The history of technology is the study of the changes through which economic, cultural, and military techniques have evolved and of the social, economic, and political consequences those changes have produced. To reach a full understanding of the history of technology, historians cannot confine their attention to instruments and techniques alone but must consider as well a large domain of events, some of them seemingly remote, that have had a bearing on the evolution of technology: the role of the technologist and engineer and their status and training; geography and climate; division of labor; the processes of invention and innovation; the diffusion of knowledge; the technical consequences of research; the relationship between technology and science; traditions of art; and the development of crafts. The history of technology begins with the use of stone tools by the earliest humans--and perhaps even by their prehuman ancestors. The field of study may be divided into four major periods: the Paleolithic (Old Stone Age), beginning about 2.5 million years ago; the Neolithic (New Stone Age) transition, dating from about 9000 BC; agricultural civilization, which originated with the invention of the plow in the 4th millennium BC; and industrial civilization, which covers the past 250 years. These divisions are approximate, schematic, and sometimes extensively overlapping; even today, with agricultural and industrial civilizations existing side by side and each incorporating technology that is characteristic of the other, there also exist isolated groups of people who still employ Stone Age technology. Similarly, rudimentary forms of agriculture (or at least horticulture) may have been practiced occasionally during the Paleolithic, which was characterized by hunting and gathering. The Paleolithic era and the Neolithic transition, which jointly constitute more than 99% of the time span of technological history, lie properly in the domain of the prehistorian--mainly the archaeologist, anthropologist, and paleontologist. Although this article is concerned primarily with the historical era (agricultural and industrial civilizations), a summary of Paleolithic and Neolithic technology will serve to highlight the origins of agriculture. PALEOLITHIC AND NEOLITHIC PRELUDE Paleolithic technology (see \TPaleolithic Period\t) was the creation of both modern humans (Homo sapiens) and at least one extinct species, Homo erectus. Hunting of animals and gathering of eggs, insects, and edible plants were the dominant economic activities. On the evidence of surviving hunting-gathering societies, it may be supposed that a dual economy existed in which men hunted and women gathered. By the end of the Paleolithic, humanity's technological repertoire included stone tools, the use of fire, spears and spear throwers, the bow and arrow, simple oil lamps, pigments, mortars and pestles, and bone sewing needles. The Neolithic transition (see \TNeolithic Period\t) is characterized by the origins of food production through the development of animal and plant husbandry. There is indirect evidence that the sheep was domesticated in the Middle East about 9000 BC. Over the next three millennia wild cereal plants were domesticated, animal and plant husbandry were further developed, and small farming communities were formed (often in upland areas, where rainfall was adequate). Cultivation was accomplished with the use of the digging stick and the wood hoe. The Paleolithic division of labor persisted into the Neolithic Period, with men tending herds of animals and women managing garden plots. Late Neolithic stone tools were improved by polishing, and polished stone axes were used to prepare forest clearings for cultivation. Modern tests with Neolithic axes have demonstrated their remarkable effectiveness in the felling of trees. Neolithic crafts included pottery, spinning and weaving, basketmaking, and house building. The discovery of Neolithic artifacts on islands in the Mediterranean also testified to the early use of boats. AGRICULTURAL CIVILIZATION The invention that marked the beginning of agricultural civilization was the ox-drawn plow. It originated in the Middle East in the 4th millennium BC. Although the circumstances of its invention are unknown, the early scratch plow (or ard) was probably derived through modifications of the Neolithic adze and the hoe. Because traction was supplied by oxen, the provinces of animal husbandry and plant cultivation were merged, and the dual economy that had originated in the Paleolithic was now replaced by an economy of field cultivation. Combined with the techniques of fallowing, irrigation, and flood control that date from the same period, plow agriculture