Among the many other uses of calcium sulfate are as a pigment in white paints, as a soil conditioner, in Portland cement, as a sizer, filler, and coating agent in papers, in the manufacture of sulfuric acid and sulfur, in the metallurgy of zinc ores, and as a drying agent in many laboratory and commercial processes. …
Words containing the roots calcul- and comput- have existed since antiquity. The study of concepts used to indicate actions, professions, and (mental and material) artifacts suggests that calculation and computation have not been, as canonically assumed, an exclusive concern of modern times. The mere existence of both word clusters throughout the decades (and centuries) prior to World War II also …
Calculus is the branch of mathematics that deals with rates of change and motion. It grew out of a desire to understand various physical phenomena, such as the orbits of planets, and the effects of gravity. The immediate success of calculus in formulating physical laws and predicting their consequences led to development of a new division in mathematics called analysis, of which calculus remains a…
A calendar is a system of reckoning and ordering time beyond the period of a day in a repetitive, usually annual, cycle. A calendar's primary function is regulating and organizing human activities; the word derives from the Latin calendarium or calendra, "account book," and kalendae or "calends," the new moon and first day of the Roman month, when Romans paid the…
There are three units of time which have a direct basis in astronomy: the day, which is the period of time it takes for the Earth to make one rotation around its axis; the month, which is the period of time it takes for the Moon to revolve around the earth; and the year, which is the period of time it takes for the earth to make one revolution around the Sun. The week has an indirect basis in astr…
Calibration is the process of checking the performance of a measuring instrument or device against some commonly accepted standard. A watch, for example, has to be calibrated so that it keeps correct time, agreeing with the international standard. The dials on a radio must also be calibrated so that the correct frequency or station is actually being received. Calibration provides consistency in a …
A caliper is an instrument used for measuring linear dimensions that are not easily measured by devices such as meter sticks or rulers. Two examples of such measurements include the outer dimensions of a pipe or the internal diameter of a glass tube. Although many kinds of calipers exist, they are all designed on a common principle: two legs are hinged at one end to allow movement of the free ends…
A calorie is the amount of energy required to raise the temperature of 1g of pure water by 34°F (1°C) under standard conditions. These conditions include an atmospheric pressure of one atmosphere, and a temperature change from 60° to 62°F (15.5 to 16.5°C). The calorie is also sometimes designated as a gram-calorie or small calorie (abbreviated: cal), to distingui…
Camels and their relatives, the llamas, are longlegged, hoofed mammals in the family Camelidae in order Artiodactyla, whose members have an even number of toes. All camels have a cleft in their upper lip, and all have the ability to withstand great heat and great cold. Camels evolved in North America and spread into South America, Asia, and Africa. Camels in Asia and Africa today have been domesti…
A canal is a man-made waterway or channel that is built for navigation, irrigation, drainage, or water supply. When the word is used today however, it is usually in the context of transport or navigation by boats. Canal transport should not be confused with navigating on a river, because a canal is entirely artificial (although canals are in many cases connected with a natural body of water). Ther…
Cancel refers to an operation used in term mathematics to remove terms from an expression leaving it in a simpler form. For example, in the fraction 6/8, the factor 2 can be removed from both the numerator and the denominator leaving the irreducible fraction 3/4. In this instance the 2 is said to be canceled out of the expression. Canceling is particularly useful for solving algebraic equations. T…
Cancer is not just one disease, but a large group of almost 100 diseases. Its two main characteristics are uncontrolled growth of the cells in the human body and the ability of these cells to migrate from the original site and spread to distant sites. If the spread is not controlled, cancer can result in death. One out of every four deaths in the United States is from cancer. It is second only to …
Canines are species in the carnivore family, Canidae, including the wolves, coyote, foxes, dingo, jackals, and several species of wild dog. The family also includes the domestic dog, which is believed to have descended from the wolf. The Canidae includes 10-14 genera with 30-35 species, depending on the taxonomic treatment. Canines originated in North America during the Eocene era (38-54 million y…
The possibility of cannibalism has been an object of thought and imagination in virtually every society. The idea of consuming human body substance as food or for symbolic purposes invokes emotionally charged cultural and psychological concerns with boundaries between self and other, persons and nonpersons, the meanings of food and ingestion, and the limits of a moral community. Many societies, bo…
A cantilever, also called a fixed end beam, is a beam supported only at one end. The beam cannot rotate in any direction; thus it creates a solid support. The cantilever is considered the third of the three great structural methods, the other two being post-and-beam construction and arch construction. The cantilever thrusts down which is different from the thrust of an arch which is outward agains…
Capacitance is an electrical effect that opposes change in voltage between conducting surfaces separated by an insulator. Capacitance stores electrical energy when electrons are attracted to nearby but separate surfaces. The voltage across an unchanging capacitance value will stay constant unless the quantity of charge stored is changed. If the voltage across a capacitor is increased until charges…
