Star clusters are groups of stars that occur close to each other in space, appear to have roughly similar ages, and therefore, seem to have had a common origin. Star clusters are typically classified into one of two large subgroups, galactic clusters and globular clusters. Galactic clusters are sometimes also known as open clusters. Astronomers have identified thousands of galactic star clusters i…
Star formation is the process by which a cold, dark cloud of gas and dust is transformed into a brilliant star with a surface temperature anywhere from 3,000-50,000K (4,900–90,000°F; 2,700–50,000°C). Many regions of our galaxy are filled with cold clouds of gas that begin to contract, under certain conditions, as a result of their own gravitational attraction. As one of…
Billions of large, essentially independent groups of stars exist in the universe. These are called galaxies. A galaxy is labeled a starburst galaxy if an exceptionally high rate of star formation is found to be taking place within it. This often occurs in galaxies that are in the process of or have recently undergone a merging or collision with another galaxy. Although astronomers do not know exac…
Starfish are marine invertebrates in the phylum Echinodermata, which also includes sea urchins, brittle stars, sea lilies, and sea cucumbers. Starfish belong to the class Asteroidea, which includes 1,500 species inhabiting the shallow margins of all of the world's oceans. Starfish vary widely in appearance. Some species grow up to 3 ft (1 m) in diameter; others are barely 0.5 in (1.3 cm) ac…
Starlings are robust, stocky song birds in the family Sturnidae. They have a stout beak and strong legs, and are included with other perching birds in the order Passeriformes. There are about 110 species of starlings, whose natural range includes Eurasia, Africa, the Pacific islands, and Australia. Starlings are small- to medium-sized birds, ranging in body length from about 4-17 in (10-43 cm), an…
Matter includes all the material that makes up the universe. It has mass and it takes up space. It includes everything around us: the food we eat, the water we drink, the air we breathe, the ores deep within the earth, as well as the atmosphere above it, the substances that make up the moon, and the stars as well as the dust in the tail of a comet. It is fairly easy to observe that matter exists i…
Statistical mechanics is a sub-branch of physics that attempts to explain the behavior of a macroscopic system based on the behavior and properties of that system's microscopic elements. The number of these microscopic elements is usually very large, and it is impossible to accurately predict the behavior of each of these elements as they interact. However, the large number of interactions …
Statistics is that branch of mathematics devoted to the collection, compilation, display, and interpretation of numerical data. In general, the field can be divided into two major subgroups, descriptive statistics and inferential statistics. The former subject deals primarily with the accumulation and presentation of numerical data, while the latter focuses on predictions that can be made based on…
Was there a moment of creation for the universe, or has the universe always existed? The steady-state theory is a cosmological theory for the origin of the universe that suggests the universe has always existed and did not have a moment of creation. This theory was popular during the 1950s and 1960s, but because of observations made during the 1960s, few, if any, astronomers now think that the ste…
A steam engine is a machine that converts the heat energy of steam into mechanical energy by means of a piston moving in a cylinder. As an external combustion engine—since it burns its fuel outside of the engine—a steam engine passes its steam into a cylinder where it then pushes a piston back and forth. It is with this piston movement that the engine can do mechanical work. The stea…
Steam pressure sterilization requires a combination of pressure, high temperatures, and moisture, and serves as one of the most widely used methods for sterilization where these functions will not effect a load. The simplest example of a steam pressure sterilizer is a home pressure cooker, though it is not recommended for accurate sterilization. Its main component is a chamber or vessel in which i…
Stearic acid is a chemical compound consisting of an 18 carbon chain whose terminal carbon is connected to an oxygen atom with a double bond and a hydroxyl group (OH) by a single bond. It belongs to class of materials known as fatty acids, produced primarily from natural fats and oils. Stearic acid is an important component in soap and other cosmetic and industrial preparations. Stearic acid is de…
Steel is the most widely used of all metals, with uses ranging from concrete reinforcement in highways and in high-rise buildings to automobiles, aircraft, and vehicles in space. Steel is iron combined or alloyed with other metals or nonmetals such as carbon. Steel is more ductile (able to deform without breakage) and durable than cast iron and is generally forged, rolled, or drawn into various sh…
The mass of a star determines the ultimate fate of a star. Stars that are more massive burn their fuel quicker and lead shorter lives. Because stars shine, they must change. The energy they lose by emitting light must come from the matter of which the star is made. This will lead to a change in its composition. Stars are formed from the material between stars, shine until they exhaust their fuel, …
Stellar magnetic fields are an array of forces that can be observed surrounding and at the surfaces of stars like the Sun. They are similar in nature to the effect of the well-known dipolar magnets found in science laboratories, classrooms, and toys, but far more powerful and infinitely more complex. They are an important part of the physical makeup of stars because they affect their interiors, at…
Magnitude is the unit used in astronomy to describe a star's brightness in a particular portion of the electromagnetic spectrum. Stars emit different amounts of radiation in different regions of the spectrum, so a star's brightness will differ from one part of the spectrum to the next. An important field of research in modern astronomy is the accurate measurement of stellar brightnes…
Stars fall into distinct groups or populations. The basic stellar populations are Population I stars and Population II stars. The sun and most stars near the sun are Population I stars. They are young second- to third-generation stars with compositions that include 2% of elements heavier than hydrogen and helium. Population II stars, on the other hand, are older stars whose compositions are just h…
It is said that Fred Hoyle once described the evolution of a star as a continual war between nuclear physics and gravity. The structure of a star can be characterized as a polarized battle in that war. The gravity of the stellar material pulls on all the other stellar material striving to bring about a collapse. However, the gravity is opposed by the internal pressure of the stellar gas which norm…
The sun emits a constant stream of particles, mostly protons and electrons, that are known as the solar wind. Many stars also have a similar phenomenon, known as stellar wind. The solar wind is fairly gentle. Stellar winds as gentle as the solar wind are difficult to detect from the earth because other stars are so distant. However, many stars at certain stages in their evolution have very strong …
Stem cells are undifferentiated cells that have the capability of self replication as well as being able to give rise to diverse types of differentiated or specialized cell lines. Stem cells are subclassified as embryonic stem cells, embryonic germ cells, or adult stem cells. Embryonic stem cells are cultured cells that were originally collected from the inner cell mass of an embryo at the blastoc…
Stereochemistry is the study of the three dimensional shape of molecules and the effects of shape upon the properties of molecules. The term stereochemistry is derived from the Greek word stereos, which means solid. …
Sticklebacks are small, bony fish in the family Gasterosteidae that rarely exceed 3 in (8 cm) in body length. Instead of scales, these fish have bony plates covering their body. Sticklebacks are found in North America and northern Eurasia. The name stickleback is derived from the sharp, thick spines arising in the first dorsal fin. The number of these spines forms part of the basis for the identif…
Stilts and avocets are long-legged, long-beaked wading birds of the muddy shores of shallow lakes and lagoons, including both fresh and saline waters. There are fewer than ten species of stilts and avocets all of which are included in the family Recurvirostridae. These birds occur in the temperate and tropical zones of all of the continents except Antarctica. The bill of stilts is rather straight,…
The term stimulus has many meanings; very generally, it is any occurrence (be it an external event, or anything perceived or thought) that causes a detectable response. Stimulus is often used with qualifying terms to further specify its meaning, for example, conditioned stimulus and neutral stimulus. Various fields of study use the term stimulus in different ways. In psychology, it is most often u…
It is possible that ever since people first came to be, stone was used in constructing something: a fence, an oven in a hole or trench, or a shelf in a cave. And it is possible that sometime during this era, someone coined the statement: "Leave no stone unturned." The many cairns and stone hedges erected for religious or astronomical uses were the initial attempts at masonry. However…
Stoneflies or salmonflies are a group of insects with aquatic nymphal stages in the order Plecoptera. Stoneflies have a simple metamorphosis, with three life-history stages: egg, nymph or naiad, and adult. Adult stoneflies have two pairs of membranous wings that are folded back over the abdomen when not in use. Stoneflies are rather weak fliers, and are not usually found very far from the aquatic …
Storks are large wading birds of the tropics and subtropics. They belong to the order Ciconiiformes, which A white stork and its nest in Turkey. JLM Visuals. Reproduced by permission. also includes the ibises and spoonbills. Storks are in the family Ciconiidae. Unlike most tall wading birds, storks will perch in trees. They also nest in high places, and often return to the same nesting sit…