was successfully established in the rain-sparse river valleys of Mesopotamia, Egypt, and India, and the breakthrough to civilization was accomplished. Plow agriculture was accompanied by an array of momentous developments. Writing evolved; the political state came into being (possibly through the conflicting pressures of expanding population and limited fertile land in the river valleys); chronic warfare set in; and copper and bronze metallurgy was devised. Bronze Age The earliest phase of agricultural civilization is commonly known as the \TBronze Age\t. The use of copper and bronze (an alloy of copper and tin) gave rise to a variety of techniques and devices and to a complex of skilled artisans. Copper ores had to be mined and tin ores collected, often from distant sources, thereby encouraging commerce, cultural intercourse, and sometimes conquest; furnaces, crucibles, and fuels had to be provided for the smelting of the ores; and intricate molds, often made of several pieces, had to be prepared for the casting of the metal. Copper and bronze hand weapons came into use, but by far the most important innovation in military technology during the Bronze Age was the horse-drawn two-wheeled chariot. Although cumbersome two- and four-wheeled carts had been invented earlier, the highly mobile war chariot carrying an archer armed with the short, compound bow revolutionized military tactics after 1700 BC. Building technology also developed rapidly during the Bronze Age and, in the form of pyramidal structures, reached monumental proportions. In Mesopotamia molded, kiln-dried bricks were the favored building material for large structures, whereas in Egypt the famous pyramids were commonly built of limestone blocks. After this limestone was quarried with wooden, stone, and copper tools, the blocks were transported to the building site by barges and sledges. Methods of construction and the achievement of structural stability, however (rather than the quarrying and transportation of materials), presented the most formidable problems that Bronze Age builders succeeded in solving. The substantial technical and cultural progress of these early civilizations, the emergence of crafts whose practitioners were relieved of the need to participate in food production, the increase in population, and the rise of many urban societies centered in impressively wealthy cities were entirely based on the productivity, and hence on the food surpluses, of plow agriculture. At first, surpluses adequate to sustain civilization were possible only on irrigated land, so that the earliest civilizations were confined to alluvial river valleys. As the technology of plow agriculture improved, civilization spread to rain-fed lands away from the river valleys. Iron Age By the end of the 2d millennium BC iron metallurgy was developed, and a new technical era began. About 1000 BC an \TIron Age\t civilization arose in Greece that was based on rain-watered agriculture and used the implements of the new metallurgy. The production of wrought iron called for a technology fundamentally different from that of either copper or bronze. Higher furnace temperatures were required, and the iron emerged from the furnace as a red-hot, pasty ball that had to be worked by hammering, rather than as liquid metal that could be poured from crucibles into molds. Bronze and iron found their widest use in the paraphernalia of war. Hoplites (from the Greek hoplon, a round shield)--ranks of drilled infantry armored with helmets, corselets, greaves, and shields and armed with iron-tipped spears--became the backbone of Greek military power. The geographical position of Greece in the Mediterranean encouraged the development of ocean-borne commerce, and the Greeks built and maintained a large fleet of merchant ships and men-of-war. Greek building technology provided the technical basis for a notable architecture (see \TGreek architecture\t). Although the arch had been invented long before, Greek builders, using stone as their material, confined themselves to the post-and-lintel (column-and-beam) structural mode. To enable stone beams to resist cracking at their lower surfaces (where they are stretched), they were necessarily of massive size, with short spans, and rested on many columns. On occasion the Greek builders embedded wrought-iron bars in grooves formed in the beams to keep the tension in the stone within an acceptable range. The Greeks coined the term architekton to describe the practitioners of the fields encompassed in modern times by the disciplines of engineering and architecture--building, tunneling, mining, and hydraulic projects. Later, during the period of Greek imperialism (336-323 BC) under Alexander the