Scientific Appliances And Their Working Principles

• Scientific Appliances And Their Working Principles
  Aeroplane: An aeroplane usually consists of the following three parts: (i) Wings, (ii) The engine and the propeller; and (iii) The tail. Working: In order to operate an aeroplane, the propeller is made to revolve at a very high speed with the help of a powerful petrol engine. The direction of the blades is so adjusted as to push the air in a backward direction, thereby producing a relative velocity between the ’plane and air—thus pushing the aeroplane in a forward direction. The push should be large enough to overcome the drag  and should supply power for climbing.
  
  Air conditioning: is the process of controlling the humidity, temperature, purity and circulation of air in a certain factory, a public building, hotels or a private house. The major aim of air-conditioning is to regulate the temperature, thereby producing a “cooling effect” on the whole. Exhaust machines are devised at a particular place for driving out waste and dirty gases, thereby completely purifying the air.
  
  Binoculars: is an instrument used for seeing distant objects; the rays of light are twice reflected by means of right-angled prisms.
  
  Carburettor: It is an apparatus for getting liquid fuel mixed with air as it is taken into an automobile or other like engines.
  
  CD-Rom: It is a computer peripheral device that employs compact disk technology to store large amounts of digitized data for later retrieval.
  
  Cellular Phone: This phone allows you to make a telephone while on the move. It can be installed in vehicles or can be carried along.
  
  Cinematography: The  principle  of  persistence  of vision is utilised in cinematography. A cinematograph is an apparatus for projecting the pictures of moving objects on the screen. The instantaneous photographs of the successive positions of the moving body are photographed on a continuous film with the help of a special camera called the movie camera, with an automatic shutter at the rate of nearly 16 per second. The film duly developed is projected intermittently with a similar shutter as above so that it opens when the film is stationary and closes when it jerks off.
  
  Computer: A complicated electronic machine which can perform incredibly complex calculations at incomprehensible speeds. It was invented by Charles Babbage. It can do whatever we know how to order it to perform. A computer consists of a Central Processing Unit (C.P.U.) and a number of peripheral units. A computer does not do anything which a human being cannot do. Only that it does is much faster and accurately.
  
  Dewar Flask: is a double-walled glass flask, the inner surface of the outer vessel and the outer surface of the inner vessel of which have been silvered. The vacuum is created in the space between the two walls. This principle successfully prevents any interchange of temperature of the contents, because: (1) glass is a bad conductor (2) convection is not possible because there is vacuum between the walls and (3) a little radiation that takes place from the inner vessel is reflected by the inner surface of the outer wall.
  
  Daniel Cell: In this a rod of zinc is placed in dilute sulphuric acid contained in a cylindrical porous pot. The porous pot and its contents are placed in a large cylindrical copper vessel which also functions as positive pole of the cell. The space between the porous pot and the copper vessel is occupied by a solution of copper sulphate. The hydrogen produced by the action of the zinc on sulphuric acid travels towards the copper electrode. On delivering its electricity to the copper, it reacts with the copper sulphate turning copper out of the solution and forming sulphuric acid. The particles of copper liberated from the solution adhere to the outer copper vessel and thus the hydrogen is rendered harmless so far as polarisation is concerned.
  
  Diesel Engine: It is a particular type of internal combustion engine, known as compression ignition engine. The air inside the cylinder is usually compressed to over 500 lbs. per sq. in. and the temperature is attained up to 800°F. At this stage the oil is injected into the hot compressed air, which gets ignited immediately, thereby producing a continuous gas stream, which pushes the piston upward. And thereafter the engine gets into operation.
  
  Dynamo: The origin of the electricity in a dynamo is the transformation of mechanical energy into electrical energy. It depends on the principle of electro-magnetic induction whereby a current is produced on traversing a magnetic field.
  
  Electric Bell: In an electric bell, there is one horse-shoe electromagnet, which plays an important role. A soft iron armature which is connected to a hammer H, is placed in front of the pole pieces of the electromagnet.
  One end of the coil of the electromagnet is connected to the terminal T2  while the other end is connected indirectly to the terminal T1 (i.e., through the soft iron armature which rests on the spring contact as shown in the diagram).
  On connecting the terminals T1 and T2  through battery, the electromagnet attracts the soft iron piece, and the hammer H in turn strikes the gong G, which produces a sound. Simultaneously, the contact between the spring and the screw breaks which demagnetises the electromagnet and the soft iron piece falls back to make up the circuit once again. The process is repeated again and again, which produces a continuous sound.
  
