition metal cations. Figure 1. Formation and representations of a coordinate-covalent bond. Illustration by Ha…
Clingfish are about 100 species of small, ray-finned bony fish found primarily in tropical marine waters. They belong to the family Gobiesocidae in the order Gobiesociformes. Clingfish are shaped like tadpoles with a wide, flattened head; they have no scales and are covered with a thick coating of slime that makes them very slippery. Clingfish are characterized by a large suction disc formed by th…
Catabolism is the breakdown of large molecules into small molecules. Its opposite process is anabolism, the combination of small molecules into large molecules. These two cellular chemical reactions are together called metabolism. Cells use anabolic reactions to synthesize enzymes, hormones, sugars, and other molecules needed to sustain themselves, grow, and reproduce. Energy released from organic…
A clone is a molecule (DNA), cell, or organism that is genetically identical to its parental molecule, cell, or organism. There are three types of cloning. One method, gene cloning, utilizes copying fragments of DNA for easier manipulation and study. Another cloning method involves producing genetically identical animals through a process called twinning. The final cloning method involves producin…
Humans used the process known as catalysis long before, they understood what took place in that process. For example, soap-making, the fermentation of wine to vinegar, and the leavening of bread are all processes that involve catalysis. Ordinary people were using these procedures in their everyday lives without knowing that catalysis was involved. The term catalysis was proposed in 1835 by the Swe…
A closed curve is one which can be drawn without lifting the pencil from the paper and which ends at the point where it began. In Figure 1, A, B, and C are closed curves; D, E, and F are not. Curve A is a circle. Although the starting point is not indicated, any of its points can be chosen to serve that purpose. Curve B crosses itself and is therefore not a "simple" closed curve, but…
Catastrophism is the doctrine that Earth's history has been dominated by cataclysmic events rather than gradual processes acting over long periods of time. For example, a catastrophist might conclude that the Rocky Mountains were created in a single rapid event such as a great earthquake rather than by imperceptibly slow uplift and erosion. A new concept, uniformitarianism, grew from the wo…
"Closure" is a property which a set either has or lacks with respect to a given operation. A set is closed with respect to that operation if the operation can always be completed with elements in the set. For example, the set of even natural numbers, 2, 4, 6, 8,..., is closed with respect to addition because the sum of any two of them is another even natural number. It is not closed …
Copepods are pale or translucent crustaceans, measuring between 0.04 mm to several millimeters long. They have adapted to many different habitats; while they usually live in salt water, copepods can live in lakes and ponds as well. Furthermore, they have different modes of locomotion: some can swim purposefully but others are planktonic, floating with the current. Scientists generally A copep…
Catfish include some 2,500 species of mostly freshwater fish characterized by two to four pairs of whiskers or barbels around their mouth. Many species have spines on the dorsal fins and near the gills. In some species these spines may contain poison. Catfish belong to the bony fish order Siluriformes, and are mainly freshwater forms with representatives throughout the world. Most species of catfi…
Catheters are long, flexible tubes that are inserted into the body for various purposes, either to remove an unwanted substance or to instill nourishment or medication. A relatively large catheter can be passed through the nose, down the throat and into the stomach to remove the contents of the stomach; for example, if someone has consumed a poisonous substance, a catheter can be used to remove a …
The cathode is one of the two electrodes that are present in any system in which electricity is entering and leaving a region; the other electrode is called the anode. The electric current enters through one of the electrodes and leaves through the other. Two general kinds of systems employ electrodes: vacuum tubes (also called gas discharge tubes) and electrochemical cells. In a vacuum tube, the …
Copper is the metallic chemical element of atomic number 29, symbol Cu, atomic weight 63.55, specific gravity 8.96, melting point 1,985°F (1,085°C), and boiling point 4,645.4°F (2,563°C). It consists of two stable isotopes, of mass numbers 63 (69.1%) and 65 (30.9%). Copper is one of only two metals that are colored, Copper is reddish brown, while gold is...gold—a…
All clouds are a form of water. Clouds are condensed atmospheric moisture in the form of minute water droplets or ice crystals. The creation of a cloud begins at ground level. The sun heats the earth's surface, the warm ground heats the air, which rises. The air contains variable amounts of water, as vapor, that has evaporated from bodies of water and plants. Air at ground level is denser t…
A cathode ray tube is a device that uses a beam of electrons in order to produce an image on a screen. Cathode ray tubes are also known commonly as CRTs. Cathode ray tubes are widely used in a number of electrical devices, such as computer screens, television sets, radar screens, and oscilloscopes used for scientific and medical purposes. A cathode ray tube consists of five major parts: an envelop…