A capacitor stores electrical energy. It is charged by hooking into an electrical circuit. When the capacitor is fully charged a switch is opened and the electrical energy is stored until it is needed. When the energy is needed, the switch is closed and a burst of electrical energy is released. A capacitor consists of two electrical conductors that are not in contact. The conductors are usually se…
Capillaries are microscopic blood vessels that connect small arteries (arterioles) and small veins (venules). Within the tissues, arterioles terminate into a network of microscopic capillaries. Substances move in and out of the capillary walls as the blood exchanges materials with the cells. Before leaving the tissues, capillaries unite into venules, which merge to form larger and larger veins tha…
Capillary action is the tendency of a liquid to rise in narrow tubes or to be drawn into small openings such as those between grains of a rock. Capillary action, also known as capillarity, is a result of the intermolecular attraction within the liquid and solid materials. A familiar example of capillary action is the tendency of a dry paper towel to absorb a liquid by drawing it into the narrow op…
Debates over capitalism in Africa revolve around the best means to rescue the continent from a prolonged period of stagnation and decline. Observers agree that the program, in the absence of a socialist alternative, must focus on capitalist development. There is disagreement, however, over the role of the African state in this process, as well as over whether to make raw materials exports or indus…
The frogmouths, oilbird, potoos, owlet frogmouths, and nightjars are five unusual families of birds that make up the order Caprimulgiformes, and are collectively referred to as caprimulgids. Caprimulgids have a large head, with a short but wide beak that can open with an enormous gape, fringed by long, stiff bristles. This apparatus is used by caprimulgids to catch their food of insects in flight.…
Capybaras, also known as carpinchos or water hogs, are large South American rodents in the family Hydrochaeridae. Hydrochaeris hydrochaeris is the larger of the two species of capybaras, and is the world's largest rodent. It can reach a body weight of 110 lb (50 kg), a body length of 4.5 ft (1.3 m), and a height of 1.5 ft (50 cm). Hydrochaeris isthmius is about half this size. H. hydrochaer…
Carbohydrates are naturally occurring compounds composed of carbon, hydrogen, and oxygen. The carbohydrate group includes sugars, starches, cellulose, and a number of other chemically related substances. For the most part, these carbohydrates are produced by green plants through the process known as photosynthesis. Countless varieties of plants use this process to synthesize a simple sugar (glucos…
Carbon has been known since prehistoric times. It gets its name from carbo, the Latin word for charcoal, which is almost pure carbon. In various forms, carbon is found not only on Earth, but in the atmospheres of other planets, in the Sun and stars, in comets, and in some meteorites. On Earth, carbon can be considered to be the most important of all the chemical elements, because it is the essenti…
The carbon cycle describes the movement of carbon in the atmosphere, where it is in the gaseous form carbon dioxide, through organisms, and then back into the atmosphere and the oceans. Carbon is a central element of the huge diversity of organic chemicals found in living things, such as the many kinds of carbohydrates, proteins, and fats. Energy is contained in the chemical bonds that hold the at…
Carbon dioxide was the first gas to be distinguished from ordinary air, perhaps because it is so intimately connected with the cycles of plant and animal life. When we breathe air or when we burn wood and other fuels, carbon dioxide is released; when plants store energy in the form of food, they use up carbon dioxide. Early scientists were able to observe the effects of carbon dioxide long before …
Carbon tetrachloride is an organic chemical that is commonly used as a solvent. It is also called tetra chloromethane and is composed of molecules that have one carbon atom and four chlorine atoms bonded together in the shape of a tetrahedron. It is made by combining elemental chlorine with simple carbon compounds like methane or carbon disulfide. It is a liquid at room temperature, with a freezin…
A carbonyl group is a group of atoms that consists of a carbon atom covalently attached to an oxygen atom by a double bond: C = O. The carbon atom, to satisfy its valence of 4, must also be attached by covalent bonds to two other atoms. The simplest type of molecule that contains a carbonyl group is a ketone. Other types of molecules that contain carbonyl groups are aldehydes, acids, esters, and a…
A carcinogen is a substance that causes a normal cell to change into a cancerous cell. The word "car cinogen" is derived from Greek and means in English, cancer-causing. Carcinogens fall into two broad categories, naturally occurring substances that are found in food or soil, or artificial substances created by chemists for various industrial purposes. Although the way carcinogens ca…
The coordinated and rhythmic series of muscular contractions associated with the heart comprise the cardiac cycle. In humans, the cardiac cycle can be subdivided into two major phases, the systolic phase and the diastolic phase. Systole occurs when the ventricles of the heart contract. Accordingly, systole results in the highest pressures within the systemic and pulmonary circulatory systems. Dias…
A measure of the number of elements in a group or a set. For example, the number of books on a shelf can be described by a single cardinal number. Similarly, the set can be assigned the cardinal number 3 because it has only three elements. Since cardinal numbers count the number of elements in a set, they are always positive whole integers. If the elements from two sets have a one-to-one relations…
