Science & inventions
radar (radio detection and ranging), a device for remotely determining the direction, range, or presence of objects using radio waves. It is used in air-traffic control, for navigation by ships, aircraft, and some missiles, and in warning and detection systems. It provides a means of detecting objects over quite long distances or when visibility is poor. The principle of radar was first discovered in 1904 by the Austrian Karl Hulsmeier. In 1935 R. M. Page in the USA constructed a radar device that was used to determine the positions of aircraft. A comprehensive radar system, then called radio direction finding (RDF), was developed independently in the UK from 1935 by Watson-Watt and others. The invention in 1939 of the magnetron, a thermionic valve capable of producing pulsed radio waves of very high (microwave) frequencies, made radar a practical proposition, and it played a decisive role in World War II. From 1945 radar became commercially available.
Radar measures the distance of an object from a radar transmitter by timing the interval between the transmission of a pulse of radio waves and the reception of the echo of the pulse from the object. The distance can be calculated from the time interval because the speed of the radio waves (the speed of light) is known. The pulses of radio waves are usually directed in a narrow beam from the transmitting antenna, enabling the bearing of the object to be determined. Usually, the radar antenna rotates continuously, so that the radar beam is scanned through 360 degrees. The positions of objects detected by the radar are normally displayed on a plan position indicator (PPI), in which the radar transmitter is at the centre of the screen, and the objects detected appear as bright spots or areas of light. The position of the object on the screen corresponds to its position in space. Another form of radar is secondary radar, in which the reception of a radar pulse at the target object triggers another pulse from a transmitter carried by the target (usually a ship or aeroplane). Secondary radar can be used over a longer range than normal radar, and information about the target object can be obtained from the triggered pulse.
robotics, the science and technology of machines designed to function in place of a human being, especially to carry out tasks automatically. The term robot (from the Czech robota, 'compulsory service') was coined by the playwright Karel Capek in 1920. Practical robotics was first formulated by the British inventor C. W. Kenward in 1957, and subsequently exploited in the USA for industrial automation to handle parts for die casting, injection moulding, and metal-cutting machines. A robot which could manipulate a tool (for painting) was first used in Norway in 1966, and in the USA, robots were developed for spot-welding on assembly lines. Since then, there has been a continual evolution towards robots of greater precision, such as the Japanese selective compliance assembly robot arm (SCARA).
A modern robot has a mechanical manipulator (usually an arm) and sensors, controlled by a computer. Early hydraulically powered robots have given way to direct-drive machines using electric motors. The main goal of robot research in artificial intelligence is to enable robots to sense and move intelligently around their environment.
space-plane, a one-stage vehicle capable of carrying a crew or cargo into space and landing back on Earth. The US Space Shuttle and others under development, including the Soviet 'shuttle' and the European Hermes, are not real space-planes because they require rocket launchers. Preliminary design work on space-planes, with engines capable of both atmospheric flight and space-flight, has been carried out in the USA (the X-30), the UK (HOTOL), Germany (the Sanger space-plane), and Japan (HOPE).
aeroplane (US, airplane), a power-driven, heavier-than-air aircraft with fixed wings. Aeroplanes vary enormously in size, performance, and function, from single-engined sport planes to large airliners or supersonic fighter aircraft. Before the 1930s aeroplanes had wooden, wire-braced airframes covered by fabric, but modern aircraft are constructed as a shell of thin metal sheeting strengthened by ribs and longitudinal members. The commonest aircraft structural materials are aluminium alloys, which are cheap, strong, and fairly light. Alloys of titanium, and composite materials such as fibre-reinforced plastics, are increasingly used for structural components because of their lightness.
