SUBFIELDS OF LINGUISTICS The field of linguistics both borrows from and lends its own theories and methods to other disciplines. The many subfields of linguistics have expanded our understanding of languages. Linguistic theories and methods are also used in other fields of study. These overlapping interests have led to the creation of several cross-disciplinary fields. Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. nsory Memory Sensory memory refers to the initial, momentary recording of information in our sensory systems. When sensations strike our eyes, they linger briefly in the visual system. This kind of sensory memory is called iconic memory and refers to the usually brief visual persistence of information as it is being interpreted by the visual system. Echoic memory is the name applied to the same phenomenon in the auditory domain: the brief mental echo that persists after information has been heard. Similar systems are assumed to exist for other sensory systems (touch, taste, and smell), although researchers have studied these senses less thoroughly. American psychologist George Sperling demonstrated the existence of sensory memory in an experiment in 1960. Sperling asked subjects in the experiment to look at a blank screen. Then he flashed an array of 12 letters on the screen for one-twentieth of a second, arranged in the following pattern: Subjects were then asked to recall as many letters from the image as they could. Most could only recall four or five letters accurately. Subjects knew they had seen more letters, but they were unable to name them. Sterling hypothesized that the entire letter-array image registered briefly in sensory memory, but the image faded too quickly for subjects to “see” all the letters. To test this idea, he conducted another experiment in which he sounded a tone immediately after flashing the image on the screen. A high tone directed subjects to report the letters in the top row, a medium tone cued subjects to report the middle row, and a low tone directed subjects to report letters in the bottom row. Sperling found that subjects could accurately recall the letters in each row most of the time, no matter which row the tone specified. Thus, all of the letters were momentarily available in sensory memory. Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. Unconscious, in psychology, hypothetical region of the mind containing wishes, memories, fears, feelings, and ideas that are prevented from expression in conscious awareness. They manifest themselves, instead, by their influence on conscious processes and, most strikingly, by such anomalous phenomena as dreams and neurotic symptoms (see Psychoanalysis). Not all mental activity of which the subject is unaware belongs to the unconscious; for example, thoughts that may be made conscious by a new focusing of attention are termed foreconscious or preconscious. The concept of the unconscious was first developed in the period from 1895 to 1900 by Sigmund Freud, who theorized that it consists of survivals of feelings experienced during infantile life, including both instinctual drives or libido and their modifications by the development of the superego. According to the Swiss psychoanalyst Carl Jung, the unconscious also consists of a racial unconscious that contains certain inherited, universal, archaic fantasies belonging to what Jung termed the collective unconscious. Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. Carl Gustav Jung, one of the earliest pupils of Freud, eventually created a school that he preferred to call analytical psychology. Like Freud, Jung used the concept of the libido; however, to him it meant not only sexual drives, but a composite of all creative instincts and impulses and the entire motivating force of human conduct. According to his theories, the unconscious is composed of two parts; the personal unconscious, which contains the results of the individual's entire experience, and the collective unconscious, the reservoir of the experience of the human race. In the collective unconscious exist a number of primordial images, or archetypes, common to all individuals of a given country or historical era. Archetypes take the form of bits of intuitive knowledge or apprehension and normally exist only in the collective unconscious of the individual. When the conscious mind contains no images, however, as in sleep, or when the consciousness is caught off guard, the archetypes commence to function. Archetypes are primitive modes of thought and tend to personify natural processes in terms of such mythological concepts as good and evil spirits, fairies, and dragons. The mother and the father also serve as prominent archetypes. Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. Meals: Sites visited: Photo and Video notes: Rorschach Inkblot Test The Rorschach Inkblot Test was developed in 1921 by Swiss psychiatrist Hermann Rorschach. He believed that people reveal their personality traits and unconscious thoughts by how they interpret inkblot designs. Psychologists administer the test by showing subjects a series of ten inkblot cards, asking them to describe what they see, and questioning them about their responses. Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. Phrenological Chart Phrenologists believed it was possible to link psychological traits to specific areas of the brain by measuring the bumps and indentations on a person’s skull. Phrenology enjoyed popularity among the lay public during the late 18th and early 19th centuries, but it was eventually discredited as unscientific. Scientists later proved the more general idea that certain mental activities are linked to specific areas of the brain. Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. Science Source/Photo Researchers, Inc. Electroencephalography An electroencephalogram, or EEG, is a recording of the action potential, or electrical, activity of the cerebral cortex of the brain. An EEG is made by attaching electrodes to the scalp, then collecting, amplifying, and recording the electrical impulses of the brain. Microsoft ® Encarta ® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. Prevalence of Mental Disorders This chart illustrates the percentage of people in the United States who experience a particular mental illness at some point during their lives. The figures are derived from the National Comorbidity Survey, in which researchers interviewed more than 8000 people aged 15 to 54 years. Homeless people and those living in prisons, nursing homes, or other institutions were not included in the survey.Encarta Encyclopedia Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. Computer System A typical computer system consists of a central processing unit (CPU), input devices, storage devices, and output devices. The CPU consists of an arithmetic/logic unit, registers, control section, and internal bus. The arithmetic/logic unit carries out arithmetical and logical operations. The registers store data and keep track of operations. The control unit regulates and controls various operations. The internal bus connects the units of the CPU with each other and with external components of the system. For most computers, the principal input device is a keyboard. Storage devices include external floppy disc drives and internal memory boards. Output devices that display data include monitors and Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. Digital logic is a rational process for making simple “true” or “false” decisions based on the rules of Boolean algebra. “True” can be represented by a 1 and “false” by a 0, and in logic circuits the numerals appear as signals of two different voltages. Logic circuits are used to make specific true-false decisions based on the presence of multiple true-false signals at the inputs. The signals may be generated by mechanical switches or by solid-state transducers. Once the input signal has been accepted and conditioned (to remove unwanted electrical signals, or “noise”), it is processed by the digital logic circuits. The various families of digital logic devices, usually integrated circuits, perform a variety of logic functions through logic gates, including “OR,””AND,” and “NOT,” and combinations of these (such as “NOR,” which includes both OR and NOT). One widely used logic family is the transistor-transistor logic (TTL). Another family is the complementary metal oxide semiconductor logic (CMOS), which performs similar functions at very low power levels but at slightly lower operating speeds. Several other, less popular families of logic circuits exist, including the currently obsolete resistor-transistor logic (RTL) and the emitter coupled logic (ELC), the latter used for very-high-speed systems. Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. Digital Circuits and Boolean Truth Tables Digital circuits operate in the binary number system, which means that all circuit variables must be either 1 or 0. The algebra used to solve problems and process information in digital systems is called Boolean algebra; it deals with logic, rather than calculating actual numeric values. Boolean algebra is based on the idea that logical propositions are either true or false, depending on the type of operation they describe and whether the variables are true or false. “True” corresponds to the digital value of 1, while “false” corresponds to 0. These diagrams show various electronic switches, called gates, each of which performs a specific Boolean operation. There are three basic Boolean operations, which may be used alone or in combination: logical multiplication (AND gate), logical addition (OR gate), and logical inversion (NOT gate). The accompanying tables, called truth tables, map all of the potential input combinations against yielded outputs. Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. Oscillator Circuit This illustration shows a simplified schematic diagram of an oscillator circuit. The tuned circuit contains an inductor coil L1, a smaller inductor coil L2, and a capacitor C. Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. Digital Logic and NOR Gate Circuitry Computers use digital logic to perform operations. Digital logic involves making successive “true” or “false” decisions, which may also be represented by 1 and 0, respectively. Logic circuits, which are at the heart of computer chips, are designed to make a series of these decisions via junctures called gates. Gates are designed and arranged to make different kinds of “decisions” about the input they receive. Individual input and output values are always either true or false and are relayed through the circuit in the form of different voltages. This circuit uses 4 NOR gates, each of which makes the decision “neither A nor B.” The NOR operation yields an output of 0 whenever one or more of the input values is 1. The table shows input values (A, B) and output value (F) for the NOR gate. A circuit map (bottom) shows the layout of a NOR gate and its components, indicating voltage values when the inputs are 0,0 and the output is 1. Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. Vacuum Tube Amplifier A vacuum tube amplifier circuit consists of a triode, load resister, batteries, and variable voltage source. The triode is an evacuated glass tube that consists of a cathode C, anode A, and grid G. Battery A heats the filament in the cathode so that electrons are free to move. Battery B maintains a potential difference between the cathode and anode and supplies the energy that the electrons gain when they flow from the cathode to the anode. This flow can be controlled by applying a negative voltage to the grid with Battery C. The higher the negative voltage on the grid, the fewer electrons flow from the cathode to the anode. Small changes in grid voltage from a radio or audio signal S can produce large variations in current flow from cathode to anode and throughout the rest of the circuit. Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. PROCESSING ARCHITECTURE When a computer carries out an instruction, it proceeds through five steps. First, the control unit retrieves the instruction from memory—for example, an instruction to add two numbers. Second, the control unit decodes the instructions into electronic signals that control the computer. Third, the control unit fetches the data (the two numbers). Fourth, the arithmetic/logic unit performs the specific operation (the addition of the two numbers). Fifth, the control unit saves the result (the sum of the two numbers). Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. Blue Deep Blue, the screen of which is seen here as the computer plays chess against Garry Kasparov in 1997, is an IBM supercomputer that uses scalable massively parallel processing technology to solve complex problems. Deep Blue uses 256 processors working together to calculate between 50 and 100 billion chess moves in under three minutes. Real world applications of computers like Deep Blue include forecasting the weather, drug and genetics research, designing clean-up plans for toxic waste, and powering web servers on the Internet. Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. Nervous System Organization The nervous system is composed of the central nervous system and the peripheral nervous system. The central nervous system, which includes the brain and spinal cord, processes and coordinates all incoming sensory information and outgoing motor commands, and it is also the seat of complex brain functions such as memory, intelligence, learning, and emotion. The peripheral nervous system includes all neural tissue outside of the central nervous system. It is responsible for providing sensory, or afferent, information to the central nervous system and carrying motor, or efferent, commands out to the body’s tissues. Voluntary motor commands, such as moving muscles to walk or talk, are controlled by the somatic nervous system, while involuntary motor commands, such as digestion and heart beat, are controlled by the autonomic nervous system. The autonomic nervous system is further divided into two systems. The sympathetic nervous system, sometimes called the “fight or flight” system, increases alertness, stimulates tissue, and prepares the body for quick responses to unusual situations. In contrast, the parasympathetic nervous system, sometimes called the “rest and repose” system, conserves energy and controls sedentary activities, such as digestion. Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. Weather Map, United States This national weather map shows the conditions expected across the United States on a specific day and time. Forecasters compile weather maps after collecting data from a variety of sources, including radar maps and satellite images. As indicated by the coded information, this map calls for snow across most of the northern continental United States, rain in the upper-middle tier of the country, and progressively warmer temperatures to the south. Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. Prevailing Winds The prevailing winds include the doldrums near the equator, the northeast (or southeast) trade winds somewhat above (or below) the equator, the prevailing westerlies near the middle latitudes, and the polar easterlies near the poles. The winds are named with respect to the direction from which they blow. For example, the northeast trade wind blows in the northern hemisphere from the east toward the west. Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. World Precipitation and Average Rainfall Different regions of the earth receive widely differing amounts of rainfall. A band of high precipitation runs along the equator, while bands of low precipitation occur in each of the polar regions and on each side of the tropics, around 30 degrees latitude.Encarta Encyclopedia Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. Tropical Weather Cell The intertropical convergence zone (ITCZ) is a dynamic weather area located near the equator. Sunlight at the equator warms the air, making it rise and thereby creating low pressure at the equator, along with rain-producing cumulonimbus clouds. The rising air eventually cools and sinks back to the surface at latitudes roughly 30° north and south of the equator. The sinking cool air creates high-pressure systems that keep those latitudes relatively dry. The sinking air is drawn back to the low pressure near the equator, creating a flow of air known as the trade winds. Eventually, the trade winds converge near the equator and create the ITCZ. Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. Divisions of the Atmosphere The atmosphere can be divided into a series of layers, based on the air temperature at different altitudes. In two of the layers, the troposphere and the mesosphere, air gets colder as altitude increases. In the other two layers, the stratosphere and the thermosphere, air gets warmer as altitude increases. This second pattern is called a temperature inversion, and it hinders the mixing of air that accompanies vertical air currents. Consequently, air in the troposphere is well mixed, but air in the stratosphere is not. Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. Rainbow A rainbow forms when raindrops separate white sunlight into a spectrum. As sunlight passes through a drop of water, it is first bent and then reflected from the back surface of the drop toward the viewer’s eye. The amount of bending, known as refraction, differs for light of different colors. Red light bends the least and violet light bends the most. Here, a primary rainbow arcs through the sky after a rainstorm. Primary rainbows have red on the outside arc; the colors of secondary bows are reversed . Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. Antarctic Gyre (Current Wheel) All of the oceans are linked by a clockwise flow around the South Pole. This flow is called the Antarctic gyre, or the current wheel. The clockwise flow around the South Pole results from the way currents of the Atlantic, Pacific, and Indian Oceans circulate counterclockwise. Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. Ocean Currents The major surface currents in the world’s oceans are caused by prevailing winds. The currents may be cold, as in the instance of the West Wind Drift, or warm, as the Gulf Stream. Currents circulate in paths called gyres, moving in a clockwise direction in the northern hemisphere and a counterclockwise direction Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. Lines of Latitude and Longitude Geographic grids are intersecting lines drawn on maps and globes. They are used to help locate and describe specific areas. Two sets of lines encircle the globe: lines of latitude and lines of longitude. The parallel lines of latitude are horizontal, running from east to west. The equator is the imaginary line from which latitude is measured; it is equidistant from the poles, dividing the globe into the northern and southern hemispheres. Unlike lines of latitude, which become progressively shorter as they near the poles, all of the lines of longitude are the same length. Longitudinal lines run from north to south, each individual vertical line intersecting both poles. The prime meridian is an arbitrarily selected line from which all of the others are measured. Any location on the globe can be described in terms its angular distance from the reference points of the equator (0° latitude) and the prime meridian (0° longitude).Encarta Encyclopedia Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. Hours of Daylight by Latitude This table shows the varying length of day with latitude. The day length is calculated as the period between the rising and setting of the sun. It does not include the period of twilight before and after sunrise and sunset. Read the months on the left of the table for the northern hemisphere, and the months on the right of the table for the southern hemisphere. Len gth of Da y at Var iou s Lati tud es (in Ho urs and Min ute s on the 15t h of Eac h Mo Mo Eq 10° 20° 30° 40° 50° 60° 70° 80° Pol Mo Microsoft ® Encarta ® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. Hours of Daylight by Latitude This table shows the varying length of day with latitude. The day length is calculated as the period between the rising and setting of the sun. It does not include the period of twilight before and after Januar y 12 :0 11 :3 11 :0 10 :2 9: 37 8: 30 6: 38 0: 00 0: 00 0: 00 July Februar y 12 :0 11 :4 11 :2 11 :1 10 :4 10 :0 9: 11 7: 20 0: 00 0: 00 August March 12 :0 12 :0 12 :0 11 :5 11 :5 11 :4 11 :4 11 :2 10 :5 0: 00 Septem ber April 12 :0 12 :2 12 :3 12 :5 13 :1 13 :4 14 :3 16 :0 24 :0 24 :0 Octobe r May 12 :0 12 :3 13 :0 14 :2 15 :2 17 :0 22 :1 24 :0 24 :0 24 :0 Novem ber June 12 :0 12 :4 13 :2 14 :0 15 :0 16 :2 18 :4 24 :0 24 :0 24 :0 Decem ber July 12 :0 12 :4 13 :1 13 :5 14 :4 15 :3 17 :3 24 :0 24 :0 24 :0 Januar y August 12 :0 12 :2 12 :5 13 :1 13 :4 14 :3 15 :4 18 :2 24 :0 24 :0 Februar y Septem ber 12 :0 12 :1 12 :1 12 :2 12 :3 12 :4 13 :0 13 :3 