Great, the architekton was engaged in the design and construction of the catapult, with which Alexander supplied his armies. In general, Greek technology remained independent of the scientific tradition that Greek natural philosophers were creating. Between 250 BC and AD 100, however, a school of scientist-engineers flourished at Alexandria and produced treatises on mechanical and pneumatic devices that display an interest both in the philosophy of nature and in the application of empirical formulas to engineering design. Roman and Medieval Innovations The skill of Roman engineers is legendary. In the art of building they mastered the technique of the stone arch and its variations in the vault and the dome (see \Tarch and vault\t; \TRoman art and architecture\t). In contrast to the post-and-lintel method, buildings employing arches primarily produce compressive forces and thereby improve the efficiency of stone, which is desperately weak under tension. Characteristically, the stone arch is composed of wedge-shaped blocks that must be supported during the construction process, generally by a temporary wooden scaffold, until the arch is complete. Once the arch is complete, the wedges are in equilibrium, provided that the horizontal thrust is resisted either externally by buttresses or internally by a tie-bar across the opening. The same principle was adapted to the construction of vaults and domes. The accomplishments of Roman engineers are best illustrated by their refinement of \Taqueduct\t design, in which they combine elements of bridge building, road making, tunneling, pressure piping, and reservoir construction. The flowering of agricultural civilization in Europe north of Rome during the Middle Ages was foreshadowed by Roman technical innovations. Roman engineers were familiar with the principle of the \Twaterwheel\t and its associated gearing as early as the 1st century BC, and they occasionally employed it in the construction of \TMills\t. Even more important was the development of a heavy \Tplow\t capable of turning the clay soils of northern Europe. The ancient light plow drawn by a pair of oxen was effective in the dry climates of the Middle East and the Mediterranean world, where the soils were light and friable. In northern Italy and in transalpine Europe the light plow permitted tillage only on well-drained upland soils, whereas the wet, cohesive soils of the vast lowlands and the north European plain could not be cultivated. The heavy plow with its vertical coulter, horizontal plowshare, and moldboard to turn the soil, mounted on wheels and drawn by teams of four, six, or eight animals yoked in pairs, made possible the civilization of northern Europe. During Roman times a coulter was sometimes used, and the light plow was occasionally mounted on wheels; development was slow, however, and it was only in the 9th and 10th centuries that the fully developed heavy plow came widely into use and began to transform Europe. Extensive tracts of fertile land were opened to cultivation. The depth of the cut made by the heavy plow and the overturning of the sod increased fertility, and elimination of the need for cross-plowing increased productivity. As the heavy plow began to transform European agriculture, property relations and social patterns also began to change. The square tracts characteristic of light-plow cultivation (because the fields were cross-plowed) gave way to elongated tracts (the "long acre"), on which the heavy plow would not have to be turned around as often. Peasants found it necessary to pool their resources in order to form the teams of oxen required to pull a heavy plow. The heavy plow and communal tillage became the basis of the manorial system, which provided medieval Europe with food surpluses, an increasing number of skilled artisans removed from the web of food production, and a growing population. About the same time, the introduction of the \Thorseshoe\t and the horse collar permitted the substitution of the horse, with its greater speed and endurance, for the ox, completing the agricultural revolution that the heavy plow had initiated. The Middle Ages in Europe were in general prodigiously innovative. In the 8th century iron became widely available and once again was adapted to military needs. Heavy cavalry, its lance-bearing riders armored with wrought iron and stabilized by \Tsaddle\t and \Lstirrup\ls, became the shock troops of medieval Europe. In the 12th century water mills, which had not been widely used until then, and windmills, the concept of which was only then reaching Europe from the East, brought a revolution in the production of power (see WINDMILLS AND WIND \Tpower\t). At first both devices were used mainly in