Club mosses, also called lycophytes, are flowerless and seedless plants in the family Lycopodiaceae, that belong to an ancient group of plants of the division Lycophyta. The lycophytes were one of the dominant plants during the Coal age (360-286 million years ago) and many were shrubs or large trees. By 250 million years ago, most of the woody species had died out. Between 10 and 15 living genera …
Chemical equations reveal the chemical species involved in a particular reaction, the charges and weight relationships among them, and how much heat of reaction results. Equations tell us the beginning compounds, called reactants, and the ending compounds, called products, and which direction the reaction is going. Equations are widely used in chemical engineering, they serve as the basis for chem…
A cation is any atom or group of atoms that has a net positive charge. While matter is electrically neutral overall, ionic compounds are matter that is composed of positively-charged and negatively-charged particles called ions. An ion is any atom or group of atoms with an overall electrical charge. According to the laws of physics, opposite charges attract, so the oppositelycharged ions attract e…
Chemical equilibrium is the final condition of a chemical reaction after the reacting substances have completey reacted. Depending on the reaction, they may reach this condition quickly or slowly, but eventually they will come to a condition in which there are definite, unchanging amounts of all the relevant substances. Chemical equilibrium is one of the most important features of chemical process…
Cats are mammals in the family Felidae of the order Carnivora, which includes all of the carnivores. The highly predatory instincts of species in the cat family are easily seen in domestic cats, for even well-fed individuals will aggressively hunt small mammals and birds. The cat family includes both large species (jaguar, leopard, lion, and tiger) and small ones (bobcat, lynx, ocelot, and serval)…
Cattails or reedmaces are about 10 species of monocotyledonous plants in the genus Typha, comprising the family Typhaceae. Cattails are tall, herbaceous, aquatic plants, growing from stout rhizomes located in shallow sediments of wetlands. The leaves of cattails are long and strap-like, sheathing at the base of the plant, while the spike-like inflorescence is borne by a long cylindrical shoot. The…
The cattle family, Bovidae, is a widespread group of mammals which also includes the goats, sheep, gazelles, antelopes, and goat-antelopes. Of the 107 species currently recognized within this family, just 12 are wild cattle. Even the large muskox (Ovibos moschatus), which looks quite cow-like, is more closely related to the goats than to cattle. Cattle are generally characterized by their large si…
Coal is a naturally occurring combustible material consisting primarily of the element carbon, but with low percentages of solid, liquid, and gaseous hydrocarbons and other materials, such as compounds of nitrogen and sulfur. Coal is usually classified into the sub-groups known as anthracite, bituminous, lignite, and peat. The physical, chemical, and other properties of coal vary considerably from…
Cauterization is the application of heat, mechanically or chemically, to prevent or stop bleeding. It is widely used in surgery to hold bleeding to a minimum and speed the surgical process. Birthmark removal by cauterization with an argon laser. Photograph by Alexander Tsiaras. National Audubon Society Collection/Photo Researchers, Inc. Reproduced by permission. Searing areas of bleeding wi…
Coral reefs are highly diverse ecosystems, supporting greater numbers of fish species and other organisms than any other marine ecosystem. Coral reefs are located in warm, shallow, tropical marine waters with enough light to stimulate the growth of the reef organisms. The primary reef-building organisms are invertebrate animals known as corals; corals secrete the bulk of the calcium carbonate (lim…
Chemical symbols are shorthand abbreviations of the names of the 109 known elements. Each element has its own unique symbol. Since science is an international enterprise, chemical symbols are determined by international agreement. The use of symbols for the chemical elements existed long before a systematic method was developed. The alchemists associated the symbols of the planets not only with th…
A cave is a naturally occurring hollow area inside the earth. Most caves are formed by some type of erosional process. The most notable exception is hollow lava tubes such as those in Hawaii. The formation of caves depends upon geologic, topographic, and hydrologic factors. These factors determine where and how caves develop, as well as their structure and shape. The study of caves is called spele…
Many species of fish have evolved to living under strange conditions, but few are more intriguing than those that have adapted to living in complete darkness. Some of these fish have developed a tendency to live at great depths in the ocean where no light penetrates, while others have found refuge in equally dim locations such as caves, wells, and subterranean streams. This specialization to livin…
The Coriolis effect is a mechanical principle demonstrating that, on a rotating solid body, an inertial force acts on the body at right angles to its direction of motion. The Coriolis effect (also called the Coriolis force) is based on the classic laws of motion introduced to the world by Sir Issac Newton (1642–1727). A rotating body not only moves according to Newtonian motion, but it is a…