The basic components of an aeroplane are the fuselage, wings, engines, tail assembly (empennage), and undercarriage. The fuselage carries the passengers, crew, and cargo. The shape of the fuselage relates to the aircraft's operating speed. Low-speed aircraft have little streamlining, while the shapes of high-speed subsonic and supersonic aircraft are shaped to minimize drag at normal operating speeds. Most modern aeroplanes are monoplanes, with only one pair of wings. Wing shape varies with function. Most aeroplanes are powered by combinations of a piston engine and propellers, by turboprops, or by turbojet engines (see jet engine). In single-engined aircraft the engine is mounted in the fuselage, while multiple engines may be mounted on the wings, fuselage, or tail. The tail unit consists of a horizontal stabilizer, usually projecting from the mid-line of the rear fuselage, and a vertical tail fin. In the T-tail configuration, the horizontal stabilizer is placed at the top of the fin: this configuration is often used when engines are part of the tail structure. Pneumatic-tyred undercarriages are fitted on virtually all modern aeroplanes. On older aircraft, and on some light aircraft today, the main wheels are located well forward, with a smaller wheel or skid on the tail, but most aeroplanes now use a 'tricycle' undercarriage, with the main wheels behind the centre of gravity and a smaller wheel at the nose. Undercarriages are often retractable, as this greatly improves flight performance. Aeroplane controls comprise a control column or wheel for operating ailerons and elevators, a rudder bar moved by the feet, and the engine ignition and throttle. In addition to this basic array there may be many other controls and instruments. Computers are often used to monitor aircraft functions, or actually to control the aeroplane.
cathode, the negative electrode of a thermionic valve, cathode-ray tube, battery, or electrolytic cell. The cathode is the electrode by which electrons enter a system: they are emitted by, or flow from, the cathode. In electrolysis cations gain electrons at the cathode
radio, the transmission of information by means of electromagnetic radiation in the frequency range 3 kHz to 40,000 MHz, wavelength range 1 cm to more than 1 km (0.4 inch to 0.6 mile). The radio-frequency spectrum is arbitrarily divided into a number of wavebands, from very low frequencies (long wavelengths) to ultra-high and microwave frequencies (short wavelengths). Sections of the spectrum have been allocated by international agreement to use for telegraph, telephonic speech, and radio and television broadcasting. In order to be transmitted, the information in a radio signal is used to modulate a radio-frequency wave. The modulated radio signal is then amplified, and a transmitting antenna projects as much as possible of the radio-frequency energy into space. The signals are picked up by the aerial of a radio receiver tuned in to the wavelength of the transmission. In 1864 the British physicist James Clerk Maxwell predicted the existence of electromagnetic radiation and its ability to travel through space at the speed of light. Hertz confirmed Maxwell's theories experimentally in 1888, but it was Marconi who developed these discoveries to provide a means of communication. In 1896 he transmitted a radio signal from Penarth to Weston-super-Mare, UK; in 1901 he transmitted the letter 's' in Morse code across the Atlantic from Poldhu in Cornwall, UK, to St Johns, Newfoundland, Canada, using a large antenna supported by two 60-m (200-foot) towers.
Marconi's broadcasts were telegraphic signals rather than sound transmissions. Early in the 20th century Reginald Fessenden developed amplitude modulation, which made it possible to transmit sound by radio. In 1906 he made a music transmission that was picked up by several wireless operators and was claimed as the first radio broadcast. These innovations led to the development of simple crystal radio receivers after World War I. By 1921 regular programmes were being transmitted from eight stations in the USA; the BBC was transmitting in the UK by 1923, and by 1925 there were 600 radio stations world-wide. Radio soon became ubiquitous, offering entertainment and instruction, news and advertising; innovations included soap operas and quiz shows.
Because radio frequencies are widely used in communications by aircraft, ships, police, and for all the messages carried by satellite transmission, as well as by broadcasting services, access to them is regulated by national agencies, such as the Federal Communications Commission in the USA, and by the International Telecommunications Union, a specialized agency of the UN. In the USA, commercial radio is financed by advertising, and control is minimal apart from allocation of wavelengths to stations. Most other governments exercise greater control, and some encourage public service broadcasting. Short-wave radio broadcasting spread during World War II for news and armed forces networks. After television supplanted radio as the chief broadcasting medium, some stations began to target more local or specialist interest audiences (see narrowcasting). Chat shows, phone-ins, and disc-jockeys came to greater prominence. Radio sets became portable with the development of the transistor in 1948 and still smaller with the introduction of integrated circuits. The number of stations and receiving sets has continued to multiply: in the late 1980s there was one set per six persons in developing countries compared with over one set per person in the industrialized world. Community stations have been set up in response to demands for citizens' access, notably in Europe. In Japan local mini-stations broadcast up to a distance of half a mile. As the number of radio-frequency users has increased, higher radio-frequencies have been exploited. The future of radio lies largely in its potential for developing countries and in new technologies such as microwave satellite communication. These developments raise the same questions of access and control voiced by earlier generations of amateur radio 'hams' and by enthusiasts for citizen's band (CB) radio, which was deregulated in the USA in 1983 and subsequently in other countries.