  Electric Lamp: The electric lamp is based on the principle that when an electric current is passed through a very fine metallic filament inside an evacuated glass bulb, it is heated so as to render the wire white hot or incandescent. The wire being very thin offers great resistance to the passage of the current so that considerable heat is developed and the temperature rises to make it luminous and thus emit light. The resistance generally increases as the temperature rises and soon an equilibrium is reached and there is no further rise of temperature, the amount of heat radiated by the filament being equal to that generated in it by the electric current. In order that the metallic filament shall not oxidise or rust, oxygen is removed from the bulb by pumping out air or generally some inert gas such as nitrogen or some other gas is made to fill the bulb.
  
  Electric Motor: An electric motor is a device which converts electrical energy into mechanical energy. A D.C. motor generally consists of several segments of a coil of a wire of a large number of turns wound over a soft iron cylinder called the armature. It is mounted on an axle about which it revolves and is placed between the poles of an electromagnet called the field magnets.  There are the commutator, brushes and the leads. It is based on the principle that a conductor carrying current experiences a force when placed in a magnetic field.
  
  Electro Cardio-gram (E.C.G.): It is actually a graphic picture of the heart-beat which the physician can make use of in the diagnosis. When the heart beats, its muscles contract and this causes a change in the electrical potential of the system. This change in potential is recorded on a paper by an electrical instrument known as electrocardiograph. The electrodes are connected to the two wrists and the left leg of the patient, and the machine acts like a galvanometer, the needle of which rests on a rotating drum covered with a paper, and thus the movements of the needle are recorded.
  
  Electromagnet: whenever an electric current passed through a coil of wire, a large number of turns, wound round a soft iron core, the iron core gets magnetised and it becomes a powerful magnet, and is known as an electromagnet. This magnetism is temporary and lasts so long as the current passes through the coil. Looking at the end of the soft iron bar if the current in the coil is clockwise in direction that end of the bar is South Pole; if the current is counter-clockwise, that end is a North Pole.
  
  Electron Microscope: It is just analogous to optical microscope in a way that beams of electrons are focused by magnetic lenses in a similar way to the focusing of light beams in the ordinary optical microscope. Germans were the pioneer to invent the electron microscope, during the year 1930. Direct  magnification up to 10,000 times is possible. Still higher magnification is possible with the Proton Microscope.
  
  FAX: Short for facsimile, it is a device that transmits pictures, drawings, text to a similar device at the receiving end, using telephone lines.
  
  Fibre Optics: It is a branch of physics based on the transmission of light through transparent fibres of glass or plastic. These optical fibres can carry light over distances ranging from a few inches or centimetres to more more than 100 miles (160 kilometres). Such fibres work individually or in bundles. Some individual fibres measure less than 0.004 millimetre in diameter.
  Optical fibres have a highly transparent core of glass or plastic surrounded by a covering called a cladding. Light impulses from a laser, a light bulb, or some other source enter one end of the optical fibre. As light travels through the core, it is typically kept inside it by the cladding. The cladding is designed to bend or reflect-inward-light rays that strike its inside surface. At the other end of the fibre, a detector, such as a photosensitive device or the human eye, receives the light.
  Uses of Optical Fibres: Optical fibres have a number of uses. Various industries use optical fibres to measure temperature, pressure, acceleration, and voltage. In fibre-optic communication systems, lasers transmit coded messages by flashing on and off at high speeds. The messages travel through optical fibres to interpreting devices that decode the messages, converting them back into the form of the original signal. Fibre-optic communication systems have a number of features that make them superior to systems that use traditional copper cables. For example, they have a much larger information-carrying capacity and are not subject to electrical interference. In addition, signals sent over long-distance fibre-optic cables need less amplification than do signals sent over copper cables of equal length.
  Optical fibres are well-suited for medical use. They can be made in extremely thin, flexible strands for insertion into the blood vessels, lungs, and other hollow parts of the body. Optical fibres are used in a number of techniques that enable physicians to look and work inside the body through tiny incisions.
  
  Fire Extinguisher: works by spraying continuous streams of carbon dioxide gas, which does not support combustion, and so acts as a fire extinguishing agent. Fire extinguisher is a medium size metallic cylinder fitted with a head-knob and a handle. At the time of emergency, the knob is struck against the floor, and carbon dioxide gas begins to evolve. Inside this cylinder a bottle of dilute solution of sulphuric acid is embedded in sodium carbonate powder. When the bottle is broken, sulphuric acid reacts with sodium carbonate to produce large quantities of the gas.
  