A storm is any disturbance in the atmosphere that has noticeable effects on the earth's surface. The term suggests disagreeable weather conditions that may bring discomfort, inconvenience, economic disaster and loss of human lives. In spite of that fact, storms have a generally positive effect on the environment and on human societies because they are the source of most of the rain and snow…
Storm surge, caused by very low atmospheric pressure, is a volume of oceanic water driven by the wind toward the shore where it "builds up" along the coast producing a localized increase in sea level. Such low atmospheric pressure occurs during cyclonic storms, called typhoons in the Pacific region and hurricanes along the Atlantic seaboard. During these storms, a dome of water forms…
Strata (singular: stratum) are the horizontal layers, or beds, present in most sedimentary rocks. During or immediately after the accumulation of sediments, physical, biological, and chemical processes produce sedimentary structures. Strata are probably the most common sedimentary structures, as almost all sedimentary rocks display some type of bedding. A rock that contains beds is stratified or d…
Stratigraphy is the science of interpreting and describing layers and strata of sediments. Commonly these layers are levels of sedimentary rock, but stratigraphy can also include the study of non-ossified sediments, like those in stream beds and lake bottoms, of inclusions such as volcanic ash and lava, and even the study of different layers of human occupation. Sediment usually forms distinct str…
Stratigraphy is the study of layered materials (strata) that were deposited over time—their lateral and vertical relations, as well as their composition. The basic law of stratigraphy, the law of superposition, states that lower layers are older than upper layers, unless the sequence has been disturbed. Stratified deposits may include soils, sediments, and rocks, as well as man-made structu…
Streams channel water downhill under the influence of gravity. Stream capacity is a measure of the total sediment (material other than water) a stream can carry. Stream competence reflects the ability of a stream to transport a particular size of particle (e.g., boulder, pebble, etc). With regard to calculation of stream capacity and competence, streams broadly include all channelized movement of …
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 …
Also known as twisted-winged parasites, strepsipterans are small insects which are internal parasites of other insects. Measuring between 0.02-0.16 in (0.5 and 4 mm) long, the males and females lead totally different lives. Males are free, winged insects—resembling some forms of beetles—and females are wingless, shapeless insects living as parasites. Strepsipterans live all over the …
Stress is mental or physical tension brought about by internal or external pressures. Researchers have found significant biochemical changes that take place in the body during stress. Exaggerated, prolonged, or genetic tendencies to stress cause destructive changes which lower the body's immune system response and can lead to a variety of diseases and disorders. These include depression, ca…
Environmental stress refers to physical, chemical, and biological constraints on the productivity of species and on the development of ecosystems. When the exposure to environmental stressors increases or decreases in intensity, ecological responses result. Stressors can be natural environmental factors, or they may result from the activities of humans. Some environmental stressors exert a relativ…
String theory (also termed "superstring" theory) is a mathematical attempt to describe all fundamental forces and particles as manifestations of a single, underlying entity, the "string." String theory's predictions are consistent with all known experimental data, and it is felt by some physicists to be a candidate for the long-sought "theory of every thin…
A stroke, also called a cerebral vascular accident or CVA, is a sudden, often crippling disturbance in blood circulation in the brain. Interruption in blood circulation may be the result of a burst artery or of an artery that has become closed off because a blood clot has lodged in it. Blood circulation to the area of the brain served by that artery stops at the point of disturbance, and the brain…
A stromatolite is a preserved structure in sedimentary rock that is a series of thin layers of sediment. These layers formed when a colony of algae trapped loose sediment particles. Stromatolites occur in rocks that range in age from very recent to more than 3.5 billion years old. Ancient stromatolites are the oldest evidence of life that is visible without a microscope. They are also the most com…
Sturgeons are large shark-like fish, with a heterocercal tail like that of a shark and a small ventral mouth behind an extended snout. The mouth has long barbells used for feeding on small animals on the bottom. Sturgeons feed on aquatic insects, snails, crayfish, small clams, and small fish. Sturgeons have a cartilaginous skeleton with bony plates instead of scales in their skin which cover the s…
Subatomic particles are particles that are smaller than an atom. Early in the twentieth century, electrons, protons, and neutrons were thought to be the only subatomic particles; these were also thought to be elementary (i.e., incapable An electronic display of the decay of an upsilon, a particle made of a bottom quark and an antiquark, in the CLEO detector at the CESR collider at Cornell Uni…
The first known treatise on submarines was written in 1578. Published by William Bourne in his Inventions or Devices, the document describes a ship with two hulls, the outer made of wood. While no record exists concerning its manufacture, the ship, according to Bourne, could be submerged or raised by taking in or expelling water from between the double hulls. The first known submarine was built by…
The term subsidence is used in both atmospheric and geological sciences. Atmospheric subsidence refers to the sinking of air that is denser (heavier) than the air below. As it subsides, increasing air pressure compresses the air parcel, causing it to warm. Geologic subsidence is a form of mass wasting that refers to the sinking of geologic materials (rocks or sediments) as underlying materials are…
Making inferences about the nature and structure of buried rock bodies, without access to them, is called subsurface detection. Using geophysical techniques, we obtain data at the surface that characterize the feature buried below. Then we construct models of the feature, trying to invent combinations of reasonable rock bodies which are consistent with all of the observations. Finally, using intui…
Subtraction is the operation that is the inverse of addition. Subtracting a number has the effect of nullifying the addition of that same number. For example, if one adds 11 to 41 then subtracts 11, the result is 41 again. Symbolically, for any numbers a and b, (a + b) - b = a Or one can subtract first, then add: (a - b) + b = a Thus, one can say that subtraction and addition are "inverse o…
Succession is a process of ecological change, involving the progressive replacement of earlier biotic communities with others over time. Succession usually begins with the disturbance of a pre-existing ecosystem, followed by recovery. In the absence of further stand-level disturbance, succession culminates in a stable climax community, the nature of which is determined by climate, soil, and the na…
Suckers are cylindrical fish with a downward-pointing suckering mouth in the family Catostomidae, which is in the large suborder Cyprinoidea, which also includes minnows, carps, and loaches. Most species in the sucker family occur in the Americas, over a range that extends from the boreal forest of North America through much of Central America. A few other species occur in eastern Siberia, and the…
Sudden infant death syndrome (SIDS), also called crib death, is the death without apparent organic cause of an infant under the age of one year. A diagnosis of SIDS can only be made after experts have investigated the death scene, autopsied the dead infant, reviewed the baby's medical history, and ruled out all other possible explanations. About 7,000 babies die of SIDS each year in the Uni…
The possibility of beet sugar was first discovered in 1605 when a French scientist found that the boiled root of garden beet (Beta vulgaris) yielded a syrup similar to that obtained from sugarcane (Saccharum officinarum). It was not until the mid-1700s, however, that the commercial potential of sugar beets was recognized. Once realized, sugar beets quickly became a major crop in Europe and elsewhe…
The sugarcane (Saccharum officinale) is a 12-26 ft tall (4-8 m), perennial, tropical grass (family Poaceae). The tough, semi-woody stems of sugarcane are up to 2 in (5 cm) in diameter, with leafy nodes and a moist internal Harvesting sugarcane. Photo Researchers, Inc. Reproduced by permission. pith containing 15-20% sucrose-sugar. The sugar concentration is highest just before the plant flo…
Sulfur is the non-metallic chemical element of atomic number 16. It has a symbol of S, an atomic weight of 32.07, and a specific gravity of 2.07 (rhombic form) or 1.96 (monoclimic form). Sulfur boils at 832.5°F (444.7°C) and consists of four stable isotopes of mass numbers 32 (95.0%), 33 (0.75%), 34 (4.2%) and 36 (0.015%). Sulfur atoms found in different locations have slightly diffe…
Sulfur is an important nutrient for organisms, being an key constituent of certain amino acids, proteins, and other biochemicals. Plants satisfy their nutritional needs for sulfur by assimilating simple mineral compounds from the environment. This mostly occurs as sulfate dissolved in soil water that is taken up by roots, or as gaseous sulfur dioxide that is absorbed by foliage in environments whe…
One drawback to this approach is that for every ton of sulfur dioxide that reacts, two tons of solid calcium sulfite are produced, and they must be disposed of. Sulfur dioxide is used widely to prevent dried fruits (especially apricots and peaches) from becoming discolored. Sulfur dioxide is a strong reducing agent, and prevents the formation of discolored oxidation products in the fruits. It…
One of the major uses of sulfuric acid is in the production of fertilizers. Phosphate rock is treated with sulfuric acid to produce water soluble phosphates, which are essential for plant growth and survival. It is also the acid used in car batteries. Automobile batteries contain lead, lead oxide, and sulfuric acid. These lead storage batteries are used because they can not only provide the electr…
