1 The Greek word "systema" means union, and scientists use the word "system" to describe a collection of several components that are linked to one another by functional relationships. Everything outside the system is known as the surroundings. Most scientific literature is a description of the components of a system, their relationships with one another, and their relationships with other systems. Although each science has its own systems with their own subject matter and networks of relationships, the formal characteristics of systems are similar for all sciences. The scientific discipline called general systems theory formulates principles that are valid for systems in general, no matter the elements involved and the relations or forces among them.
2 Systems can be divided into two types: closed systems and open systems. A closed system receives no supply of energy from outside and transfers no energy outwards. An open system receives energy from its surroundings and transfers it out again.
3 A closed system is isolated fiom its surroundings. The energy supply of a closed system is limited and is progressively used up by the processes operating within the system. The ability of the system to function decreases as the available energy is exhausted. Without any additional energy supplied from the outside, the system’s processes stop altogether and no further change is possible in the system. A mill wheel supplied with water from a non-refillable container is a closed system. Once the container of water is empty, the wheel no longer turns because there is no water to turn it. In a truly closed system, the water would have to be collected below the mill wheel in a second container to ensure that the system did not supply any energy to the outside.
4 Some scientists argue that there are few truly closed systems in nature, and many define closed systems more broadly as those allowing energy but not mass to cross the system boundary. By this definition, the Earth system as a whole is a closed system. The boundary of the Earth system is the outer edge of the atmosphere, and except for the occasional meteorite, virtually no mass is exchanged between the Earth system and the rest of the universe. However, energy in the form of solar radiation passes from the sun, through the atmosphere to the Earth’s surface, which in turn radiates energy back out to space across the system boundary. Hence, energy passes across the Earth’s system boundary, but mass does not, making it a closed system.
5 In an open system, energy and mass can be transferred between the system and its surroundings. Living organisms are open systems. They absorb light energy or chemical energy in the form of organic molecules and release heat and metabolic waste products, such as carbon dioxide, to the surroundings. Generally, relationships exist between the components of a system and its surroundings, that is, other systems. Each open system is part of a larger system that receives and gives off energy. In an open system, the energy is continually resupplied from sources outside the system. In the example of the mill wheel, if the non-refillable water container is replaced by a reservoir fed continuously by a stream, it becomes an open system because the energy supply is renewed from the outside.
6 The natural environment is made up of open systems. These can behave as closed systems temporarily if the energy supply is halted for a period. If, for example, the stream to the reservoir supplying the mill dries up for a long period, the energy consumption of the mill wheel cannot be balanced by new energy supply. The water in the reservoir is used up, and if the dry period is long enough, the mill wheel stops turning. Eventually, the stream may flow again, filling the reservoir and turning the mill wheel again. This occurs because the stream-reservoir-mill system is itself a part of the Earth’s much larger systems of water circulation and water budget, which include condensation, precipitation, run-off, and evaporation. The water systems receive their energy supply from the Earth’s heat budget, which in turn receives its energy supply from the sun’s radiation.

1 Life satisfaction, which can be defined as general happiness or well being, is related to several demographic and personal qualities. The factor of age is important because the elements that make up life satisfaction may differ from one age to the next. Income is more likely to predict life satisfaction among middle aged and older adults than among young adults. Health is a more significant predictor of happiness among older adults than among the young or the middle aged. However, average levels of life satisfaction do not change significantly with age. Generally speaking, older adults are as satisfied with their lives as are younger or middle-aged adults.
2 There is no single element that guarantees high life satisfaction for everyone who possesses it. Happiness seems to consist of many things that each person weighs differently, such as income, education, work, and relationships. However, certain factors are reliable predictors of life satisfaction. One such predictor is health, especially one’s perception of one’s own health rather than a doctor’s objective health assessment. Another predictor of life satisfaction is a feeling of being in charge of one’s own life and a sense of authority over one’s own decisions. Adults who feel that they have some choices and options are generally happier than those who feel that their lives are controlled by others or by fate or chance. For example, older adults who experience financial strain feel less life satisfaction mainly because the problem signals a loss of control over their lives.
3 The largest predictor of life satisfaction appears to be the adequacy of social relationships, especially marriage and family relationships. The perceived quality rather than the quantity of social interactions is most strongly related to happiness. Satisfaction with one’s close personal relationships is more closely linked to overall life satisfaction than either demographic factors or satisfaction with other key aspects of adult life such as occupation. This is true even among highly educated men, who typically have a very high commitment to their work. The quality of social support available in one’s key relationships affects the ability to handle stress and life changes as well as one’s ongoing level of life satisfaction.