  Fusion Torch: is an instrument to be evolved by the U.S. Atomic Energy Commission. It will use the power of the Hydrogen bomb to vaporise solid waste like junk-cars and bearcans, into their basic elements. The idea is based on the assumption that within a few years scientists will be able to harness the energy of the Hydrogen bomb—Controlled thermo-nuclear fusion—for use in electrical power plants.
  
  Geiger Counter: A G.M. counter or Geiger-Muller counter is a device used for detecting and/or counting nuclear radiation and particles.
  
  Heart Lung Machine: A machine which operates the function of the heart and lung at the time when the heart or lung is under operation. It directs the circulation of blood into body.
  
  Incandescent lamp: If a body of sufficiently high melting point say platinum wire is raised to a high temperature, some of the radiations coming out fall within the range termed “light”. The range comprises of radiation of short wave lengths and high frequencies. When such a body is heated it emits different colours at different temperatures, and ultimately, it gives dazzling white light at 1500°C and above. So the incandescent lamp consists of a metal of a high melting point (generally tungsten) enclosed in an evacuated glass globe and heated by an electric current. The filament is either in the form of an open spiral of straight wire or in the form of a ring of coiled wire. This lamp consumes about 1.4 watt per candle.
  
  Internal Combustion Engine: is an engine in which energy supplied by a burning fuel is directly transformed into mechanical energy by the controlled combustion of the fuel in an enclosed cylinder behind a piston. It is usually applied to the petrol- burning or Diesel oil-burning engine.
  
  Jet Engine: The essential components of the jet engine is the Gas turbine. It drives the rotary air compressor, which supplies compressed air to the combustion chamber, where a fuel like kerosene oil or gasoline enters and burns. The hot exploded gases are then expelled to the rear in a high velocity jet exhaust. It is the reaction of the plane on this jet of ejected gases that drives it forward.
  
  Jet Propulsion: It is now being commonly employed for propulsion of aircraft and the underlying principle is Newton’s third law of motion, that is, “to every action there is an equal and opposite reaction”. Here a gas turbine drives the rotary air compressor which supplies compressed air to the combustion chamber, where the fuel-like gasoline enters and burns. The hot exploded gases are expelled to the rear in a high velocity jet exhaust. It is the reaction of the ‘plane on this jet of fastly ejected gases that drives it forward. It has made possible supersonic speeds.
  
  Difference between Rocket and Jet Engine: The essential difference between the propulsion of a jet engine and a rocket is that the gas turbines used in a jet engine require air to supply oxygen for the burning of the fuel. Rockets contain both fuel and an oxidizer to make them burn. Liquid oxygen is often used. So a jet engine would work only in the lower strata of the atmosphere where sufficient oxygen can be supplied by the air-compressors. The high velocity jet from a rocket is available for thrust in the upper atmosphere and even beyond the limits of our atmosphere. For rocket flights of course, the wings and rudders would be absolutely useless since there would be no air to exert force on them.
  
  LASER: or Light Amplification by Stimulated Emission of Radiation, LASER is a device that harnesses light to produce an intense beam of radiation of a very pure, single colour. The power of the beam can be low (as in a food store laser scanner which reads prices on packages) or high (as in lasers used to cut metals). The first laser was built in 1960.
  
  Lightning Conductor: It consists of a metal rod, the upper part of which is made up of copper with a number of conical points, the lower portion being an iron strip which extends deep into the earth’s moist layers. A lightning conductor protects the building from the effect of lightning in two ways: (i) The pointed conductors are charged by induction oppositely thus setting up an opposite wind which brings about a slow and silent discharge of the cloud. (ii) If however the lightning does strike, the discharge may be carried to the earth through the metal strip without doing any damage to the building. In ships also, lightning conductors are fixed to the masts and carried down through the ship’s keel-sheathing.
  
  Loud Speaker: It is a device for converting electrical energy into sound energy. There are various types of loud speakers but the commonest and most efficient type used now-a-days is the moving coil type. It is based on the principle that when a varying current is passed through a conductor in a magnetic field, the conductor is acted on by a variable force and if the current is oscillatory, the conductor is set into vibrations.
  
  Mariner’s Compass: is an apparatus which is used to guide the sailors. The needle always points north-south. It consists of a magnetised bar with a card bearing the directions viz., north, south, east etc. The card is correctly mounted above and firmly attached to the magnetised bar. When the magnet moves in relation to the ship’s course, the card automatically moves with it.
  