The cardinals and grosbeaks belong to the subfamilies Cardinalinae, of the finch family (Fringillidae), which is the largest of all North American bird families. (Some researchers include the cardinals and grosbeaks with the Emberizidae, the buntings and tanagers). Cardinals and grosbeaks are New World birds, ranging from central Argentina as far north as central Canada. They live primarily in tem…
The caribou or reindeer (Rangifer tarandus) is a northern species of deer occurring in the boreal and arctic regions of North America and Eurasia. At one time, caribou and reindeer were considered to be separate species, but these animals are fully interfertile and are now considered to be the same species. In North America they are called caribou, whereas in Eurasia they are known as reindeer. Ho…
In the literal sense, a carnivore is any flesh-eating organism. However, in the ecological usage of the word, carnivores kill animals before eating them (that is, they are predators), as opposed to feeding on animals that are already dead (the latter are called scavengers or detritivores). Trophic ecology deals with the feeding and nutritional relationships within ecosystems, and this field has de…
Carnivorous plants are botanical oddities that supplement their requirement for nutrients by trapping, killing, and digesting small animals, mostly insects. Carnivorous plants are photosynthetic, and are therefore fundamentally autotrophic. Still, their feeding relationship with animals represents a reversal of the normal trophic connections between autotrophs and consumers. Carnivorous plants hav…
Carp are fish species in the minnow family (Cyprinidae), one of the major groups of freshwater fish. The most familiar species are the common carp (Cyprinus carpio) and the closely related goldfish (Carassius aureus). The minnow family is characterized by having no teeth in the jaws, although well-developed teeth occur on the pharyngeal bones (located behind the gill chamber) and are used to grind…
Carpal tunnel syndrome results from compression and irritation of the median nerve where it passes through the wrist. In the end, the median nerve is responsible for both sensation and movement. When the median nerve is compressed, an individual's hand will feel as if it has "gone to sleep." The individual will experience numbness, tingling, and a prickly pin like sensation ov…
In genetics, the term carrier describes an organism that carries two different forms (alleles) of a recessive gene (alleles of a gene linked to a recessive trait) and is thus heterozygous for that the recessive gene. Although carriers may act to convey and maintain recessive genes within a population by passing them on to offspring, the carriers themselves are not affected by the recessive trait a…
The carrot family (Apiaceae, or Umbelliferae) is a diverse group of about 3,000 species of plants, occurring in all parts of the world. Most Umbellifers are herbaceous, perennial plants, often with aromatic foliage. Some species have poisonous foliage or roots. The leaves are typically alternately arranged on the stem, and in many species they are compound and divided into lobes. The flowers are s…
Carrying capacity refers to the maximum abundance of a species that can be sustained within a given area of habitat. When an ideal population is at equilibrium with the carrying capacity of its environment, the birth and death rates are equal, and size of the population does not change. Populations larger than the carrying capacity are not sustainable, and will degrade their habitat. In nature, ho…
The Cartesian coordinate system is named after René Descartes (1596–1650), the noted French mathematician and philosopher, who was among the first to describe its properties. However, historical evidence shows that Pierre de Fermat (1601-1665), also a French mathematician and scholar, did more to develop the Cartesian system than did Descartes. To best understand the nature of the Ca…
When René Descartes died in 1650, his work had already attracted both critics and followers. In 1632 Cartesian philosophy was being taught in the Netherlands by his disciple Henri Reneri (1593–1639), and by the mid-1630s the far more independently minded Henri Regius (1598–1679) was setting out his own version of Cartesianism in a less guarded and more polemical way than had Des…
Cartilaginous fish such as sharks, skates, and rays are vertebrates whose internal skeleton is made entirely of cartilage and contains no ossified bone. Cartilaginous fish are also known as Chondrichthyes and have one or two dorsal fins, a caudal fin, an anal fin, and ventral fins which are supported by girdles of the internal skeleton. Placoid scales, or dermal teeth, are characteristic of the sk…
Cartography is the creation, production, and study of maps. Cartographers are often geographers who specialize in the combination of art, science, and technology to make and study maps. Some cartographers teach mapmaking skills and techniques, some design and produce maps, and some are curators of map libraries. All cartographers, however, focus on maps as the object of their study or livelihood. …
The cashew family (Anacardiaceae) is a group of about 600 species of plants, most of which are tropical in distribution, although some occur in the temperate zone. Maturing pistachio (Pistacia vera) nuts on a tree in California. © Holt Studios International, National Audubon Society Collection/Photo Researchers, Inc. Reproduced with permission. Almost all members of the cashew famil…
In the fall of 1997, the Cassini spacecraft began a seven-year, 2.175 billion mi (3.5 billion km) journey to Saturn. The 22.3 ft (6.8 m) robotic spacecraft is still functioning perfectly. When it arrives on July 1, 2004, it will spend four years probing the Saturnian system. Cassini, the first spacecraft to visit Saturn since Voyager 2 swung past it in 1980 and the first spacecraft ever to take up…
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…
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…
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…
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…