The Sun is the star at the center of our solar system. It has a diameter of about 420,000 mi (700,000 km) and a surface temperature of 9,981°F (5,527°C). Its visible "surface" is actually a thin gas, as is the rest of its atmosphere and interior. The Sun shines as a result of thermonuclear fusion reactions in its core, and the energy produced by these reactions heats th…
Sunbirds are 105 species of small, lovely birds that make up the family Nectariniidae. Sunbirds occur in Africa, South and Southeast Asia, New Guinea, and Australia. They occupy a wide range of habitats, from forests and savannas to shrubby grasslands, and some agricultural habitats. Sunbirds range in body length from 4-9 in (9-22 cm). The wings are short and rounded, and the tail is quite long in…
Sunspots are relatively dark, temporary spots that appear on the Sun from time to time. The largest of these spots are visible to the naked eye and have been noted by Chinese astronomers since antiquity, but their first mention in Western literature is in The Starry Messenger (1610) by Italian astronomer Galileo Galilei (1564–1642). Sunspot activity—the number of spots on the Sun at …
Superclusters are currently the largest structures known in the universe. Stars and clusters of stars group together into galaxies that can contain anywhere from a few million to a few trillion stars. Galaxies collect into groups known as clusters of galaxies. On a larger scale superclusters are clusters of clusters of galaxies. As clusters of galaxies group into superclusters they leave empty spa…
A superconductor is a material that exhibits zero resistance to the flow of electrical current and becomes diamagnetic (opaque to magnetic fields) when cooled to a sufficiently low temperature. …
A supernova is the massive explosion of a star, and is one of the most violent events in the Universe. There are two types of supernovae. A Type I supernova happens when a dead star called a white dwarf accretes so much matter from a companion star that it becomes unstable and explodes. A Type II supernova occurs when a high-mass star runs out of thermonuclear fuel. In this case, the star's…
Surface tension is the result of the cohesive forces that attract water molecules to one another. This surface force keeps objects which are more dense than water (meaning they should not float) from sinking into it. The surface tension of water makes it puddle on the ground and keeps it in a droplet shape when it falls. If you use a table fork to carefully place a paper clip on the surface of som…
Surgery is the part of medicine which employs operative or manual treatment of disease or injury. Although surgery was practiced in ancient times, modern anesthesia was not developed until the nineteenth century. For centuries, most types of operative surgery involved high risk to patients due to infection. With the development of antiseptic surgical methods in the nineteenth century, the risks li…
Surveying is the apportionment of land by measuring and mapping. It is employed to determine boundaries and property lines, and to plan construction projects. The classic surveyors were the Romans. In order to forge an Empire that stretched from the Scottish border to the Persian Gulf, a large system of roads, bridges, aqueducts, and canals was built, binding the country economically and militaril…
The term "survival of the fittest" was first used by the Victorian naturalist Herbert Spencer as a metaphor to help explain natural selection, the central element of Charles Darwin's revolutionary theory of evolutionary change, first published in 1859 in his famous book, The Origin of Species by Means of Natural Selection. In this extremely influential and important book, Darw…
Sustainable development is the management of renewable resources for the good of the entire human and natural community. Built into this concept is an awareness of the animal and plant life of the surrounding environment, as well as inorganic components such as water and the atmosphere. The goal of sustainable development is to provide resources for the use of present populations without compromis…
Swallows and martins are small fast-flying agile birds in the family Hirundinidae. There are 74 species in this family worldwide, mostly found in open habitats, where they forage aerially for their prey of flying insects. There is no particular biological difference between swallows and martins. Sometimes these names are used interchangeably, as in the case of Riparia riparia, known as the sand ma…
The swamp cypress family is more formally called the Taxodiaceae. This is a family of coniferous trees within the Gymnosperms, that is, plants which produce naked seeds (not in a fruit) borne on scales. These scales are usually arranged to form a cone. Within the Taxodiaceae some species are evergreen, and some deciduous. There are nine genera which contain 16 species. These can be found in temper…
Belonging to the order Synbranchiformes, swamp eels are very slim fish with elongated bodies and reduced fins. Their gill system, which is very small, is linked to other organs to help them breathe air. Swamp eels live in tropical and subtropical habitats. They usually are found in stagnant fresh or brackish water; only one species lives in the sea. These fish are found in Central and South Americ…
Swans are large birds in the waterfowl family, Anatidae, which also includes ducks and geese. There are seven species of swans, occurring on all continents except Antarctica. Three species of swan, the mute swan (Cygnus olor), the tundra swan (C. colombianus), and the trumpeter swan (C. buccinator) breed regularly in North America. Swans have a very long neck, and all North American species have a…
The sweet gale or bayberry family (Myricaceae) is made up of about 50 species of shrubs and trees. Minor economic uses of some species involve the extraction of a fragrant wax from their fruits and cultivation as ornamental shrubs. The foliage of plants in the Myricaceae can be deciduous or evergreen, and the leaves are commonly fragrant when crushed. The flowers are small and occur in catkin-like…
The sweet potato (Ipomoea batatas) is a creeping, vine-like plant that is cultivated in tropical climates for its starchy, nutritious tubers. The sweet potato is in the morning glory family (Convolvulaceae). The sweet potato is sometimes referred to as a yam, but it is quite different from the true yam (Dioscorea batatas), which is another species of tropical root-crop. The sweet potato is a peren…
Swifts are the fastest fliers of all of the small birds, reaching speeds of 172-218 mph (275-349 kph), although 35-80 mph (56-128 kph) is more common. They belong to the family Apodidae, a name meaning "without feet" and a reference to the fact that a swift in flight appears to have no legs or feet. Indeed, the legs of swifts are small and weak so that a swift that lands on the groun…
The swordfish (Xiphias gladius), also known as the broadbill, or the forktail, is the only species in the bony fish family Xiphiidae. The swordfish is highly prized as a food fish, and as a game fish. Its most distinguishing characteristic is the remarkable elongation of the upper jaw, which resembles a long, flattened, serrated sword and can extend up to one-third of the body length. The sword is…
Symbiosis is a word used to refer to intimate relationships among species. Symbioses can involve interactions of individuals of different species, or associations of populations of one or more species. Symbiosis can involve obligate relationships, in which the symbionts cannot live apart in nature, but usually the association is more flexible than this. …
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…
Logic is the study of the rules which underlie plausible reasoning in mathematics, science, law, and other discliplines. Symbolic logic is a system for expressing logical rules in an abstract, easily manipulated form. …
Many real objects and forces at all size scales—subatomic particles, atoms, crystals, organisms, stars, and galaxies—exhibit symmetry, of which there are many kinds. Line or bilateral symmetry, the simplest and most familiar, is the symmetry of by any figure or object that can be divided along a central line and then restored (geometrically) to wholeness by reflecting its remaining h…
Nerve impulses are transmitted through a functional gap or intercellular space between neural cells (neurons) termed the synapse (also termed the synaptic gap). Although nerve impulses are conducted electrically within the neuron, in the synapse they are continued (propogated) via a special group of chemicals termed neurotransmitters. The synapse is more properly described in structural terms as a…
A syndrome is a collection of signs, symptoms, and other indications which, taken together, characterize a particular disease or abnormal medical condition. Medical workers place a heavy reliance on the collection of such indicators in the diagnosis of health problems and disorders. The usual approach is to question patients about the nature of their complaints and then to conduct examinations and…
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…
The virtuoso demands that composers placed on musicians at the end of the 1800s were but a foretaste of things to come in the twentieth century. Members of the orchestra were complaining that the music of contemporary composers was unplayable because of the enormous difficulty of complex orchestral writing styles. With the Paris premiere of Igor Stravinsky's "Le Sacre Du Printemps&#x…
The earliest known talking machine was developed in 1778 by Wolfgang von Kempelen. Eyewitnesses reported that it could speak several words in a timid, childlike voice. While the talking machine's success appears genuine, Baron von Kempelen's accomplishments are not above suspicion. Nine years earlier, he had built a chess-playing machine, which defeated many players, including Napole…
Systems of equations are a group of relationships between various unknown variables which can be expressed in terms of algebraic expressions. The solutions for a simple system of equation can be obtained by graphing, substitution, and elimination addition. These methods became too cumbersome to be used for more complex systems however, and a method involving matrices is used to find solutions. Sys…