The coast and beach, where the continents meet the sea, are dynamic environments where agents of erosion vie with processes of deposition to produce a set of features reflecting their complex interplay and the influences of changes in sea level, climate, sediment supply, etc. "Coast" usually refers to the larger region of a continent or island that is significantly affected by its pr…
Cork is the outer, regenerative bark of the cork oak tree, Quercus suber, family Fagaceae. Unlike other oak species, the cork oak is an evergreen tree and dates from the Oligocene epoch of the Tertiary period. The oldest cork fossil, dating 10 million years old, was found in Portugal and is identical to modern cork. Today cork oak trees grow exclusively around the edge of the Mediterranean, primar…
Coatis are raccoon-like mammals in the family Procyonidae, which have a long ringed tail, typically held perpendicular to the body, and a flexible, upturned, elongated snout. Coatis are also distinctive socially. The females live together in highly organized groups called bands, composed of 5-12 allied individuals, while adult males are solitary. The difference in the social patterning of the sexe…
A corm is a modified, upright, swollen, underground stem base of a herbaceous plant. Corms serve as a perennating organ, storing energy and producing new shoots and flowering stems from one or more buds located in the axils of the scale–like leaves of the previous year. Corms differ from superficially similar bulbs in that their leaves are thin rather than fleshy, and they are entirely comp…
The coca plant, genus Erythroxylum, family Erythroxylaceae, order Linales, is native to the Andean slopes of South America. The genus Erythroxylum comprises approximately 250 species, of which the most cultivated species are Erythroxylum coca (southern Peru and Bolivia) and Erythroxylum novogranatense ( Colombia and northern coastal Peru). The coca plant is a shrub, growing to about 15 ft (5 m). C…
Cormorants or shags are long-necked, generally black or dark grey, aquatic birds in the family Phalacrocoracidae. These birds occur in most temperate and tropical marine coasts, and on many large lakes. There are 29 species of cormorants with fewer species occurring at higher latitudes. The plumage of cormorants is not completely waterproof, since these birds lack an oil gland for preening, so the…
Celestial coordinates locate objects on the sky, which is considered to be an infinitely large (celestial) sphere. The four conventional celestial coordinate systems are defined. These are based on the earth's rotation, which produces an apparent westward rotation of the celestial sphere around the NCP and SCP. An object's arc distance along its hour circle from the celestial equator…
According to Native American legends of the American Southwest, the Indian people have occupied four (some say five) worlds since the creation of man. The present world is the fourth world and each of the three former worlds lies under the one succeeding it. Some legends say that maize, or corn as Europeans came to call it, was already present in the first world, at the time the first humans were …
Coronal mass ejections (CMEs) are explosive and violent eruptions of charged, magnetic field-inducing particles and gas (plasma) from the Sun's outer coronal layer. The ejection from the Sun's corona can be massive (e.g., estimates of CME mass often range in the billions of tons. Ejections propel particles in specific directions, some directly crossing Earth's orbital position…
Chemical synthesis is the preparation of a compound, usually an organic compound, from easily available or inexpensive commercial chemicals. Compounds are prepared or synthesized by performing various chemical reactions using an inexpensive starting material and changing its molecular structure, by reactions with other chemicals. The best chemical syntheses are those that use cheap starting materi…
In geology, the term correlation refers to the methods by which the age relationship between various strata of Earth's crust is established. Such relationships can be established, in general, in one of two ways: by comparing the physical characteristics of strata with each other (physical correlation); and by comparing the type of fossils found in various strata (fossil correlation). Correl…
Cocaine is a colorless or white narcotic crystalline alkaloid derived from the leaves of the South American coca plant—Erythroxylum coca. Aside from its use as a local anesthetic, which has largely been supplanted by safer drugs, its medical applications failed to live up to the hopes of physicians and chemists of the late nineteenth century. They administered cocaine to themselves and othe…
Correlation refers to the degree of correspondence or relationship between two variables. Correlated variables tend to change together. If one variable gets larger, the other one systematically becomes either larger or smaller. For example, we would expect to find such a relationship between scores on an arithmetic test taken three months apart. We could expect high scores on the first test to pre…
Modern celestial mechanics began with Isaac New ton's generalization of Kepler's laws published in his Principia in 1687. Newton used his three laws of motion and his law of universal gravitation to do this. The three generalized Kepler's law are: where G is the Newtonian gravitations factor, and from his second law of motion, Newton derived the following general form of …
Cockatoos are species of birds in the family Cacatuidae, in the order Psittaciformes, which also contains the typical parrots (family Psittacidae). Parrots and cockatoos all have powerful, curved bills, short legs, and strong, dexterous feet with two toes pointing forward and two backward. These birds also have specialized feathers known as powder down, which disintegrates into a powder that is us…