cathode-ray tube (CRT), a funnel-shaped electron tube that converts electrical signals into a visible form that can be displayed on a screen. CRTs are used widely in television receivers, visual display units for computers, and in displays for oscilloscopes. They consist primarily of an electron beam traversing the length of the tube, the intensity of which varies according to an input signal containing the visual information to be displayed. Acting on this electron beam are several sets of electrodes and magnetic coils, which together confine and direct the beam and enable it to be moved back and forth across (scan) a phosphor coat on the back of the screen inside the tube. When the electron beam strikes the phosphor, a light spot is produced, the intensity of which is proportional to the intensity of the beam. As the beam scans the screen, a full screen display is formed.
television, a system for converting visual images (and accompanying sound) into an electrical signal that can be transmitted, either through an electrical cable or on a radio waveband, to receivers that reproduce the images on a screen. Transmission of all the visual and sound information of a moving scene through one electrical circuit or radio beam requires considerable processing; all the visual information in a scene cannot be transmitted simultaneously. Instead, the television camera electronically scans the scene and divides it into 300,000 or more elements, for each of which an electrical impulse, proportional to the amount of light in that area of the scene, is emitted. In order to depict rapid motion smoothly, twenty-five of these scans must be made each second; motion is simulated by a rapid succession of still scenes, as in a cine-camera. A television system must thus transmit more than four million electrical impulses per second in order to give a detailed, moving image on the television screen. For transmission, the television signal is modulated: a very large bandwidth is needed to transmit all the information from a moving picture. The transmitted signal is picked up by the household television antenna and reassembled in the television receiver, which reconstructs the images so quickly that the eye is unaware that they have been assembled sequentially.
The conversion of pictures into electrical impulses first became a possibility in 1873, when Willoughby Smith noted that the electrical resistance of selenium changed in proportion to the amount of light falling on it. A mechanical means of scanning a scene (the Nipkow disc) was developed in 1884, and in 1926 John Logie Baird used this mechanical system to demonstrate the first electrical transmission of moving pictures. Baird's demonstration stimulated research in the USA, the UK, the Soviet Union, and Germany. Already in 1923 Vladimir Zwyorkin had patented the iconoscope, an electronic scanning television camera that provided the basis for the modern camera. By 1935 Germany had a regular broadcasting service, though the picture quality was poor. In the UK, the BBC began broadcasting in 1927, using Baird's black-and-white mechanical system: in 1937 they began the world's first high-quality public television broadcasting service, using an electronic system developed by Alan Blumlein. In 1938 Baird developed a photo-mechanical colour television system, but colour broadcasts did not become viable until 1953, when a standardized electronic system compatible with existing black-and-white receivers was developed in the USA. This system, known as the NSTC system, is currently used in the USA and Japan. Elsewhere two other systems--SECAM (used in France and the Soviet Union) and PAL (used by most of Europe)--have been developed. More recent developments in television technology include the growth of cable television; the introduction of stereo sound; and satellite television, in which microwave transmissions are broadcast via communications satellites either directly to domestic satellite dishes, or to ground stations for relay via cable. The increased bandwidth of satellite and cable systems has led to tens of television channels often being available to viewers. New developments include high-definition television (HDTV) broadcasting, in which the television images are made up of over 1,000 scanning lines instead of the current 525 or 625, and the transmission of television pictures as digital rather than analog signals. Japanese analog HDTV (Hi-Vision) television receivers were first sold in 1990. (See also video recorder, videotex.)
Television has now become the most important of the entertainment mass media. In the 1950s it began to supplant cinema and radio in commercial importance and in the size of its audience. In the Americas, commercial television, financed by advertising, has always been dominant, but elsewhere state television is a significant component of services. Satellite services, like cable television, are paid for per view or by subscription. The 'global village' predicted by the Canadian communications theorist McLuhan in the 1960s is now a possibility. A single programme, such as the Live Aid pop concert for Ethiopian famine relief in 1985, can now reach hundreds of millions of people simultaneously in virtually every country of the world. The video recorder and use of the television receiver for broadcast database information have further extended television's uses. There were 477 sets per 1,000 people in industrial countries in 1986, but only 40 sets per 1,000 in the developing countries, some of which, such as India, had fewer than 10 sets per 1,000. This, however, understates the access people all over the world have to television. The ubiquity of television's images of the world about us have renewed debate about the cultural and political roles of broadcasting. The growing concentration of media ownership in the hands of a few companies has at times been at the expense of public service broadcasting. The concern of developing countries that television is an instrument of cultural imperialism has led to demands for a New World Information Order with re-apportionment of the radio spectrum, dominated as it is by the industrial countries. Domestic critics see television as responsible for declining social values, particularly by portraying violence in entertainment programmes. The influence of advertising on programme content is another area of controversy.