  Motor-Car: A motor-car usually consists of the following working parts: (i) Internal combustion engine (ii) Gear Box (iii) Battery (iv) Carburettor (v) Dynamo (vi) Radiator.
  Working: In order to operate a motor-car, the petrol from a container is ignited with the help of the battery. The vapours produced thereof are allowed to mix with air in the carburettor section, and thereafter the mixture is allowed to enter the cylinder of the internal combustion engine. The gases on expansion push the piston upwards thereby moving the crank-shaft, which in turn moves the main axle of the car. The motion of axle is controlled by the gear box.
  
  Periscope: It is a device for viewing objects which are above the eye-level of the observer, or are placed so that direct vision is obstructed. It is usually used by the crew of a submarine to survey the ships etc., on the surface of the sea while the submarine is under water. It also enables sailors to observe objects on the other side of an obstacle without exposing themselves. It consists of a long tube, at each end of which is a right-angled prism, so situated that, by total internal reflection at the longest faces, light is turned through an angle of 90° by each prism. The light from a viewed object thus enters the observer’s eye in a direction parallel to, but below, the original direction of the object.
  
  Phytotron: is a big machine costing two million dollars and capable of producing any type of climate to order. It has been installed in Duke University, Durham, North Carolina to facilitate studies of environmental biology—particularly growing of plants under varying climatic conditions. The machine can duplicate any set of climatic conditions from the tropical to the Arctic in the brick and glass building in which it is housed. It has six specially equipped green houses and 40 controlled plant chambers. It is a useful device for the study of environmental biology.
  
  Radar: precisely means: Radio, Angle, Detection And Range. It is one of the interesting developments of wireless waves the principle of which has been utilised in the radio location technique or popularly known as RADAR. It is an electrical device used for the detection and location of the aircraft with the help of radio frequency waves.
  Working: Wireless waves having very short wavelengths are set free in the shape of concentrated beam to flood or cover the required area of the sky. An aircraft entering that particular area is supposed to intercept the spreading waves, and an echo is reflected back to the transmitting station. In addition to detection of the aircraft, its distance from a particular place can also be calculated by recording the time taken by the wireless waves in travelling back. A discrimination between the aircraft of an enemy and a friendly nation can be made by understanding the nature of Echo.
  
  Refrigerator: It is an apparatus or chamber for producing and maintaining a low temperature. The principle employed in the working of a refrigerator is that heat is absorbed by a liquid as it evaporates, thus producing a cooling effect. The substance commonly employed is liquid ammonia sulphur dioxide.
  
  Rocket: The underlying principle of the flight of a rocket is Newton’s Third Law of Motion viz., To every action there is an equal and opposite reaction. It is a self-propelled vehicle which depends upon the force provided by a fuel carried along with it. As the fuel burns, products of combustion are forced out at terrific speed at the rear of the vehicle and ejection imparts motion to it in the forward direction. It has its own oxygen supply for burning the fuel and therefore, there is no dependence on air for combustion or propulsion.
  
  Rocket Bomb: If a rocket engine is used as a missile to carry an explosive charge it is termed as a Rocket Bomb. The principle of a rocket engine is the same as that of a jet engine but unlike the jet engine it carries its supply of oxygen with it to burn the fuel and is thus independent of the oxygen of the air. The hot gases formed in the combustion of the fuel are led through a nozzle. If a quantity of gas of mass m leaves the nozzle in time t with a velocity v, the force exerted on the mass of gas and hence the force also on the rocket = mv/t. Such a rocket bomb can be hurled from a place outside our atmosphere.
  
  Safety Lamp, Davy’s: It is based on the principle of rapid conduction of heat by a metal. In the miner’s safety lamp, the flame of the lamp is surrounded by glass and above this is a space surrounded by five copper gauzes. Inflammable gases which may be present in the mine can pass through and burn inside the lamp. The copper gauze conducts away the heat so rapidly and effectively that the ignition point of the gas outside the gauze is never reached and thus the possibility of an explosion is avoided.
  
  Seismograph: It is an instrument used for the registration of earth tremors, and consists of principle of a heavy pendulum system, the supporting framework following the ground movements and the bob remaining at rest on account of its large inertia thereby setting up a relative movement between the two parts of the seismograph. This movement is recorded with the help of electromagnetic transducers, galvanometers and electronic amplifiers. In order to record the displacements completely, usually three seismographs are made to set at one particular station.
  
  Sound Barrier: Before the advent of aircraft with supersonic speeds, it was apprehended that when the speeds of the aircraft and sound were equal, the compressional waves produced by the flight of the aircraft will be unable to get away and will give rise to a sound barrier which will offer a considerable resistance to the motion of the aircraft and huge structural stresses and strains will be called into play attended by great noise likely to react unfavourably on the crew. But no such effects have been observed now that the speed of the jet-propelled aircraft and rockets far exceeds that of sound.
  