4 Studies suggest that family background and early-adulthood resources are predictors of psychological health or success at midlife. People who age well are those who start out well. One study showed that the happiest and most successful middle-aged adults had grown up in warm, supportive, intellectually stimulating families. Well-adjusted or successful middle-aged adults began adulthood with more personal resources, including better psychological and physical health at college age. They also had been practical and well organized in college and had shown greater intellectual competence.
5 However, no measure of early family environment or early-adult competence remained a significant predictor of psychological well being at the end of middle age. One study of men revealed that at the age of 65, there were no childhood or early-adulthood characteristics that distinguished between men who had turned out well and those who had not. However, what did predict success and well being at age 65 was the men’s health and adjustment at midlife. These results suggest that a successful adult life is not something preordained from childhood or early adulthood but rather something created out of the opportunities available over the course of one’s life. Late-life success is related more directly to midlife qualities or experiences. People who start out with certain advantages have a greater chance of experiencing further advantages; however, it is what one does with the experiences-both positive and negative-that determines long-term life satisfaction. The choices that people make in early adulthood help shape who they are at midlife, and those midlife qualities in turn influence who they become later in life.
Glossary:
demographic: relating to demography, the study of human populations

1 Until the nineteenth century, most tall buildings were constructed of load-bearing masonry walls. Masonry walls had to be thick, particularly at the base, to support a building’s great weight. Stoneworkers built these walls by placing stone upon stone or brick upon brick, adding strength and stability by placing layers of mortar or cement between the stones. Floors and roofs had to be supported by wooden beams, but the major vertical force of buildings was supported by thick masonry walls. This imposed serious limitations on the number and size of windows.
2 In the 1850s, an alternative was emerging that would eliminate the need for exterior weight-bearing walls: a three-dimensional grid of metal beams and columns. The introduction of metal construction made it possible to build larger interior spaces with fewer columns than before. The new construction was capable of supporting all the loads to which a building might be subjected, including the vertical forces caused by the weight of the floors and the horizontal forces caused by the wind or earthquakes.
3 The first buildings to depart from the load-bearing wall tradition were iron-framed. Wrought iron, shaped by hammering the heated metal or roiling it under extreme pressure, contains almost no carbon, and when used as floor beams, it can support a great deal of weight. An interior wrought iron skeleton supported all of the hnilding’s weight. Exterior walls of reinforced concrete acted mainly as weatherproofing.As masonry yielded to concrete, walls that once bore weight evolved into thin curtain walls that would allow more windows. These modifications produced sturdier, lighter, and taller buildings that quickly became known as skyscrapers. Skyscrapers satisfied the growing need for office space, warehouses, and department stores. Buildings of eight or more stories quickly transformed the city skyline and dominated the central business districts of American cities such as New York, Chicago, and St. Louis.
4 Skyscrapers differed from previous tall structures with their use of technical innovations such as cast iron and the elevator. The development of cast iron technology, in which molten iron is poured into a mold, made modern plumbing possible. Cast iron pipes, fittings, and valves could deliver pressurized water to the many floors of tall buildings and drain wastewater out. The invention of the mechanical elevator made it possible to construct even taller buildings. Before the elevator, office buildings were rarely more than four or five stories high. In 1857, the first passenger elevator equipped with safety brakes prevented the elevator from falling to the basement when a cable broke. The elevator made the upper floors as rentable as the first floor, liberating architecture from dependence on stairways and human muscle.
5 Not only did these innovations have important uses in the engineering of tall buildings, but they also erased the traditional architectural distinctions separating the bottom, middle, and top of a building. Architects designed towers that reached to the heavens in a continuous vertical grid. Iron construction established the principle of repetitive rhythms as a natural expression of construction, as well as the idea that buildings could be made of new materials on a vast scale.
6 Construction techniques were refined and extended over the next several decades to produce what architectural historians have called "true skyscrapers," buildings over twenty stories high. The invention of steel was particularly significanti as steel T-beams and I-beams replaced iron in these new structures. Steel weighs less than half as much as masonry and exceeds both masonry and iron in tension and compression strength as well as resistance to fatigue. Steel rivets replaced iron bolts and were in turn replaced by electric arc welding in the 1920s. The skyscraper’s steel skeleton could meet all of the structural requirements while occupying very little interior space. Exterior curtain walls could be quite thin, since their only function now was to let in light and keep the weather out.

1 Film is an illusion because the moving pictures seen on the screen are not moving at all. A fihn is actually a series of tiny still pictures, or flames. They appear to be moving because the retina of the human eye retains the impression of an object for a split second after that object has actually disappeared. This principle is known as the persistence of vision. When we look at a single frame of film, the image persists in the brain’s visual center for a fraction of a second. Then, the next frame comes along and the brain has to catch up with the new image. Thus, our eyes and brain trick us into thinking that we see a smoothly moving image rather than a series of still ones.