When a vertebrate encounters substances that are capable of causing it harm, a protective system known as the "immune system" comes into play. This system is a network of many different organs that work together to recognize foreign substances and destroy them. The immune system can respond to the presence of a disease causing agent (pathogen) in two ways. Immune cells called the B c…
Scarlet tanager (Piranga olivacea). Photograph by Robert J. Huffman. Field Mark Publications. Reproduced by permission. Tanagers are 239 species of extremely colorful, perching birds that make up the family Thraupidae. The evolutionary history and phylogenetic relationships of the tanagers and related birds are not well understood. Recent taxonomic treatments have included the tanagers as a…
Taphonomy is the study of how organisms are preserved in the fossil record (the term is derived from the Greek word taphos, which means grave). Taphonomists seek to understand how an organism died and what happened to its body before and during burial. They also try to determine what factors may have contributed to unequal representation of certain groups in the fossil record due to differences in…
Tapirs, of the family Tapiridae, are large, forest-dwelling mammals with a long flexible snout. They are found in tropical South and Central America, and in southeast Asia. There are four species of tapirs in the single genus, Tapirus. Tapirs are grouped with horses and rhinoceroses in the order Perissodactyla, which are the odd-toed, hoofed mammals. Tapirs have a fourth toe on their front feet. E…
Tarpons are large silvery fish, measuring 4-8 ft (1.3-2.5 m) in length, with large scales, a compressed body, a deeply forked caudal fin, and a long ray extending from the dorsal fin. The mouth is large, and contains rows of sharp, fine teeth, and the lower jaw protrudes outward. Tarpon are among the best known and most impressive of the sportfish. They can live in both freshwater and saltwater. …
Tarsiers are prosimians, or primitive primates, in the family Tarsiidae, found the islands of Southeast Asia. Tarsiers have only 34 teeth, unlike their closest prosimian relatives, the lemurs and lorises, which have 36 teeth. Also, the upper lip of tarsiers is not fastened to the gum underneath, so that the face can be mobile, rather like the more advanced primates, monkeys and apes. Tarsiers are …
Tartaric acid is used making silver mirrors, in the manufacturing of soft drinks, to provide tartness to foods, in tanning leather and in making blueprints. Tartaric acid is used in cream of tartar (for cooking) and as an emetic (a substance used to induce vomiting). It readily dissolves in water and is used in making blueprints. Tartaric acid is a molecule that demonstrates properties of optical …
The Tasmanian devil (Sarcophilus harrisii) is the largest surviving marsupial predator, occurring only on the island of Tasmania in dense thickets and forests. The Tasmanian devil is one of about 45 species of marsupial predators that make up the family Dasyuridae. The Tasmanian devil once occurred widely in Australia and Tasmania. However, the Tasmanian devil became extirpated from Australia foll…
Taste is one of the five senses (the others being smell, touch, vision, and hearing) through which all animals interpret the world around them. Specifically, taste is the sense for determining the flavor of food and other substances. One of the two chemical senses (the other being smell), taste is stimulated through the contact of certain chemicals in substances with clusters of taste bud cells fo…
Taxonomy is the field of biology which deals with the nomenclature, identification, and classification of organisms. There are over one million known species on Earth and probably several million more not yet identified. Taxonomists are responsible for identifying, naming, and classifying all these different species. Systematics is a discipline of biology that explicitly examines the natural varia…
The tea plant Camellia sinensis, which is a member of the plant family Theaceae, is a small evergreen tree that is related to the camellias commonly grown in gardens. Although there are more than 3,000 different types, or grades, of true tea that are produced, nearly all are derived from this single species. Other plants such as peppermint and jasmine, which are also often steeped to yield a hot d…
Tectonics is the study of the deformation of Earth's lithosphere—both the causes of deformation and its effects. Tectonics focuses primarily on mountain-building, but involves other unrelated activities as well. Since the development of the theory of plate tectonics, tectonics has become an especially active area of research in geology. Deformation of rocks, known as tectonism or dia…
A telegraph is any system that transmits encoded information by signal across a distance. Although it is associated with sending messages via an electric current, the word telegraph was coined to describe an optical system of sending coded messages. From its invention until the telephone became a viable system, the telegraph was the standard means of communicating both between and within metropoli…
Telemetry is the science of obtaining quantities or making measurements from a distant location and transmitting them to receiving equipment where they are recorded, monitored, or displayed. A basic telemetry system consists of a measuring instrument or detector, a medium of transmission (sending), a receiver, and an output device that records and displays data. Today, telemetric systems are mainl…
The term telephone (from Greek tele, afar, and phone, sound) in a broad sense means a specific type of Figure 1. Telephone set simplified circuit. Illustration by Hans & Cassidy. Courtesy of Gale Group. telecommunications which permits people to carry direct conversations over almost any distance. The articulate speech is transmitted in a form of either modulated electric current pr…
The telescope is an instrument which collects and analyzes the radiation emitted by distant sources. The most common type is the optical telescope, a collection of lenses and/or mirrors that is used to allow the viewer to see distant objects more clearly by magnifying them or to increase the effective brightness of a faint object. In a broader sense, telescopes can operate at most frequencies of t…
The invention of the cathode ray tube in 1897 by Ferdinand Braun quickly made possible the technology that we call television. Indeed, by 1907, the cathode ray tube was supplying television images. Within 50 years, television had become a dominant form of entertainment and an important way to acquire information. This remains true today, as the average American spends between two and five hours ea…
Temperature is intuitively associated with the sense of hot and cold. Put your finger in a pan of hot water and energy flows as heat from the water to your finger; you say that the water is at a higher temperature than your finger. Now put your finger in a glass of ice water and energy flows as heat in the other direction. The direction of energy flow as heat is the basis of our definition of temp…
An organism maintains homeostasis, a steady internal state, only if its body temperature stays within prescribed limits. Cellular activities require an optimum amount of heat. They depend on enzyme action, and enzymes function within a narrow range of temperature. For this reason, living things can only tolerate a limited rise or drop in temperature from the optimum. Mechanisms exist that regulate…
Tenrecs are four-legged nocturnal mammals belonging to the order Insectivora. Tenrecs have evolved into more distinct forms than any other family of animals within the order. Tenrecs can resemble hedgehogs, moles, shrews, or muskrats, depending on the species. Some species of tenrecs have a long tail and long hind legs, while others have a stumpy tail and short hind legs. A stripped tenrec. P…
A teratogen is an environmental agent that can cause abnormalities in a developing organism resulting in either fetal death or congenital abnormality. The human fetus is separated from the mother by the placental barrier, but the barrier is imperfect and permits a number of chemical and infectious agents to pass to the fetus. Well known teratogens include (but are not limited to) alcohol, excess v…
In general, there are three types of algebraic expressions which can be classified as terms. These include expressions made up of a single variable or constant, ones that are the product or quotient of two or more variables and/or constants, and those that are the product or quotient of other expressions. For example, the number 4 and the variable x are both terms because they consist of a single …
Termites are slender, social insects, ranging in size from 0.007-0.072 in (2-22 mm) long. The reproductive members of the species have wing spans of 0.03-0.3 in (10-90 mm). Inhabiting nests of their own construction, they live in permanent and often highly developed communities. While termites thrive in warm, humid environments, some species have also adapted to open savannas and temperate zones. …
Terns are fast-flying coastal birds in the family Sternidae, which includes some 42 species. Most species of terns are found in the tropics and subtropics, but these birds occur on all continents. They range from the limits Royal terns (Thalasseus maximus) on Estero Island, Florida. Photograph by Robert J. Huffman. Field Mark Publications. Reproduced by permission. of land in the highest A…
The word terrace is applied to geological formations, architecture such as a housing complex built on a slope, or an island between two paved roads. However, Rice terraces in Bali, Indonesia. JLM Visuals. Reproduced by permission. the act of terracing specifies an agricultural method of cultivating on steeply graded land. This form of conservation tillage breaks a hill into a series of ste…
Territoriality is the behavior by which an animal lays claim to and defends an area against others of its species, and occasionally members of other species as well. The territory defended could be hundreds of square miles in size, or only slightly larger than the animal itself. It may be occupied by a single animal, a pair, family, or entire herd or swarm of animals. Some animals hold and defend …
Tetanus, also known as lockjaw, is a disease caused by a type of bacteria that lives in the soil and the intestines of people and animals. When these bacteria get into the body, the poisons they produce affect the nervous system, causing muscle spasms and, in many cases, death. Tetanus is not contagious and can be prevented with a vaccine. Tetanus is caused by the bacteria Clostridium tetani. Teta…