15 :1 24 :0 March Octobe r 12 :0 11 :5 11 :4 11 :2 11 :1 10 :4 10 :1 9: 03 5: 10 0: 00 April Novem ber 12 :0 11 :4 11 :1 10 :4 10 :0 9: 06 7: 37 3: 06 0: 00 0: 00 May Decem ber 12 :0 11 :3 10 :5 10 :1 9: 20 8: 05 5: 54 0: 00 0: 00 0: 00 June sunrise and sunset. Read the months on the left of the table for the northern hemisphere, and the months on the right of the table for the southern hemisphere. Len gth of Da y at Var iou s Lati tud es (in Ho urs and Min ute s on the 15t h of Eac h Mo Mo Eq 10° 20° 30° 40° 50° 60° 70° 80° Pol Mo Januar y 12 :0 11 :3 11 :0 10 :2 9: 37 8: 30 6: 38 0: 00 0: 00 0: 00 July Februar y 12 :0 11 :4 11 :2 11 :1 10 :4 10 :0 9: 11 7: 20 0: 00 0: 00 August March 12 :0 12 :0 12 :0 11 :5 11 :5 11 :4 11 :4 11 :2 10 :5 0: 00 Septem ber Microsoft ® Encarta ® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. To begin a geodetic survey, geodesists measure several different points to serve as starting coordinates. For example, a point in a survey of the northeastern United States might be the top of Mount Washington in New Hampshire, the highest point in the area. Geodesists would record the latitude, longitude, and height of the peak. The initial survey would include several such points, called control points. These accurately measured points are marked on the ground. The markers usually consist of brass disks set in concrete or steel rods driven into bedrock. Together, the set of control points creates a control network. Measurements taken between control points are used to compute a datum, a consistent set of latitudes, longitudes, and heights that defines a control network. Once the control network is established, geodesists can measure angles, distances, and height differences and then April 12 :0 12 :2 12 :3 12 :5 13 :1 13 :4 14 :3 16 :0 24 :0 24 :0 Octobe r May 12 :0 12 :3 13 :0 14 :2 15 :2 17 :0 22 :1 24 :0 24 :0 24 :0 Novem ber June 12 :0 12 :4 13 :2 14 :0 15 :0 16 :2 18 :4 24 :0 24 :0 24 :0 Decem ber July 12 :0 12 :4 13 :1 13 :5 14 :4 15 :3 17 :3 24 :0 24 :0 24 :0 Januar y August 12 :0 12 :2 12 :5 13 :1 13 :4 14 :3 15 :4 18 :2 24 :0 24 :0 Februar y Septem ber 12 :0 12 :1 12 :1 12 :2 12 :3 12 :4 13 :0 13 :3 15 :1 24 :0 March Octobe r 12 :0 11 :5 11 :4 11 :2 11 :1 10 :4 10 :1 9: 03 5: 10 0: 00 April Novem ber 12 :0 11 :4 11 :1 10 :4 10 :0 9: 06 7: 37 3: 06 0: 00 0: 00 May Decem ber 12 :0 11 :3 10 :5 10 :1 9: 20 8: 05 5: 54 0: 00 0: 00 0: 00 June compute new coordinates for the additional points relative to the original control points. Both the old coordinates and the new coordinates will be consistent, and they can be used for making maps and for many other purposes. In the past, geodesists developed separate networks for horizontal and vertical points. However, at the start of the 21st century, geodesists were developing a unified system that incorporates all three spatial dimensions (north-south direction, east-west direction, and up). In a specialization known as geometric geodesy, geodesists use a simple model of Earth, in the form of a flattened sphere known as an ellipsoid, to compute latitudes, longitudes, and heights. They also determine angles and distances in relation to the surface of this ellipsoid. Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. GPS System The Navstar Global Positioning System (GPS) is a network of 24 satellites in orbit around the earth that provides users with information about their position and movement. A GPS receiver computes position information by comparing the time it takes for signals from three or four different GPS satellites to reach the receiver. Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. They took angle measurements through telescopes attached to steel circles with calibrations inscribed on them. The lines of measurement formed interlocking networks of triangles, 16 km (10 mi) or more on a side. Often, to get lines of sight above trees and hills, the scientists had to build towers, similar to oil-well derricks. Field parties frequently had to camp in the wilderness. Using these methods, a single observation project took months to complete. To survey just the United States required hundreds of such projects. And the resulting measurements were not very accurate: When comparing points across the United States, geodesists could find errors of over 3 m (10 ft). After satellites were launched in the 1960s, scientists found that they could use measurements of radio or other electromagnetic signals from satellites to create a reference system (a set of starting coordinates) that was consistent on a global scale. American scientists and engineers developed the Global Positioning System (GPS), which uses 24 radio-navigation satellites to provide radio signals that are used worldwide. GPS establishes coordinates accurate to within a few centimeters. Using GPS satellites, transcontinental distances can be measured in just a few hours, within an accuracy of a little more than 1 cm (about 0.5 in). Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. Geodesy encompasses other specialized topics. Some geodesists work to ensure the accuracy of map projections. Others analyze measured data and make mathematical adjustments to account for uncertainties in measurements, fluctuations in instruments, and approximations of mathematical models. Still others prepare standards and guidelines for the observation and processing of surveying data Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. A legend is an explanatory list that defines symbols appearing in a map or chart. Some symbols, such as the mountain range and waterfall symbols shown here, may resemble the features they represent.© Microsoft Corporation. All Rights Reserved. For a map to contain a large amount of easily read information, a system of symbols must be employed. Many commonly used symbols have become Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. Previous Media Next Media Media List Appears In Relief Map Relief maps are three-dimensional models of the terrain in an area; on them, color and scale are used to indicate geographical features rather than simply to delineate political boundaries. Because of this feature, relief maps are extensively used in engineering and the military. This map shows portions of Alaska and northwestern Canada. Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. Topographic Map In addition to showing general locations and political boundaries, topographic maps depict the geology and special features of an area. This type of map offers many advantages. For instance, most backpackers use topographic maps to navigate through wilderness, planning their routes with obstacles and landmarks in mind. If they should get lost, they can find their bearings again by aligning their map and compass to a prominent feature observed nearby. A key on each map indicates the distance scales and special symbols (for features such as railroads, schools, airstrips and water towers) used to create it. Generally, the green on a topographic map indicates forest or vegetation, while the white areas indicate areas that are bare of growth. Series of brown lines indicate mountains and hills, showing elevation and relative steepness. Each line represents a specific unit of elevation; where the lines are very close together, the terrain is quite steep. Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. Coastal piloting means navigating within sight of land. In coastal piloting, navigators determine their position more accurately by taking compass bearings—angular measurements of the line of sight between the craft and nearby landmarks or aids to navigation. To take a compass bearing, the navigator looks across the compass toward a charted landmark and reads the degree mark on the dial. The navigator then plots the compass bearing on the chart, drawing a line along the compass bearing that extends from the charted object toward the vessel’s location. This line is called a line of position. The navigator knows the craft lies somewhere on the line of position because that line on the chart duplicates the line of sight between the navigator and the object. The point where one line of position intersects the dead reckoning track is the estimated position. An estimated position is more reliable than a dead reckoning position. The most reliable position is a fix. To obtain a fix, a navigator takes two or more compass bearings, then plots the resulting lines of position on a chart. The fix lies on the point where two or more lines of position intersect. Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. In inertial navigation, a set of highly sophisticated electronic instruments uses the principles of dead reckoning navigation to track a craft’s changing position and maintain its course. In traditional dead reckoning, human error is unavoidable. Steering errors, currents, gusts of wind, and other external forces can drive a ship or an aircraft off course, unbeknownst to even the most skilled human navigator. An inertial guidance system automatically identifies forces that cause steering errors or speed errors and makes the adjustments necessary to bring the craft back on course. Once the craft leaves the starting point, the inertial navigator automatically measures, calculates, and records the craft’s speed and direction, and the changes to them (called accelerations Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. An inertial navigation system has three components: a gyroscope that responds to forces that might throw the craft off course; an accelerometer that interprets the gyroscope’s responses, and a computer that makes necessary adjustments. A gyroscope may be oriented in any direction. When oriented to true north, it serves as a compass that is completely unaffected by Earth’s magnetic field or by the iron and steel on the craft. A gyroscope consists of a spinning wheel balanced in a set of rings, called gimbals, that prevent it from wobbling. The wheel spins in the same direction at a constant speed until an outside force acts on it. It reacts to that outside force in a predictable way that can be detected and interpreted by the accelerometer. Data collected by the gyroscope and accelerometer are sent to the computer, which calculates the craft's position and makes necessary steering adjustments. Inertial guidance also provides information to the human navigator and acts as an automatic pilot. It is so accurate that it enables a pilot to land an aircraft in poor visibility conditions. The early seafarers who first started plying the water about 3500 bc rarely left sight of land. At night they pulled their reed boats up on beaches or anchored in safe harbors identified by landmarks, such as hills, tall trees, or partially submerged rocks. They gave these landmarks colorful names, many of which persist to this day. For example, a sailor may come across rocks or islands named Lone Rock or Sow and Pigs (a big rock surrounded by many little ones). Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. Azimuthal Projection If you imagine a piece of paper touching an illuminated globe at one point, the projection of the globe onto the paper would resemble an azimuthal projection map. Azimuthal projection maps are useful for viewing the polar regions of the world, because the poles usually appear near the center of the map, with longitudinal lines meeting at the poles and spreading away from each other as they move away from the poles. The polar regions are relatively free of distortion, but the distortion increases as the longitudinal lines move toward equatorial areas. Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. Cylindrical Projection If you imagine a paper cylinder wrapped around an illuminated globe, the projection onto the cylinder would resemble a cylindrical projection map. The shape of the continents near the middle of the cylinder would be relatively free of distortion, but the regions near the poles would be stretched out of proportion as in a cylindrical projection map. Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. e scale of a map defines the relationship between distance on the map and the corresponding distance on the earth. (Left,) The units of measurement shown in the scale represent 1000 mi, top, or 1000 km, bottom, on the earth. (Center,) One unit on the map equals a distance of 10,000,000 units on the earth. (Right,) One unit on the map equals a distance of 1,000,000 units on the earth. Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. Robinson Projection A Robinson projection, also called an orthophanic projection, is one way of transferring information from a round globe to a flat map. This type of projection, elliptical in shape, shows the entire world in a single plane. The poles are depicted as lines instead of points. The Robinson projection was designed in 1963 by Arthur H. Robinson of the University of Wisconsin to minimize distortion, particularly near Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. Conic Projection If you imagine a paper cone placed over an illuminated globe, the projection on the cone would resemble a conic projection map. Such a map is relatively free of distortion in the middle latitude regions, and is useful for viewing countries that fall within those regions, such as some European countries. Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. Topography of Venus This radar map shows the topography of the surface of the planet Venus. Red and yellow indicate high continental elevations while blue represents lower basins. Radar measures the time radio waves take to bounce off the surface of Venus and return. Higher elevations return the signal sooner.Encarta EncyclopediaNASA/Science Source/Photo Researchers, Inc. Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. library science, a method of classifying knowledge for the purpose of cataloging books and other library materials, devised by Melvil Dewey. Under this system all knowledge is divided into ten main classes, each of which is designated by a 100-number span. The first class, 000-099, includes general works, such as encyclopedias, newspapers, and periodicals; 100-199 is used for philosophy and psychology; 200-299, religion; 300-399, social sciences; 400-499, language; 500-599, natural sciences and mathematics; 600-699, technology; 700-799, the arts (including sports and recreations); 800-899, literature and rhetoric; 900-999, geography, history, biography, and travel. Each main class is divided into ten subclasses; for example, in the 800s, 810 is used for American literature, 820 for English literature, 830 for German, etc. Each of these in turn is divided; in the 810s, 811 indicates American poetry and 813 fiction. Even more specific breakdowns, to indicate geographic location, chronological period, or the form of the material, are designated by numbers after a decimal point following the third digit. For example, 813.4 is used for American fiction from 1861 to 1900, and 813.46 indicates a work by or about the novelist Henry James. The classification scheme was originally issued by Dewey in a 42-page booklet printed in 1876; the latest of 19 revisions of his Decimal Classification and Relative Index appeared in three volumes in 1979. Although it is used in libraries throughout the world, another classification system, devised by the Library of Congress, has been adopted by many libraries as more practicable for larger and more specialized collections Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. Library of Congress Classification Library of Congress Classification, in library science, a method of classifying knowledge for the purpose of cataloging books and other library materials, devised by the staff of the Library of Congress in Washington, D.C. In the Library of Congress