corn mills, but the windmill soon acquired its characteristic role as a water-pumping engine, and the waterwheel was adapted to a variety of enterprises including sawmills, hammer mills, and stamping mills. The application of waterpower to the bellows of the blast furnace made possible for the first time the production of large quantities of cast iron. The technical and cultural progress of the late Middle Ages is most vividly exemplified by \TGothic\t \Tarchitecture\t. The urbanization of Europe was accompanied by waves of \Tcathedral\t building, and in the 12th century builders introduced a series of innovations that enabled them to achieve structural lightness while carrying their vaults to extreme heights and admitting substantially more light through large expanses of glass windows. The flying \Tbuttress\t, calculated to resist the thrust of the central vaults, became a hallmark of these lofty structures, which, within a century, achieved vault heights of 49 m (160 ft). The master masons who designed these remarkable buildings proceeded without the insights of science, basing their specifications only on experience, rules of thumb, intuition, and daring. Medieval Europe's inventive impulse contained the seeds of both the reformation of medieval society and the achievement of European influence throughout the world. During the 14th century \Tfirearms\t appeared in Europe. Early guns were made either of wrought-iron strips hooped together to form the barrel or of cast brass or bronze. Ironically, the bell-founders, who had refined their technique in the casting of church \Tbells\t, now turned to the casting of \Lcannon\ls. The craft of the gunsmith came into being, and national arsenals were established. Before the middle of the 16th century, English founders had perfected the casting of iron, instead of bronze, guns, thereby sharply reducing the cost of ordnance. The medieval castle was an easy target for the new \Tweapons\t, and, along with large catapults, the castle passed from the scene. New \Lfortification\ls were now required--polygonal and star-shaped--to increase the length of ramparts on which guns could be mounted and to present unfavorable shot-deflection angles to attacking gunners. Hand guns were also rapidly developed, and by the end of the 16th century they had swept the long-bow from the field. The \Tmusket\t in particular made infantry once again the most decisive force on the battlefield. Parallel with these developments in land warfare, the sailing \Tship\t was being transformed into a formidable instrument of naval power, world exploration, and commerce. In the 15th century the carrack appeared--full-rigged, more manageable than earlier sailing ships, and capable of ocean voyaging. Armed with hundreds of iron and brass guns, carracks of more than 1,000 tons served as both merchantmen and men-of-war. In the second half of the 16th century the galleon was developed primarily as a fighting ship. The \Tgalleon\t showed most of its guns through ports cut in the hull, and its handling was improved over that of earlier ships by increasing the length-to-breadth ratio of the hull and by reducing the size of the forecastle and the afterdeck. The Renaissance From the 15th through the 17th century, the period designated by cultural historians as the Renaissance, the new warfare employing guns and armed ships changed Europe from a provincial region to a center of world power. The New World was explored and conquered, and commerce with the East--carried on by armed merchantmen--grew increasingly profitable. European cultural life flourished, abetted by the appearance of the printed book (see \Tprinting\t) during the 15th century. Additionally, in turn, the widening interest in technology and industry was reflected in the publication of richly illustrated technical treatises. The new technology produced new problems, partly as a result of the increased use of iron in the making of cast-iron ordnance. Because the blast furnace was charged with ore and fuel in intimate contact, attempts to use coal as the fuel invariably failed because the impurities that it contained were absorbed by the iron. It was thus necessary to charge the blast furnace with charcoal (derived from wood) as the fuel, and by the end of the 16th century the iron industry was consuming timber at a prodigious rate. Combined with the demands of \Tshipbuilding\t (the largest ships of the time each required several thousand trees in their construction), the iron industry was rapidly deforesting Europe. The "timber famine" was most severely evident in the British Isles, where the making of both guns and ships was booming. Shortly afterward a second problem arose, this one in the