A tetrahedron is a polyhedron with four triangular faces. It is determined by four points (the vertices) that are not all in the same plane. A regular tetrahedron is one where all of the faces are congruent equilateral triangles. A tetrahedron is the same as a pyramid with a triangular base. …
Textiles are generally considered to be woven fabrics. They may be woven from any natural or synthetic fibers, filaments, or yarns that are suitable for being spun and woven into cloth. Spinning is the process of making yarn or thread by the twisting of vegetable fibers, animal hairs, or man-made fibers, i.e., filament-like elements only a few inches in length. In the spinning mill, the raw materi…
Thalidomide is a drug that was marketed in the late 1950s and early 1960s in Great Britain and Europe. It was used both as a sleeping pill and as an antidote to morning sickness in pregnant women. In 1962, a host of usually rare limb abnormalities suddenly became much more common. About 10,000 babies were born displaying, in particular, a shortening of the arms and/or legs called phocomelia. In ph…
A theorem (the term is derived from the Greek theoreo, which means I look at) denotes either a proposition yet to be proven, or a proposition proven correct on the basis of accepted results from some area of mathematics. Since the time of the ancient Greeks, proven theorems have represented the foundation of mathematics. Perhaps the most famous of all theorems is the Pythagorean theorem. Mathemati…
The most easily observed examples of thermal expansion are size changes of materials as they are heated Figure 1. Representation of thermally induced change in a bimetallic strip made of iron and aluminum. The strip bends because the two materials do not expand or contract equally. Illustration by Hans & Cassidy. Courtesy of Gale Group. or cooled. Almost all materials (solids, liqu…
Accurately measuring temperatures over a wide range is a challenge to engineers, physicists, and other scientists. Many techniques have been devised to deal with a wide range of conditions and temperatures. One such technique is a thermocouple. A thermocouple makes use of one aspect of the thermoelectric effect to measure temperatures, the voltage produced between two different wires with junction…
Thermodynamics is the science that deals with work and heat, and the transformation of one into the other. It is a macroscopic theory, dealing with matter in bulk, disregarding the molecular nature of materials. The corresponding microscopic theory, based on the fact that materials are made up of a vast number of molecules, is called statistical mechanics. The conservation of energy is well known …
A thermometer is a device that registers the temperature of a substance relative to some agreed upon standard. Thermometers use changes in the physical or electronic properties of the device to detect temperature variations. For example, the most common thermometer consists of some sort of liquid sealed into a narrow tube, or capillary, with a calibrated scale attached. The liquid, typically mercu…
A thermostat is a device for controlling heating and cooling systems. It consists of a circuit controlled by a temperature sensitive device and connected to the environmental system. The most common thermostat, such as the one seen in homes and offices, is based on a bimetallic strip. As its name suggests, a bimetallic strip consists of thin strips of two different metals bonded together. One meta…
Thistle is the common name given to some plants in several genera of the Cynareae tribe, family Asteraceae. These genera include Cirsium, Carduus, Echinops, Onopordum, Silybum, Centaurea, and Cnicus. The name thistle most often refers to the weedy, prickly plants belonging to the genera Cirsium and Carduus. Thistles are composite flowers, which means their flower is actually a group of small flowe…
Thoracic surgery refers to surgery performed in the thorax or chest. The anatomy and physiology of the thorax require special procedures to be carried out for the surgery to be done. The thorax is the bony cage consisting of the ribs, the spine, and the breastbone or sternum. The floor of the thorax is formed by the diaphragm. Within the thorax lie the two lungs and the heart, the organs whose fun…
Thrips are minute (less than 0.20 in or 5 mm) slender-bodied insects of the order Thysanoptera, characterized by two pairs of veinless, bristle-fringed wings, which are narrow and held over the back when at rest. Although thrips have wings, they do not fly. There are 4,500 species of thrips worldwide. In North America, there are 694 species of thrips in a number of families in two suborders, the T…
Thrombosis is the formation of a blood clot, or thrombus, in a blood vessel. The process is an exaggeration of a normal and useful event by which the body prevents the loss of blood from veins and arteries as a result of an injury. During thrombosis, the blood clotting process goes beyond the construction of a blockage for a damaged blood vessel and actually produces a solid clump (the clot) that …
Thrushes are a diverse group of about 305 species of common, medium-sized, perching, song birds ranging from 4.5-13 in (11-33 cm) in body length in the family Turdidae. Thrushes occur world-wide in a wide range of habitats, but mostly in forests. Some species of thrushes are common in parks and gardens containing shrubs and trees not intensively treated with insecticides. Examples of these familia…
A thunderstorm is a strong disturbance in the atmosphere bringing heavy rain, lightning, and thunder to areas from one to hundreds of kilometers across. Thunderstorms are formed when humid air near the surface begins rising and cooling. The rising air forms clouds. Lightning over Tamworth, New South Wales, Australia. Photograph by Gordon Garrado. Science Photo Library, National Audubon Societ…
Tides are deformations in the shape of a body caused by the gravitational force of one or more other bodies. All bodies in the universe exert tidal forces on each other, although the effects are generally too small to observe. As far Earth is concerned, the most important tidal phenomena are the ocean and ground tides that occur as a result of the Moon's and the Sun's gravity. …
Time is a measurement to determine the duration of an event, or to determine when an event occurred. Time has different incremental scales (year, day, second, etc.), and it has different ways by which it is reported (Greenwich Mean Time, Universal Time, Ephemeris Time, etc.). …
Tinamous are about 45-50 species of ground-dwelling birds that comprise the family Tinamidae, the only member of the order Tinamiformes. Tinamous have a plump, partridge-like body, but they are not related to the "true" partridges, which are species in the pheasant family (Phasianidae). The evolutionary relationships of tinamous are not well understood, but their closest living relat…
A tissue is a collection of similar cells grouped to perform a common function. Different tissues are made of their own specialized cells that are adapted for a given function. All animal cells are basically similar. Each cell has a cell wall or plasma membrane that surrounds the cell and contains various receptors that interact with the outside area. A nucleus, Golgi apparatus, mitochondria, and …
The tit family, Paridae, consists of 46 species of small birds, variously known as tits, titmice, and chickadees. These are all song birds, in the order Passeriformes. All are rather small birds, ranging in body length from about 4–8 in (11–20 cm), and mostly occurring in forests, shrubby woodlands, and in urban and suburban habitats. This family of birds is widespread, and its repre…
Titanium is a transition metal, one of the elements found in Rows 4, 5, and 6 of the periodic table. It has an atomic number of 22, an atomic mass of 47.88, and a chemical symbol of Ti. …
Toadfish are a poorly known group of marine fishes, the vast majority of which live close to the shoreline but remain close to the sea bed. Unlike most fish, these animals are extremely vocal, with some authorities even reporting that their loud calls can be heard out of water. One North American genus, Porichthys, is more commonly known as the singing midshipman. The calls are produced by muscula…
The true toads are amphibians in the order Anura, family Bufonidae. There are 355 species of toads in 25 genera. The largest group is the genus Bufo, which includes 205 species. Toads are characterized by thick, dry, warty skin, with large poison glands on the side of the head and a relatively terrestrial habit as adults. In contrast, adult frogs have a smooth, slimy skin, and a more aquatic habit…
The tomato, or nightshade family (Solanaceae), contains about 85 genera and 2,300 species. Most of the species are tropical or subtropical in distribution, and a Tomatoes in the field. Photograph by Robert J. Huffman. Field Mark Publications. Reproduced by permission. few are of great economic importance. The region of greatest species richness is Central and South America, but representativ…
Tongue worms are bloodsucking endoparasites with a flattened, tongue-like body, and are in the phylum Linguatulida. The final host of these parasites is a predaceous vertebrate, usually a reptile, but sometimes a mammal or a bird. The intermediate host (in which the parasite lives as a larva) can be any of a number of animals, including insects, fish, amphibians, reptiles, and mammals. The 70 spec…
Tonsillitis is an inflammation or infection of the tonsils, caused by either bacteria or viruses. The tonsils usually become swollen and very painful, making swallowing difficult. Sometimes the tonsils have spots of exudates (usually leukocytes) or pus on the surface. The surface of the tonsils is covered by recesses or crypts (cryptae tonsillares) that may branch and extend deep into the tonsil. …
Topology, which is often described as "rubber-sheet geometry," is a branch of geometry that focuses on distortion. Topology describes mathematically the features of a geometric shape that do not change when the shape is twisted, stretched, or squeezed. Tearing, cutting, and combining shapes do not apply to topology. Topology helps to solve problems about determining the number of col…
A tornado is a rapidly spinning column of air formed in severe thunderstorms. The rotating column, or vortex, forms inside the storm cloud then grows downward until it touches the ground. Although a tornado is not as large as its parent thunderstorm, it is capable of extreme damage because it packs very high wind speeds into a compact area. Tornadoes have been known to shatter buildings, drive str…