Classification system (familiarly known as LC), all knowledge is divided into 21 large classes, indicated more or less arbitrarily by capital letters—as follows: Within each of these classes, material is arranged from general considerations to specific treatments and from theory to practical applications; specific topics are indicated by combinations of capital letters, and further subject breakdowns by 3-digit numbers. The classification scheme is continually revised. Unlike the Dewey Decimal Classification system, the LC system makes it possible to indicate specific aspects of a subject without long, cumbersome numerical designations. For example, within the N (Fine Arts) classification, NA indicates architecture, NB sculpture, ND painting, NK decorative arts, and so on. ND 813 would be used for books on Spanish painting, and ND 813 G7 would indicate a book specifically about the Spanish painter Francisco José de Goya y Lucientes. Because of its flexibility LC is particularly suited to the needs of research collections, special libraries, and larger libraries in general. For more information on Library of Congress Classification, see Library: Library of Congress Classification. Microsoft ® Encarta ® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. additional subclasses. These new subclasses are introduced in new editions of the Dewey Decimal system, published every six to ten years. Although the names of the principal classes have changed over time, their content has remained stable. Today, the ten primary classes are as follows: 000-090 Generalities 100-190 Philosophy and psychology 200-290 Religion 300-390 Social sciences 400-490 Language 500-590 Natural sciences and mathematics 600-690 Technology (applied sciences) 700-790 The arts; fine and decorative arts 800-890 Literature and rhetoric 900-990 Geography and history Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. classes has the potential to be broken down into smaller multiples of ten. For example, class 500 (natural sciences and mathematics) has the following subclasses: 500-509 Natural sciences 510-519 Mathematics 520-529 Astronomy and allied sciences 530-539 Physics 540-549 Chemistry and allied sciences 550-559 Earth sciences 560-569 Paleontology; paleozoology 570-579 Life sciences; biology 580-589 Plants 590-599 Animals Each of these classes may then be further divided. For example, the subclasses of 540 are as follows: 540 Chemistry and applied sciences 541 Physical and theoretical chemistry 542 Techniques, equipment, and materials 543 Analytical chemistry 544 Qualitative analysis 545 Quantitative analysis 546 Inorganic chemistry 547 Organic chemistry 548 Crystallography 549 Mineralogy Each of these classes may Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. classes has the potential to be broken down into smaller multiples of ten. For example, class 500 (natural sciences and mathematics) has the following subclasses: 500-509 Natural sciences 510-519 Mathematics 520-529 Astronomy and allied sciences 530-539 Physics 540-549 Chemistry and allied sciences 550-559 Earth sciences 560-569 Paleontology; paleozoology 570-579 Life sciences; biology 580-589 Plants 590-599 Animals Each of these classes may then be further divided. For example, the subclasses of 540 are as follows: 540 Chemistry and applied sciences 541 Physical and theoretical chemistry 542 Techniques, equipment, and materials 543 Analytical chemistry 544 Qualitative analysis 545 Quantitative analysis 546 Inorganic chemistry 547 Organic chemistry 548 Crystallography 549 Mineralogy Each of these classes may Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. The Library of Congress Classification system is divided into 21 major classes, using letters for each. The system does not use the letters I, O, W, X, and Y. The major classes of the Library of Congress Classification system are as follows: A General works B Philosophy; psychology; religion C Auxiliary sciences of history D History: General and Old World E-F History: America G Geography; anthropology; recreation H Social sciences J Political science K Law L Education M Music and books on music N Fine arts P Languages and literature Q Science R Medicine S Agriculture T Technology U Military science V Naval science Z Library science Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved. documents. This is different from the Dewey and Library of Congress schemes, which also aim to locate items on the library’s shelves. If a library is also using the Universal Decimal Classification number for shelf location, the assigned top-level call number generally serves that purpose. Since its inception, the Universal Decimal system has developed increased capacity to express multiple concepts by combining notation. The system’s ability to represent multiple subjects of a document and to express the complex relationships of those subjects has made the Universal Decimal Classification a valuable tool in retrieving information from computerized databases. The Universal Decimal Classification system is issued by the International Federation for Documentation, in The Hague, Netherlands, which is responsible for its ongoing revision. Microsoft® Encarta® Encyclopedia 2002. © 1993-2001 Microsoft Corporation. All rights reserved.