mining industry. As mines were sunk to ever greater depths in search of minerals, the shafts filled with groundwater and had to be constantly pumped. A variety of devices were employed, including the suction pump, which was powered by the draft of animals at the pit-head. By the end of the 17th century, however, it became evident that more-powerful engines would be needed. INDUSTRIAL CIVILIZATION: EIGHTEENTH CENTURY Both the problem of high consumption of timber in the smelting of iron ore and the problem of flooding in deep mines received technical solutions early in the 18th century. These solutions, both of which were reached in Great Britain, where the problems were most sharply felt, set the stage for the Industrial Revolution. In 1709 the ironmaster Abraham \TDarby\t I succeeded in producing sound cast iron in a blast furnace charged with iron ore and coal (and soon afterward with coke, derived from coal). In 1712 another Englishman engaged in the iron trade, Thomas \TNewcomen\t, invented the \Tsteam engine\t for the purpose of driving the pumps used in clearing groundwater from mine shafts. By the end of the 18th century the British iron industry had largely replaced charcoal with coke. Within a short time, too, Newcomen engines were serving most of the larger collieries in Great Britain, making possible the opening of new mines that otherwise would have been unworkable. These two innovations, the steam engine and the making of iron with coal, not only broke critical bottlenecks that were constraining economic progress, but also produced an interlocked complex of industrial development: the steam engine promoted coal production by clearing flooded mine shafts; coal (in the form of coke) revived the iron industry, which had begun to slump as a result of the timber famine; iron was used in the further production of steam engines, and this in turn demanded improved metalworking techniques. In the 1760s, James \Twatt\t increased the efficiency of the Newcomen engine by providing it with a separate condenser, thereby obviating the need alternately to heat and cool the cylinder and piston. Watt followed this important invention with a remarkable series of additional contributions: "sun-and-planet" gearing to translate the reciprocating motion of the steam engine into rotary motion for operating mills; the double-acting steam engine and the "parallel motion" used to connect its rigid piston rods to the overhead beam without causing the rods to wobble; the principle of steam cutoff, whereby Watt recognized that because of its expansive power steam need not be admitted into the cylinder during the entire stroke; and an indicator for determining the pressure in the cylinder during the cycle. John \TWilkinson\t designed a boring machine that radically improved the accuracy with which steam-engine cylinders could be bored; the steam engine was combined with cast-iron blowing cylinders to produce a more powerful draft in the blast furnace than the older bellows could provide; and by the beginning of the 19th century the compact, high-pressure steam engine (in contrast with the Newcomen and Watt engines, which relied on atmospheric pressure) was invented, opening the way to the construction of steamboats and steam locomotives. This web of technical innovation is characteristic of the Industrial Revolution. It may be seen as well in the \Ltextile industr\lies, where \Tspinning\t and \Tweaving\t machinery were alternately improved in a pattern of reciprocating challenge and response. The application of steam power further stimulated the concentration of industry in mills and factories and, where it replaced the waterwheel, steam power released industry from its need to be near rural waterpower sites. Cities became the hubs of industrial growth and the centers to which waves of agrarian population migrated as industrial civilization took hold. Agriculture, too, was changing (see \Tagriculture, history of\t), and some of the changes furthered the exodus of farmers from the land. The tradition of communal pastures increasingly gave way to enclosed fields, which promoted agriculture by permitting continuous cropping and by improving stock-raising: more fodder could be produced, and the promiscuous breeding of livestock could be prevented. Moreover, during the century following 1750, industry directly affected agriculture by manufacturing new implements and new machines. Many wooden and wrought-iron tools fashioned by local artisans were replaced by cast-iron tools produced in factories. Mechanical devices, some even steam-powered, were introduced for reaping, threshing, and plowing. Iron also changed the landscape as the introduction of structural iron altered the mode