According to Isaac Newton, an object at rest will remain at rest, and an object will remain in motion unless acted upon by an outside force. A force, therefore, is what causes any object to move. Any force which causes an object to rotate, turn, or twist is called a torque. Torque is equal to the amount of force being exerted on the object times the object's rotation point to the location w…
A torus is a doughnut-shaped, three-dimensional figure formed when a circle is rotated through 360° about a line in its plane, but not passing through the circle itself. Imagine, for example, that the circle lies in space such that its diameter is parallel to a straight line. The figure that is formed is a hollow, circular tube, a torus. A torus is sometimes referred to as an anchor ring. …
Total solar irradiance is defined as the amount of radiant energy emitted by the Sun over all wavelengths that fall each second on 11 sq ft (1 sq m) outside the earth's atmosphere. By way of further definition, irradiance is defined as the amount of electromagnetic energy incident on a surface per unit time per unit area. Solar refers to electromagnetic radiation in the spectral range of ap…
Toucans are 42 species of familiar, brilliantly colored arboreal birds that make up the family Ramphastidae. Toucans are in the order Piciformes, which also includes the woodpeckers. Toucans range from southern Mexico to northern Argentina and Paraguay. Their usual habitat is tropical and subtropical forests and woodlands, and sometimes more open savanna with clumps of trees. Most species occur in…
Touch is one of the five senses (the others being smell, taste, vision, and hearing) through which animals and people interpret the world around them. While the other senses are localized primarily in a single area (such as vision in the eyes or taste in the tongue), the sensation of touch (or contact with the outside world) can be experienced anywhere on the body, from the top of the head to the …
The towers of Hanoi is an ancient mathematical puzzle likely to have originated in India. It consists of three poles, in which one is surrounded by a certain number of discs with a decreasing diameter. The object of the puzzle is to move all of the discs from one pole onto another pole. The movement of any disc is restricted by two rules. First, discs can only be moved one at a time. Second, a lar…
Toxic shock syndrome (TSS) is a serious, life-threatening disease caused by bacteria called Staphylococcus aureus and less typically, Streptococcus pyrogenes. Common causes of skin and mucous membrane infections, some strains of Staph. aureus and Strep. pyrogenes secrete toxins that initiate a cascade of immune reactions. These immune reactions lead to overproduction of immune proteins, and the ab…
Toxicology is the scientific study of poisons (or toxins). Major topics in toxicology include the detection and chemical analysis of poisons, the study of the metabolic effects of these substances on organisms, and the investigation of methods for treatment of poisoning. The Swiss physician and alchemist Philippus Aureolus, also known as Paracelsus (1493-1541) and said to be the father of the mode…
Trace elements are chemicals that are required by organisms in very small quantities for proper physiological and biochemical functioning. Trace elements commonly occur in organisms in concentrations smaller than about 0.001% of the dry weight (less than 10 parts per million, or ppm). Listed in alphabetical order, the most commonly required trace elements for healthy animal or plant nutrition are:…
Tragopans are members of the attractive bird family Phasianidae, which also includes pheasants, peafowl, partridges, guinea fowl, and turkeys. There are various species of tragopans in Afghanistan, eastward as far as Tibet, and in the Himalayas, in the same area as Ithaginus cruentus, a related short-tailed species. Tragopans, however, are more colorful. Tragopans spend much of their time in the c…
Trains were developed during the Industrial Revolution and were arguably that period's most important product. In many ways railroads made the Industrial Revolution possible. Factories could not run without a constant supply of raw materials, or without a method of moving goods to market. More than anything, the progress of the railroads depended on the development of motive power, which wa…
The medical use of drugs to reduce or relieve anxiety has given rise to a group of medications called an tianxiety agents. These agents include anxiolytics, tranquilizers, and sedatives. Tranquilizers were formerly grouped as either "minor" tranquilizers or "major" tranquilizers. The word major stands for "major psychiatric illness," not heavily sedating o…
A transducer is a device which converts one form of energy to another. Typically, one of these forms is electrical while the other is either mechanical, optical, or thermal. Transducers are usually classified as either input or output devices, depending on the direction in which they transfer energy or information. Input transducers convert some property or effect into an electrical signal, while …
A transformer is an electrical device which changes or transforms an alternating current (AC) signal from A high voltage transformer. Photograph by Tardos Camesi. Stock Market. Reproduced by permission. one level to another. The device typically consists of two sets of insulated wire, coiled around a common iron core. Electrical power is applied to one of these coils, called the primary co…
The term transgenics refers to the process of transferring genetic information from one organism to another. By introducing new genetic material into a cell or individual, a transgenic organism is created that has new characteristics it did not have before. The genes transferred from one organism or cell to another are called transgenes. The development of biotechnological techniques has led to th…
A transistor is a small, solid device capable of amplifying and switching electrical signals. A transistor can be manufactured using a wide variety of materials; most transistors utilize the unique semiconducting properties of silicon or germanium that has been selectively contaminated with other elements (e.g., arsenic, phosophorus, boron, gallium). A transistor is controlled by voltages communic…
The concept of transitivity goes back at least 2,300 years. In the Elements, Euclid includes it as one of his "common notions." He says, "Things which are equal to the same thing are also equal to one another." As Euclid puts it, if a = b and c = b, then a = c, which is equivalent to the modern version, which has "b = c" rather than "c = b." …
A translation is one of the three transformations that move a figure in the plane without changing its size or shape. (The other two are rotations and reflections.) In a translation, the figure is moved in a single direction without turning it or flipping it over. A translation can, of course, be combined with the two other rigid motions (as transformations which preserve a figure's size an…
Transpiration refers to the evaporation of water from a biological surface, such as leaves, skin, or lungs. In its most common usage, however, transpiration refers to the loss of water from plant foliage, occurring through microscopic pores known as stomata. Transpiration is a component of a larger process known as evapotranspiration, which is the evaporation of water from a landscape, including b…
A surgical transplant involves the removal of body parts, organs, or tissues from one person and implanting them into the body of another person. Although the idea of transplantation to cure disease dates back several centuries, transplantation has been considered a viable therapy for only a few decades. The relatively recent growth in transplantation stems primarily from expanding knowledge about…
A trapezoid is a four-sided, two-dimensional polygon. With four sides, a trapezoid is a quadrilateral, just as a square or rectangle or parallelogram. Unlike those forms, however, a trapezoid does not necessarily have to have parallel sides. In other words, all rectangles are trapezoids, but not all trapezoids are rectangles. A trapezium is a subset of trapezoids in which at least two sides are pa…
A tree is a woody plant which has three principle characteristics: (a) the potential to grow to 20 ft (6.1 m) or more in height; (b) the formation of one or more trunks arising from the ground; and (c) the ability to stand on its own without support. Trees provide many products which are important to humans, such as timber, fruits, and nuts. They are also the dominant plants in the world's …
The tree shrews (order Scandentia, family Tupaiidae) comprise a small number of species that are only found in South and Southeast Asia. Five genera (19 species) are recognized. All occur in forested areas, ranging from India and Southwest China eastward through Malaysia, Indonesia (west of Wallace's Line), and the Philippines. Three genera and 10 species occur on the island of Borneo alone…
Trichinosis is a disease caused by the roundworm (nematode) called Trichinella spiralis (T. spiralis). It is readily avoided by proper handling and cooking of certain meats, particularly pork products. …
Triggerfishes are members of the family Balistidae of the order Tetradontiformes. They derive their name from a unique feature of their dorsal fin. The triggerfish can lock the large dorsal spine in an upright position by supporting it with its smaller secondary spine. This protects the fish from predation by larger fish because the erect spine makes the fish hard to swallow or extract from small …
Fats exist in foods—and are usually stored in the body—as Triglycerides. Recent research relating levels of triglycerides in the blood stream to heart attacks in human presents a sometime confusing picture but a mounting level evidence suggests that, along with other indicators, triglyceride levels can be used to predict heart attack risk, especially in women and diabetics. Although …
Tritium is an isotope of the chemical element hydrogen. It has not only a single proton but also two neutrons in the nucleus of its atoms. Although technically it is still the element hydrogen, it has its own chemical symbol, T. Chemically, tritium reacts in exactly the same manner as hydrogen, although slightly slower because of its greater atomic weight. A tritium atom has almost three times the…