2 Another illusion of film is known collectively as special effects, the tricks and techniques that filmmakers use when makeup, costume, and stunts are still not enough to make a scene convincing. Special effects artists apply science to filmmaking, showing us things that no plain camera could ever photograph. Even since the introduction of computer graphics in recent decades, the films of today still rely on some special effects that have existed since the early years of cinema.
3 One category of special effects is called optical or visual effects, tricks made with the camera. One of the pioneers of optical effects was the French filmmaker Georges Méliès, who invented a technique called stop-motion photography. With this technique, a scene is filmed, the camera is stopped, the scene is changed in some way, and then the camera rolls again. Stop motion photography can create th.e illusion of an actor disappearing on screen. In one short film, an actor’s clothes keep returning to his body as he tries to get undressed. Méliès also invented a technique known as split screen. By putting a card over the camera lens, he prevented half of the frame of fihn from being exposed. He filmed a scene on the uncovered half of the frame and then backed up the same strip of fihn in his camera. For the second shot, he covered the exposed half and took another series of pictures on the half that had been covered the first time. With the technique of split screen, it is possible to achieve illusions such as having the same actor play twins.
4 Mechanical effects are another category of special effects. Mechanical effects are objects or devices used during the filming to create an illusion, such as feathers or plastic chips to simulate snow, and wires to create the illusion that people are flying. Many sound effects are mechanical effects. Wood blocks create a horse’s hoofbeats, and a vibrating sheet of metal sounds like thunder. During the silent film era, the music machine called the Kinematophone was popular because it could produce the sounds of sirens, sleigh bells, gunfire, baby cries, and kisses-all at the press of a key.
5 Other mechanical effects are puppets, robots of all sizes, and tiny copies of buildings or cities. To reduce the cost of studio sets or location photography, special-effects technicians create painted or projected backgrounds, which replace the set or add to it. For example, in a long shot of a town, the set might be only a few feet high, and the remainder of the town is painted onto a sheet of glass positioned in fiont of the camera during filming. In a 1916 silent film called The Flying Torpedo, mechanical effects created the appearance of an enemy invasion of the California seacoast. Technicians threw small contact-rigged explosives into toy cities, scattering the tiny buildings into the air. An artist painted a row of battleships on a board that was only six feet long. Carpenters drilled small holes in the ships, which were filled with small charges of flash powder to simulate guns. An electrician wired the charges so they could be fired on cue from a small battery. For audiences of the time, the effect was of a real fleet of ships firing on the California coast.
6 Sometimes optical and mechanical effects are used together. For the original 1933 version of King Kong, the filmmakers wanted to show the giant ape climbing the Empire State Building in New York City. To show Kong’s climb, the special-effects technicians built a tiny movable model of the ape and a proportionately small model of the Empire State Building. Then, stop-motion photography was used to create the illusion that Kong was moving up the building.

1 The presence or absence of water has a direct bearing on the possibility of life on other planets. In the nineteenth century, it was commonly accepted that life, perhaps even intelligent life, was widespread in the solar system, and Mars was an obvious target in the search for life. New photographic technology offered a way for astronomers to learn more about the red planet. In 1888, Italian astronomer Giovanni Schiaparelli produced images that showed a network of long, thin, dark lines crossing the surface of Mars. He called these features canali in Italian, which became "canals" or "channels" in English. The strange appearance of the canals suggested to some scientists that they had been formed artificially rather than naturally. The mystery deepened when Schiaparelli observed that many of the canals in the photographs were actually double.
2 Other photographic images of Mars revealed its seasonally changing polar ice caps and features that appeared to be ancient islands located in what was now a dry streambed. When the islands were first discovered, some scientists speculated that a thick water-laden atmosphere capable of generating heavy rains had once existed on Mars. However, others remained unconvinced of the presence of water. Then, in 1963, a team of astronomers obtained a good photographic plate of the near-infrared spectrum of Mars. The photograph showed that, faintly but definitely, water vapor lines could be seen. This photograph established that there really was water on Mars, though the amount was very small. Today, the presence of water vapor in the Martian atmosphere is generally accepted, as is the belief that the atmosphere was once much denser than it is now, with a much greater abundance of water vapor.