of building. Stone had been a hallmark of monumental building throughout the time of agricultural civilization. Public buildings were generally made of stone, and stone-arch bridges dotted the landscape. In the last quarter of the 18th century, however, British ironmasters found a new use for cast iron (which, like stone, is strong in compression and weak in tension) when they succeeded in casting the components of the arch bridge. Early in the 19th century the introduction of structural \Twrought iron\t made possible the large suspension bridge, and by 1850 the wrought-iron tubular bridge for carrying railroads made its appearance. If the engineer was instrumental in making the Industrial Revolution, it can equally be said that the Industrial Revolution gave rise to the \Tengineering\t profession as it is recognized today. Where previously engineers had risen through the ranks of craftsmen, in the 18th century it was becoming apparent that the act of design could be codified in the form of technical training, and the military services began to seek such training for their officer corps. In the 1740s the British government established a military academy at Woolwich at which cadets were instructed in the application of elementary mathematics and statics to gunnery and the design of fortifications. Later in the century John \TSmeaton\t coined the term "civil engineer" to distinguish civilian engineers from the increasing number of military engineers being graduated from Woolwich. A short-lived fraternity that called itself the Society of Civil Engineers (the "Smeatonians") formed around Smeaton; the first true professional organization in the field of engineering, however, was the Institution of Civil Engineers, founded in London in 1818. Technical studies penetrated the established universities slowly, and it was in new institutions--such as the Ecole Polytechnique in Paris and the University of London--that engineering first took root in university education. Harold Dorn INDUSTRIAL CIVILIZATION: NINETEENTH CENTURY Power The basic source of converting energy into power during the 19th century was James Watt's double-acting \Tsteam engine\t. High-pressure steam for steam-run, or "horseless," carriages was developed by Richard \TTrevithick\t in England (1802) and Oliver \TEvans\t in the United States (1805). Through most of the 19th century waterpower was the principal competitor of steam, and its use was markedly stimulated by the water turbine, developed (1827) in France by Benoit Fourneyron. By the end of the century the steam \Tturbine\t was introduced by Carl Gustav de Laval in Sweden (1882) and Sir Charles Algernon \TParsons\t in Great Britain (1884), but its application was delayed until the 20th century. Experiments with the \Tinternal-combustion engine\t began early in the century but without success until Jean Joseph Etienne \TLenoir\t built an operational if inefficient two-cycle engine (1860) and the first \Tautomobile\t with this type of engine in 1862. The critical breakthrough in designing an efficient internal-combustion engine came in 1876, when Nikolaus August \TOtto\t marketed the "Silent Otto" gas engine, having four cycles: intake, compression, stroke, and exhaust. In the 1880s the engine was adopted by Karl \TBenz\t and Gottlieb \TDaimler\t to power motor vehicles. Rudolf \TDiesel\t's engine, in which combustion is produced by high pressure in the cylinder, was exhibited in 1897. Electric power became possible with the nearly simultaneous discovery (1831) of electromagnetic induction by Michael Faraday (England) and Joseph Henry (United States), but its application required the development of a practical dynamo and electric motor. The dynamo evolved in a series of steps, beginning with the first one built (1855 patent), by Soren Hjorth of Denmark. Simultaneously, experiments in electric lighting (see \Tlighting devices\t) culminated with Thomas A. \TEdison\t's invention of the incandescent lamp in 1879. Edison opened (1882) the first direct-current central generating station, on Pearl Street in New York City. Frank J. \TSprague\t produced a successful direct-current electric motor in 1884 and applied it in 1887 to a street-trolley railway in Richmond, Va. Immediately afterward Nikola \TTesla\t, a Hungarian immigrant to the United States, developed (1888) the first successful alternating-current induction motor. Industry The \TIndustrial Revolution\t, which began in Great Britain in the 18th century, spread to the rest of western Europe and North America during the 19th century. The pattern of diffusion was quite uniform, beginning with textiles, coal, and iron. In textiles such improvements as the Jacquard \Tloom\t (France, 1801) were