Trogons are about 35 species of beautiful arboreal birds that constitute the family Trogonidae. Trogons have a number of peculiar features in their morphology, and are not thought to be closely related to any other groups of living birds. This is why their family is the only one in the order Trogoniformes. Species of trogons occur throughout the tropical and subtropical parts of the world, a bioge…
Trophic levels describe the various stages within ecological food chains or webs. Examples of trophic levels, all of which will be described below, are primary producers, primary consumers or herbivores, and secondary and higher-level consumers, or predators. Food webs are based on the productivity of photosynthetic organisms, such as blue-green bacteria, algae, and plants. These are autotrophic o…
Tropic birds are three species of pan-tropical seabirds that make up the family Phaethontidae, in the order Pelecaniformes, which also includes the pelicans, anhingas, cormorants, gannets, and boobies. Tropic birds are medium-sized seabirds, weighing about 0.9 lb (0.4 kg), and having a body length of 16-18.9 in (41-48 cm). This length does not include their greatly elongated tail feathers, which a…
Tropical cyclones are large circulating storm systems consisting of multiple bands of intense showers and thunderstorms and extremely high winds. These storm systems develop over warm ocean waters in the tropical regions that lie within about 25° latitude of the equator. Tropical cyclones may begin as isolated thunderstorms. If conditions are right they grow and intensify to form the storm …
Nowhere is the prevalence of certain illnesses more striking than in areas where tropical diseases flourish. In many parts of Africa, South America, and Asia, diseases exist that are rarely seen in the United States. These include malaria, which infects from 300 to 500 million people annually and kills up to 2.7 million people every year, and leishmaniasis, which affects some 12 million people int…
The trout-perch belongs to the family Percopsidae, which includes only one genus—Percopsis—with only two species. The fish is found only in the fresh waters of North America. One species (Percopsis omiscomaycus) is found mainly on the eastern side; the other species, the sandroller (P. Transmontana), is native to the west in the regions around the Columbia River Basin. Both species a…
The true bugs are a large and diverse group of about 35,000 species of insects in the order Hemiptera. About 44 families of bugs occur in North America. Bugs typically have a flattened body, and their folded wings cross over their thorax and abdomen, giving a distinctive, cross-like pattern. Some species of true bugs are of great economic importance as pests of agricultural plants. A few species o…
The true eels are elongate bony fish with a snakelike slimy body in the order Anguilliformes. There is one family of freshwater eels (the Anguillidae), and 25 families of exclusively marine eels. The freshwater eels must return to the oceans to spawn. The general characteristics of eels include soft-rayed fins and elongate dorsal and anal fins which merge with the caudal fin. Eels lack pelvic fins…
The true flies are a large and diverse group of commonly observed insects in the order Diptera, comprising more than 100,000 species. About 107 families of flies occur in North America. Flies have distinctive, knob-like structures known as halteres on the back of their thorax. Halteres are highly modified from the hind wings of true flies, while the fore wings are membranous and used for flying. T…
Trumpetfish (Aulostomus maculatus) are bony fish in the family Aulostomidae, found from the Caribbean Sea to as far north as Bermuda. They are named for the trumpet-like shape they exhibit when their mouths are open. Trumpetfish measure up to 2 ft (0.6 m) in length, and have dorsal spines which support separate fins or finlets. They are brownish in color with widespread streaks and spots. Trumpetf…
Tsunami, or seismic sea waves, are a series of very long wavelength ocean waves generated by the sudden displacement of large volumes of water. The generation of tsunami waves is similar to the effect of dropping a solid object, such as a stone, into a pool of water. Waves ripple out from where the stone entered, and thus displaced, the water. In a tsunami, the "stone" comes from und…
Tuataras are unusual, lizard-like animals that are the only living representatives of the order Sphenodonta of the vertebrate class Reptilia. The lineage of the sphenodonts is an ancient one, with a fossil record extending back 200 million years, prior even to the evolution of dinosaurs and the lizards. Until the discovery of tuataras in New Zealand, biologists had believed that this reptilian lin…
A tuber is a swollen, underground storage organ that develops on the roots of certain species of plants. Some types of tubers are highly nutritious, mostly because of their energy content in the form of starch. Agricultural species of plants that develop edible tubers include the white potato (Solanum tuberosum), sweet potato (Ipomoea batatas), tapioca or cassava (Manihot esculenta), and yam (Dios…
Tuberculosis is a disease caused by the bacterium Mycobacterium tuberculosis. The organism infects the lungs and causes a debilitating condition that historically was known as consumption. In the 1970s, scientists considered tuberculosis as largely defeated following the widespread use of antibiotics. Today, multi-drug resistant Mycobacterium tuberculosis has developed, and tuberculosis has reemer…
The true tumbleweeds are various species of herbaceous plants in the amaranth family (Amaranthaceae). These are usually annual plants that develop a spherical, bush-shaped biomass. At the end of the growing season when their small seeds are ripe, the tumbleweeds wither and detach from their base and are blown about by winds, scattering their seeds widely over the surface of the ground. Therefore, …
A tumor (also known as a neoplasm) is an abnormal tissue growth. Neoplasm means "new formation." Tumors can be either malignant (cancerous) or nonmalignant (benign) but either type may require therapy to remove it or reduce its size. In either case the tumor's growth is unregulated by normal body control mechanisms. Usually the growth is not beneficial to the organ in which it…
Tuna are large, fast-swimming bony fish (teleosts of the family Scombridae) found in waters of the world's oceans. All species of tuna are economically important, usually supporting a large commercial fishery, and sometimes a local sport fishery. The largest species is the bluefin tuna (Thunnus thynnus), which can achieve a length of 13 ft (4 m) and weigh up to 1,760 lb (800 kg). Population…
Tundra is a generic name for a low-growing ecosystem found in climatically stressed environments with short and cool growing seasons. Latitudinal tundra occurs in the Arctic and to a much lesser extent in the Antarctic, where the environments are characterized by cool, short growing seasons. Altitudinal tundra occurs under a similar climatic regime, but at the tops of mountains. After temperature,…
Tunneling, also known as the tunnel effect, is a quantum mechanical phenomenon by which a tiny particle can penetrate a barrier that it could not, by any classical or obvious means, pass. Though seemingly miraculous, the effect does have some intuitive characteristics. For instance, thin barriers allow more particles to tunnel than do thick ones, and low barriers permit more tunneling than do high…
Turacos, or touracos, are 18 species of sub-Saharan birds that make up the family Musophagidae, in the order Cuculiformes, which also includes the cuckoos, anis, coucals, and roadrunner. The usual habitat of turacos is dense tropical forests or forest edges. Turacos do not migrate, although they may move locally. Turacos are medium- to large-sized birds, with a body length of 1.2-2.5 ft (38-76 cm)…
A turbine is any of various rotary machines that convert the kinetic energy in a stream of fluid (gas or liquid) into mechanical energy by passing the stream through a system of fixed and moving fans or blades. Turbines are simple but powerful machines that embody Newton's third law of motion which states that for every action there is an equal and opposite reaction. They are classified acc…
Turbulence is the formation of eddies in a fluid (liquid or gas). It is produced whenever a fluid (under certain conditions) is in contact with a solid and there is relative motion between them; for example: when wind flows past a building or past a mountain; when the ocean flows past an island; when a baseball flies by; when a jet plane moves in the stratosphere; or when a river flows past a brid…
Turkeys are relatively large, powerful, ground-feeding, North American birds with colorful, featherless heads, classified in the family Phasianidae. The original range of the common turkey (Meleagris gallopavo) was from extreme southern Ontario to Mexico, but it now occupies a much smaller area. The second species in this family is the ocellated turkey (Agriocharis ocellata), which occurs in south…
Turtles are familiar, four-legged reptiles whose body is enclosed within a bony shell. Turtles constitute the reptilian order Testudines. The 257 living species inhabit all continents except Antarctica, plus many islands, and there are marine turtles in all tropical and temperate oceans. The turtles are separated into two major groups (subclasses) that can be readily identified by the way they ret…
Typhoid fever is a severe infection causing a sustained high fever, and caused by the bacteria Salmonella typhi. S. typhi is in the same tribe of bacteria as the type spread by chicken and eggs, commonly known as "Salmonella poisoning," or food poisoning. S. typhi bacteria, however, do not multiply directly in food, as do the Salmonella responsible for food poisoning, nor does it hav…
Typhus is a disease caused by a group of bacteria called Rickettsia. Three forms of typhus are recognized: epidemic typhus, a serious disease that is fatal if not treated promptly; rat-flea or endemic typhus, a milder form of the disease; and scrub typhus, another fatal form. The Rickettsia species of bacteria that cause all three forms of typhus are transmitted by insects. The bacteria that cause…
Tyrannosaurus rex or T. rex, is easily the most famous of the Tryannosaurids (tyrant reptile). Despite its popularity, T. rex appears to have had a limited range in North America and Asia, and existed for a relatively short period of time. T. rex appeared during the late Cretaceous Period, about 85 million to 65 million years ago. This was toward the end of the Mesozoic Era or the Age of Reptiles,…