video camera, a camera for recording electronically encoded visual images. Video cameras for amateur use are designed to be used with video recorders. These can be either separate portable units or, more commonly, video-tape cassette recorders incorporated with the camera in devices known as camcorders. Video cameras are highly sophisticated, using the latest electronic technology to maximize ease of use. Recently, the still video camera was introduced, combining ordinary photography with electronic video technology. In both camcorders and still video cameras, the lens focuses images on to a charged-coupled device (CCD). The image is then recorded either on to videotape, or (for a still camera) on to a magnetic disk or compact disc, which acts as the 'film'. The videotape from a camcorder can be played back on a suitable television receiver. Still video images can also be replayed on a television receiver using a computer, or printed out as a hard copy 'photograph' without the need for chemical processing.
calculator, a device that performs arithmetical calculations. An early aid to calculation was the abacus, a bead frame still used in parts of the Arab world, Russia, South-East Asia and China. In the early 17th century, the British mathematician John Napier invented logarithmic tables. Soon afterwards, in 1624, the German mathematician Wilhelm Schickard built a calculating machine for the creation of astronomical tables, probably the first use of gears in a calculator. In 1642 Pascal devised the first automatic adding machine, used for accountancy calculations. This had gears which were turned and engaged during the adding process. The German philosopher and mathematician Gottfried Leibniz improved on Pascal's design, producing in 1671 a stepped-wheel machine to perform multiplication, the principles of which have been used in almost every subsequent mechanical calculator. Calculating machines remained isolated curiosities until the mid-19th century, when improved reliability led to their more general use.
The first half of the 20th century saw a great demand for adding machines, typically desk-top mechanical devices, hand-operated by a lever. Their calculations were based on addition, with multiplication, for example, being performed by repeated addition. Information was stored and sorted using punched cards. For more specialized work, engineers began to explore methods of programming desk calculators, research which ultimately led to the modern digital computer (see computer, history of). The calculating machine itself evolved into the present-day hand-held electronic calculator, in which a small number of integrated circuits replace the gears of the mechanical calculator. Data and commands are entered through a simple key-pad and are usually read from a seven-segment display. Numbers processed by electronic calculators usually have a 'floating point', that is, the position of the decimal point is automatically adjusted during each calculation. This means that a very wide range of numerical values can be processed. Frequently, a memory is used to store partial or temporary results. A programmable calculator resembles a simple computer system in that a complex program involving many calculation steps may be entered into memory and executed on different data each time the program is run.
ship, most commonly any large seagoing vessel, although the term ship can also refer to a type of rig, 'ship rig', describing the arrangement of sails on three- or four-masted ships of the 16th and 17th centuries, which were square-rigged on all but the rearmost (mizen) mast. The earliest seagoing vessels were probably used about 60,000 years ago by the earliest colonizers of Australia. Their craft were probably canoes or rafts, propelled by paddles. Later, oars and then sails were developed. With the advent of sail power, sailing ships became the predominant form of power at sea, and remained so until the mid-19th century. Steamships were developed throughout the 19th century, and in the 20th century motor ships were introduced, generally powered by diesel engines. Until the 19th century most ships were built of wood, but in 1839 the development of techniques of using magnetic compasses in iron-hulled ships made seagoing iron ships possible. The use of iron, and later steel, for shipbuilding led to changes in hull design and growth in ship size.
Modern ships are usually built of steel, though glass-fibre-reinforced plastic, concrete, and wood are also used. The most common method of propulsion is by a diesel engine through a screw propeller. Since the early 19th century, but particularly in the late 20th century, ships have grown in size. A ship's size is measured in several ways. Merchant ships are usually referred to in terms of gross or net tonnage, a measurement of their capacity rather than their weight. Displacement tonnage, measured by the amount of water the ship displaces, is the chief size-measurement method for warships