Corrosion is the deterioration of metals and other materials by chemical reaction. Corrosion of metals is the most common type of corrosion and is a process involving an exchange of electrons between two substances, one of them being the metal. In this process, the metal usually loses electrons, becoming oxidized, while the other substance gains electrons, becoming reduced. For this reason, corros…
The celestial sphere is an imaginary projection of the Sun, Moon, planets, stars, and all astronomical bodies upon an imaginary sphere surrounding Earth. The celestial sphere is a useful mapping and tracking remnant of the geocentric theory of the ancient Greek astronomers. Although originally developed as part of the ancient Greek concept of an Earth-centered universe (i.e., a geocentric model of…
Cockroaches are insects in the order Blattaria. They are somewhat flat, oval shaped, leathery in texture, and are usually brown or black in color. Cockroaches range in body size from 0.1 to 2.3 in (2.5 to 60 mm), and are rampant pest insects in human inhabited areas, as well as common outdoor insects in most warm areas of the world. These insects were formerly classified in the order Orthoptera, w…
Codeine is a type of medication belonging to a class of drugs known as opioid analgesics, which are derived from the Papaver somniferum, a type of poppy flower, or are manufactured to chemically resemble the products of that poppy. In Latin, Papaver refers to any flower of the poppy variety, while somniferum translates to mean "maker of sleep." The plant has been used for over 6,000 …
In 1965, Arno Penzias and Robert Wilson announced the discovery of microwave radiation which uniformly filled the sky and had a blackbody temperature of about 3.5K. The pair had been testing a new radio amplifier that was supposed to be exceptionally quiet. What better way to do such a test than to tune the radio so that it should hear nothing at all? After many attempts to account for all extrane…
Codfish (family Gadidae) are a family of bottom-feeding fish that live in cool or cold seas, mostly in the Northern Hemisphere. There are about 21 genera and 55 species of codfishes. The most commonly utilized marine habitats are inshore waters and continental shelves, generally in depths of less than about 300 ft (100 m), but sometimes considerably deeper. Codfishes are voracious predators of sma…
Information for the genetic code is stored in a sequence of three nucleotide bases of DNA called base triplets, which act as a template for which messenger RNA (mRNA) is transcribed. A sequence of three successive nucleotide bases in the transcript mRNA is called a codon. Codons are complimentary to base triplets in the DNA. For example, if the base triplet in the DNA sequence is GCT, the correspo…
The term cosmic ray refers to tiny particles of matter that travel through space. Cosmic rays generally possess an electromagnetic charge and are highly energetic. Physicists divide cosmic rays into two categories: primary and secondary. Primary cosmic rays originate far outside Earth's atmosphere. Secondary cosmic rays are particles produced within Earth's atmosphere as a result of …
A coefficient is a constant multiplier of variables and any part of an algebraic term, Thus, in the expression has 4 as a coefficient of In many formulas, especially in statistics, certain numbers are considered coefficients, such as correlation coefficients in statistics or the coefficient of expansion in physics. …
The coelacanth (Latimeria chalumnae) is the only living representative of an ancient order of fishes, until recently thought to have become extinct 70 million years ago, at about the same time as the dinosaurs. In 1938, however, scientists were astonished when living coelacanths were discovered (this is described later). The coelacanth is a sarcoptergian, or lobe-finned fish, distantly related to …
The coffee tree, genus Coffea, family Rubiaceae (Madder family), is native to Ethiopia. The name coffee also refers to the fruit (beans) of the tree and to the beverage brewed from the beans. Coffee is one of the world's most valuable agricultural crops. There are about 30 species of Coffea, but only two species provide most of the world market for coffee. Coffea arabica is indigenous to Et…
Cosmology is the study of the origin, structure and evolution of the universe. The origins of cosmology predate the human written record. The earliest civilizations constructed elaborate myths and folk tales to explain the wanderings of the Sun, Moon, and stars through the heavens. Ancient Egyptians tied their religious beliefs to celestial objects and Ancient Greek and Roman philosophers debated …
Fraction is the name for part of something as distinct from the whole of it. The word itself means a small amount as, for example, when we ask someone to "move over a fraction." We mean them to move over part of the way, not all the way. Fractional parts such as half, quarter, eighth, and so on form a part of daily language usage. When, for example, we refer to "half an hour,&…
Cotingas are a highly diverse group of birds that make up the family Cotingidae. Species of cotingas occur widely in tropical forests of South and Central America. Cotingas are fly-catching birds, and are similar in many respects to species of tyrant flycatchers (family Tyrannidae), although these families are not closely related. Species of cotingas are extremely variable in size, shape, color, b…