The tyrant flycatchers are a large family of perching birds, containing 367 species, and making up the family Tyrannidae in the order Passeriformes. Tyrant flycatchers only breed in the Americas, from the northern boreal forest of Canada, through the rest of North America, Central America, and to South America as far south as Patagonia. Rarely, individual tyrant flycatchers may occur in coastal Eu…
An ulcer is a sore that develops in the lining of the stomach or the duodenum, the short section of small intestine that leads away from the stomach, or on the surface of the skin as a result of infection with bacteria. An ulcer in the stomach is called a gastric ulcer; an ulcer in the duodenum is called a duodenal ulcer; and an ulcer on the skin is called a decubitus ulcer. …
An ultracentrifuge is a mechanical device that separates substances of different densities by spinning them very fast. It greatly reduces the time it would take to separate substances that would eventually separate if left alone. The first successful centrifuge was invented in 1883 by Swedish engineer Carl de Laval. It was used to separate cream from milk. Forty years later, another Swede, chemist…
Ultrasonics or ultrasound, derived from the Latin words "ultra," meaning beyond, and "sonic," meaning sound, is a term used to describe sound waves that vibrate more rapidly than the human ear can detect. Sound waves travel as concentric hollow spheres. The surfaces of the spheres are compressed air molecules, and the spaces between the spheres are expansions of the air…
Ultraviolet astronomy is the study of astronomical objects in the ultraviolet portion of the electromagnetic spectrum. Because Earth's atmosphere prevents ultraviolet radiation from reaching its surface, ground-based observatories cannot observe in the ultraviolet. Only with the advent of space-based telescopes has this area of astronomy become available for research. Ultraviolet radiation …
An unconformity is a widespread surface separating rocks above and below, which represents a gap in the rock record. Unconformities occur when either erosion wears away rocks, or rock deposits never form. Therefore, a time gap exists between when the rocks below the unconformity formed and when those above it formed. Unconformities are classified as three types. The most easily recognized are angu…
Underwater exploration is the relatively recent process of investigating the depths of the sea to understand its physical and chemical characteristics and to learn about the life forms that inhabit this realm. Underwater exploration near the surface and near the shore is an ancient form of earning a livelihood and enjoying the pleasures of the water; but deep-sea exploration is a recent phenomenon…
Ungulates are large grazing animals whose toenails have become enlarged into hooves. There are two orders of ungulates: Perissodactyla and Artiodactyla. Animals in the order Artiodactyla have an even number of toes (usually two) that form a cloven hoof. This order is relatively diverse, containing 82 genera and several hundred species. There are nine families in this order, the most familiar of wh…
Uniformitarianism is commonly oversimplified where stated in geological textbooks as "the present is a guide to interpreting the past" (or words to that effect). This explanation, however, is not correct about the true meaning of uniformitarianism. In order to understand uniformitarianism, one must examine its roots in the Enlightenment era (c. 1750–1850) and how the term has …
A unit of measurement is some specific quantity that has been chosen as the standard against which other measurements of the same kind are made. For example, the meter is the unit of measurement for length in the metric system. When an object is said to be 4 m long, that means that the object is four times as long as the unit standard (1 m). The term "standard" refers to the physical…
Uplift is the process by which the earth's surface slowly rises either due to increasing upward force applied from below or decreasing downward force (weight) from above. During uplift, land, as well as the sea floor, rises. The outer shell of the earth, the crust, divides into moving sections called plates. Uplift, forming mountains and plateaus, usually results as these plates crash into …
Upwellings are a flow to the surface of deep, cold, nutrient-rich waters from greater depths in the ocean. The most extensive upwellings are associated with persistent coastal currents that draw surface water away from or along the coast to be replaced by a surface-ward flow of deeper waters. The most famous of these sorts of regional upwellings are found off the west coast of southern South Ameri…
Uranium is the metallic chemical element with an atomic number of 92. Its symbol is U, atomic weight is 238.0, and specific gravity is 18.95. It melts at 2,071.4°F (1,133°C) and boils at 6,904.4°F (3,818°C). Natural uranium consists of three isotopes of mass numbers 234 (0.00054%), 235 (0.711%) and 238 (99.275%). All are radioactive. …
Uranus is the seventh planet from the Sun. It has a large size (its diameter is almost four times that of Earth) and mass, low mean density, fairly rapid rotation, and well-developed ring (11 components) and satellite (15 members) systems. The planet has a strong magnetic field with a large tilt (58.6°) to its rotation axis and offset (0.3 Uranus radius) from its center. Analysis of the obs…
Urea is a white, crystalline solid also known as carbamide. It is highly soluble in water and is the major molecule used by mammals and amphibians as a means of excreting nitrogenous waste (which generally comes from proteins). It is used in making fertilizers (where it serves as source of nitrogen) and in cattle feed, where it also raises the nitrogen levels. Urea is also used in the manufacturin…
Urology is the branch of medicine that deals with the urinary tract in females and with the urogenital tract in males. In both sexes, the urinary tract consists of the kidneys, ureters, bladder, and urethra. In males, additional structures such as the prostate gland are included in the urogenital system. The problems with which a urologist deals tend to fall into three general categories: infectio…
A vaccine is a medical preparation providing immunity from a vaccine specific disease. Vaccines generally consist of a weakened (attenuated) or killed antigens, associated with a particular disease that are capable of stimulating the body to make specific antibodies to that disease. Vaccines use a variety of different substances ranging from dead microorganisms to genetically engineered antigens t…
Vacuum is a term that describes conditions where the pressure is lower than that of the atmosphere. A sealed container is said to be "under vacuum" in this case whereas it is "pressurized" when the pressure is higher than atmosphere. In a vacuum, it becomes necessary to define pressure microscopically. This means that the pressure, or force per unit area, is determined …
A vacuum tube is a hollow glass cylinder containing a positive electrode and a negative electrode between which is conducted in a full or partial vacuum. A grid between these electrodes controls the flow of electricity. The hollow cylinder of a vacuum tube contains a filament, typically tungsten coated with another metal. When the filament is sufficiently heated by an electric current, it emits el…
Valence refers to a number assigned to elements that reflects their ability to react with other elements and the type of reactions the element will undergo. The term valence is derived from the Latin word for strength and can reflect an element's strength or affinity for certain types of reactions. The electrons in an atom are located at different energy levels. The electrons in the highest…
Radiation belts are enormous populations of energetic, electrically charged particles—principally protons and electrons—trapped in the external magnetic field of a planet. Durable radiation belts exist at the planets Earth, Jupiter, Saturn, Uranus, and Neptune but not at Mercury, Venus, or Mars. Nine artificial radiation belts of Earth were produced during the period 1958-62 by the i…
Van der Waals forces are weak attractive forces between electrically neutral atoms or molecules. They are much weaker than the electrostatic forces which bind charged atoms or molecules (ions) of opposite sign or the covalent forces that bond neighboring atoms by sharing electrons. These forces develop because the rapid shifting of electrons within molecules causes some parts of the molecule to be…
Vapor pressure is a force exerted by the gaseous phase of a two phase—gas/liquid or gas/solid system. All liquids and solids have vapor pressure at all temperatures except at absolute zero, -459°F (-273°C). The pressure of the vapor that is formed above its liquid or solid is called the vapor pressure. If a substance is in an enclosed place the two phase system will arrive to …
A variable is a mathematical symbol which is used to represent a member of a given set and is typically denoted by a letter such as x, y, or z. The idea of a variable, invented during the late sixteenth century, is characteristic of modern mathematics and was not widely used in ancient times. Since a variable reflects a quantity which can take on different values, its use has become a critical par…
Most people regard the stars as constant and unchanging. A character in one of Shakespeare's plays refers to a friend "as constant as the Pole Star." While Shakespeare was probably referring to the constant position of the Pole Star, he did not know about the precession of the equinoxes. Or, if he was referring to the constant light of the Pole Star (Polaris), he was in error …
Variance is one of several measures of dispersion which are used to evaluate the spread of a distribution of numbers. Such measures are important because they provide ways of obtaining information about data sets without considering all of the elements of the data individually. To understand variance, one must first understand something about other measures of dispersion. One measure of dispersion…
Varicella zoster virus is a member of the alphaherpesvirus group and is the cause of both chickenpox (also known as varicella) and shingles (herpes zoster). The virus is surrounded by a covering, or envelope, that is made of lipid. As such, the envelope dissolves readil