developed, which allowed fabrics with woven patterns to be produced cheaply. The \Tsewing machine\t was invented (1846) in the United States by Elias \THowe\t and mass-marketed (1851) by Isaac Merrit \TSinger\t. Iron was the basic metal of industry until after the discovery by Henry \TBessemer\t (British patent, 1856) and William Kelly (U.S. patent, 1847) of a process for making large amounts of steel cheaply (see \Tiron and steel industry\t). The superior Siemens-Martin open-hearth process for making high-quality steel was first demonstrated in France in 1863. Once steel was more readily available, it became an important material for construction (see \Tbuilding construction\t), notably in the American \Tskyscraper\t and in bridges (see \Tbridge\t, engineering). It made possible heavier railroad equipment and replaced iron in shipbuilding--iron ships themselves were an innovation of the mid-19th century. Steel also influenced warfare by permitting high-powered, long-range weapons and more-efficient armor to be designed. An equally important development was increased mechanization. In 1807, Robert \TFulton\t designed the first practical steamboat, the \TClermont\t, using James Watt's steam engine. \Lsteamboat\ls were restricted at first to inland coastal waters--until more fuel-efficient engines were designed in order to make ocean voyages practical. The steam railway is considered to have begun (1825) in England with the Stockton and Darlington Railway, but the first convincing demonstration of the steam \Tlocomotive\t was George Stephenson's \TRocket\t on the Liverpool and Manchester Railway in 1829 (see \Trailroad\t). Rail transportation spread rapidly, competing with the elaborate \Tcanal\t systems, built during the same time, as an economical method of inland transportation. The mechanization of agriculture began with Cyrus McCORMICK's \Treaper\t (1831) in the United States. New industries also appeared. The \Tchemical industry\t was revolutionized by the \TSolvay process\t for making alkalis (Belgium, 1872) and the development of the first plastic celluloid (United States, 1861) and of coal-tar dyes (England, 1856). Charles \TGoodyear\t made \Trubber\t (United States, 1839) usable, and \Taluminum\t came into industrial use with the Hall-Heroult electrolytic process (United States-France, 1886). The \Tpetroleum industry\t was born in 1859, when Edwin L. \TDrake\t sank an oil well in Titusville, Pa. The industry's major product during the 19th century was kerosene for illumination. The \Ttelegraph\t, perfected (United States, 1837) by Samuel F. B. \TMorse\t and his assistant Alfred Vail, and the \Ttelephone\t, invented (United States, 1876) by Alexander Graham \Tbell\t, fostered communications industries based on electricity. INDUSTRIAL CIVILIZATION: TWENTIETH CENTURY Before 1945 The technological and industrial expansion of the 19th century continued unabated during the 20th century. Geographically, industrialization spread into eastern Europe, specifically Russia, and into Japan. Motor-vehicle manufacturing grew to an enormous scale (see \Tautomotive industry\t), especially after Henry \TFord\t's adoption (1913) of \Tmass production\t by the moving \Tassembly line\t. Mass production and the proliferating use of automobiles created a demand for gasoline that stimulated worldwide exploration for oil as well as research in oil-refining techniques. In addition, oil to a great degree replaced coal as a fuel. Another effect of the automobile was extensive highway construction (see \Troads and highways\t). \Taviation\t is a 20th-century phenomenon, beginning with the invention (1903) of the airplane by the Wright brothers (see \TWright, Orville and Wilbur\t). Constant improvements in airframe design and engines made military aviation (see \Taircraft, military\t) a dominant feature of warfare by 1945, and commercial aviation had \Taircraft\t capable of transatlantic travel by the same year. Lighter-than-air craft (see \Tairship\t) were developed by the German Ferdinand, Graf von \TZeppelin\t, and had potential for both military and commercial use, but a series of disasters--notably the burning (1937) of the \THindenburg\t--destroyed confidence in them. Communications was transformed by Guglielmo \TMarconi\t's invention of \Tradio\t in 1896 and by the subsequent discovery of the vacuum tube. Radio quickly became indispensable for maritime and military communication and it also generated an extensive entertainment industry during the 1920s. The moving-picture industry also developed at that time (see \Tfilm, history of\t). Experiments with \Ttelevision\t achieved success in the 1930s, but commercial application was delayed until after World War II. In the chemical