3 The surface of Mars is dry today, but it does contain significant amounts of ice and signs that liquid water once flowed over the planet. All of the locations where evidence of water has been found are ancient, probably formed very early in Martian history. Data transmitted from spacecraft on Mars in 2004 have revealed that water was once common across a vast region of the planet, possibly as shallow lakes or seas that dried out and then filled up again. There are signs that the wind blew debris around during dry stages. These seas and lakes extended across hundreds of thousands of square miles, creating habitable conditions during long stretches of time billions of years ago.
4 Evidence of water includes the presence of various minerals known as evaporates, deposits left behind when liquid water turns to vapor. Small areas of mineral deposits have been found in Valles Marineris, a huge hole on Mars that is larger than the Grand Canyon on Earth. The minerals there contain water, so they had to be formed in the presence of water. Geologic research has also turned up clay and gypsum deposits that were formed by water in the soil. Rocks that clearly formed in water extend throughout 300 meters of layered materials in several locations across the Martian plains. The layers were built up over time, which means water was present, at least temporarily, for extended periods on ancient Mars.
5 Besides the ice packs at Mars’s poles, astronomers have discovered a frozen sea near its equator. This frozen sea is the size of the North Sea on Earth and appears similar to the ice packs on Antarctica. Scientists have also detected evidence of lava flows 20 million years ago as well as signs that some volcanoes may still be active. Several recently formed volcanic cones near Mars’s North Pole indicate that the planet’s core may interact with the surface, meaning there was both warmth and moisture in the recent pas-circumstances that might have supported life.
6 Liquid water is the key ingredient for life as we know it. Of all the other planets in the solar system, Mars is most like Earth. The fact that water existed on ancient Mars does not necessarily mean life ever emerged there; however, all of the available evidence does suggest that Mars meets all the requirements that are needed for life to exist.

1 The Greek word "systema" means union, and scientists use the word "system" to describe a collection of several components that are linked to one another by functional relationships. Everything outside the system is known as the surroundings. Most scientific literature is a description of the components of a system, their relationships with one another, and their relationships with other systems. Although each science has its own systems with their own subject matter and networks of relationships, the formal characteristics of systems are similar for all sciences. The scientific discipline called general systems theory formulates principles that are valid for systems in general, no matter the elements involved and the relations or forces among them.
2 Systems can be divided into two types: closed systems and open systems. A closed system receives no supply of energy from outside and transfers no energy outwards. An open system receives energy from its surroundings and transfers it out again.
3 A closed system is isolated fiom its surroundings. The energy supply of a closed system is limited and is progressively used up by the processes operating within the system. The ability of the system to function decreases as the available energy is exhausted. Without any additional energy supplied from the outside, the system’s processes stop altogether and no further change is possible in the system. A mill wheel supplied with water from a non-refillable container is a closed system. Once the container of water is empty, the wheel no longer turns because there is no water to turn it. In a truly closed system, the water would have to be collected below the mill wheel in a second container to ensure that the system did not supply any energy to the outside.
4 Some scientists argue that there are few truly closed systems in nature, and many define closed systems more broadly as those allowing energy but not mass to cross the system boundary. By this definition, the Earth system as a whole is a closed system. The boundary of the Earth system is the outer edge of the atmosphere, and except for the occasional meteorite, virtually no mass is exchanged between the Earth system and the rest of the universe. However, energy in the form of solar radiation passes from the sun, through the atmosphere to the Earth’s surface, which in turn radiates energy back out to space across the system boundary. Hence, energy passes across the Earth’s system boundary, but mass does not, making it a closed system.
5 In an open system, energy and mass can be transferred between the system and its surroundings. Living organisms are open systems. They absorb light energy or chemical energy in the form of organic molecules and release heat and metabolic waste products, such as carbon dioxide, to the surroundings. Generally, relationships exist between the components of a system and its surroundings, that is, other systems. Each open system is part of a larger system that receives and gives off energy. In an open system, the energy is continually resupplied from sources outside the system. In the example of the mill wheel, if the non-refillable water container is replaced by a reservoir fed continuously by a stream, it becomes an open system because the energy supply is renewed from the outside.
6 The natural environment is made up of open systems. These can behave as closed systems temporarily if the energy supply is halted for a period. If, for example, the stream to the reservoir supplying the mill dries up for a long period, the energy consumption of the mill wheel cannot be balanced by new energy supply. The water in the reservoir is used up, and if the dry period is long enough, the mill wheel stops turning. Eventually, the stream may flow again, filling the reservoir and turning the mill wheel again. This occurs because the stream-reservoir-mill system is itself a part of the Earth’s much larger systems of water circulation and water budget, which include condensation, precipitation, run-off, and evaporation. The water systems receive their energy supply from the Earth’s heat budget, which in turn receives its energy supply from the sun’s radiation.