industry further developments occurred in \Tplastics\t and \Tsynthetic fibers\t. \Tnylon\t was discovered by Wallace H. Carothers at Du Pont in 1927 and was manufactured by 1939. In agricultural technology, farm mechanization progressed with the adoption both of steam power and then of the internal-combustion engine for farm machinery. Research in genetics and soil chemistry led to the development of hybrid corn and other disease-resistant crops. Other innovations included the introduction of the Rust cotton picker in 1939 and chemical \Lfertilizer\ls and \Tpesticides\t. Technological advance influenced and was influenced by the wars of the 20th century. During World War I there occurred the first general use of long-range \Tartillery\t, \Lmachine gun\ls, \Tpoison gas\t, \Lsubmarine\ls, \Ltorpedo\les, tanks (see \Tarmored vehicle\t), aircraft, and radio. World War II introduced \Laircraft carrier\ls, \Tradar\t, \Tsonar\t, ballistic missiles, and, above all, the \Tatomic bomb\t. The jet engine (see \Tjet propulsion\t) had been experimented with before World War II by Sir Frank Whittle (Great Britain, 1930) and Hans von Ohain (Germany, 1935); the Germans had a few jet fighters in operation toward the end of the war. Since 1945 In the years since World War II, technological advance accelerated. \Tnuclear energy\t has been used successfully in large warships. More important, nuclear power permits submarines to stay submerged for long periods. Commercially, nuclear energy has been used in generating electric power. Its progress has been retarded, however, by fear of its possible hazards. Electrical and electronic engineering underwent a revolution with the invention (1948) of the transistor at the Bell Telephone Laboratories by John \TBardeen\t, Walter \TBrattain\t, and William \TShockley\t. It replaced the vacuum tube and permitted elaborate circuitry in extremely small spaces. The transistor made possible the development of \Tcomputers\t and automatic controls. The first electronic computer, \TENIAC\t (see \TENIAC\t), a large machine that used vacuum tubes, was built by John Presper \TEckert\t and John W. \TMauchly\t and put into operation in 1946. In the 1950s the \Tlaser\t AND \Tmaser\t (Light and Microwave Amplification by Stimulated Emission of Radiation) were developed. In medicine, \Tantibiotics\t were first used extensively during World War II. A major event was the discovery of an effective antipolio vaccine by Dr. Jonas \TSalk\t (United States, 1954). In addition, \Torgan\t TRANSPLANTS (heart and kidney) began to be done more frequently. The most spectacular technological achievement of this period has been in \Tspace exploration\t. It began with experiments in rocketry and missile development (see \Trockets and missiles\t) during World War II and reached fruition with the launching of the Soviet Union's Sputnik 1 (see \TSputnik\t)--the first space satellite (see \Tsatellite, artificial\t)--in October 1957. The United States, after extensive preparation, achieved a landing on the Moon on July 20, 1969 (see \TApollo program\t). Mercury, Venus, Mars, Jupiter, Saturn, and Uranus, as of 1986, have been investigated at close range by unmanned spacecraft. \Lcommunications satellite\ls have greatly facilitated transmission of telephone, radio, and television signals. The current manned space effort has been focused on \Tspace\t \Tstations\t and the \TSpace Shuttle\t. John B. Rae Bibliography: Adas, Michael, Machines as the Measure of Man: Science, Technology, and Ideologies of Western Dominance (1989); Bernal, John Desmond, Science and Industry in the Nineteenth Century (1970); Derry, Thomas K., and Williams, Trevor I., A Short History of Technology (1961); Ferguson, Eugene S., Bibliography of the History of Technology (1968); Hardison, O. B., Jr., Disappearing through the Skylight: Culture and Technology in the Twentieth Century (1990); Hindle, Brooke, Technology in Early America (1968); Hodges, Henry, Technology in the Ancient World (1970); Hughes, Thomas P., ed., Changing Attitudes toward American Technology (1975); Klemm, Friedrich, A History of Western Technology (1964); Kranzberg, Melvin, and Pursell, Carroll W., Jr., eds., Technology in Western Civilization (1967); Mumford, Lewis, Technics and Civilization (1934); Needham, Joseph, Science and Civilization in China, 5 vols. (1954- ), and The Shorter Science and Civilisation in China, vol. 1, ed. by Colin A. Roman (1978); Pursell, Carroll W., ed., Readings in Technology and American Life (1969); Singer, Charles, et al., eds., A History of Technology, 5 vols. (1954-58); White, Lynn, Medieval Technology and Social Change (1962). See also: separate entries on the industries and technologies discussed.