  Spring Balance: A Spring Balance is used for measuring weights. The principle involved is that the stretching in the case of a Spring is proportional to the load suspended and if a load of 1 kilogram produces a stretching of 1 cm, a load of two kilograms will stretch it by 2 cm and so on. The spring is held at the upper end and load is suspended by a hook attached to the lower end with a pointer attached to the upper end of the spring which moves over a scale.
  
  Steam Engine: is a machine utilizing steam power through a device by virtue of which heat is converted into mechanical energy. The steam engine has two main parts: (i) boiler, and (ii) proper engine. It consists essentially of a cylinder in which a piston is moved backwards and forwards by the expansion of steam under pressure.
  
  Stereoscope: It is an optical device that makes photographs seem to have three dimensions. An ordinary camera sees things only in a flat plane and never in the round. But if two cameras set several inches apart photograph the same object simultaneously, and if these two photographs are then mounted side by side and viewed through a combination of lenses and prisms in such a manner that the two units enter the two eyes without strain, the resulting mental picture (image) appear to have three dimensions. Everything is seen in the round, the way our two eyes normally view things. These are employed in aerial survey and in astronomical telescopes.
  
  Submarine: may be regarded as a ship having a variable and controllable specific gravity. It is equipped with large ballast tanks (in the low, the middle and the stern of the ship) into which water can be admitted through valves so that the vessel can be made to sink when desired. On the water being expelled again by pumps worked by compressed air, the ship rises to the surface. Inside the water it is the electric motors which drive it forward and there are horizontal rudders (or hydroplanes) which are fitted on both sides of the vessel so that by tilting them the vessel is gradually submerged, the same rudders help to maintain it at a desired depth of submergence.
  
  Tape Recorder: It is an instrument which converts sound waves into electrical impulses which are recorded as a wavy groove on the tape.  When it is required to produce the voice, the electrical impulses are again converted into sound waves.
  
  Telephone: It is a device to produce sound to enable two persons to talk to each other from distance. The circuit, which is closed when the line is connected, consists of a transmitter and a receiver connected by an electrical conductor. The transmitter which is usually a carbon microphone causes variable electrical impulses to flow through the circuit. In the telephone-receiver, these impulses flow through a pair of coils of wire wound upon soft iron pole-pieces which are attached to the poles of a magnet. An iron diaphragm near these coils experiences variable pulls and vibrates so as to produce sounds corresponding to those made into the microphone.
  
  Telephotography: is a process by which the transmission of moving objects is made by radio from one place to another. A succession of still pictures is transmitted at the rate of twenty-five per second which gives an illusion of continuous movement. The television camera changes the light pattern of the transmitted scene into a series of electrical signals which modulate a very high frequency radio carrier wave. The received signals are changed into light variations and reassembled on the screen of a cathode-ray tube at the receiver.
  
  Teleprinter: It is an instrument which prints automatically messages sent from one place to another. It consists of a telegraph transmitter with a type-writter key-board by which characters of a message are transmitted electrically in combination of 5 units, being recorded similarly by the receiving instrument. The receiving instrument then translates the matter mechanically into printed characters.
  
  Telescope: A simple refracting astronomical telescope is an optical arrangement for seeing very distant objects. Two convex lenses are mounted at the ends of two tubes so that by sliding one tube within the other, the distance between the lenses can be changed and the images thereby can be focused correctly. The lens at the larger end of the telescope is of considerable focal length and is called the object glass and a smaller lens of short focal length is called the eye-piece. Parallel rays proceeding from a distant object form its real image at the principal focus of the object glass. The position of the eye-piece is adjusted so that a magnified virtual image of it is seen. Since the real image is inverted, this virtual image is also upside down—a fact of little importance in astronomical work. For viewing terrestrial objects, the real image formed by the object glass is re-inverted by another convex lens before it is magnified by the eye-piece.
  
  Television: It is the transmission of images of moving objects by radio waves. The scene to be transmitted or its image on a photo-mosaic inside an iconoscope camera is scanned with the help of a fine beam of light traversing horizontally and vertically. The reflected pulses in the former case are picked up by photoelectric cells which convert light energy into varying electric currents, or in the latter case, the photo-mosaic with the help of suitable electrical circuits generates varying currents. These currents are amplified with the help of valve amplifiers and are then made to modulate the carrier waves from a transmitter. At the receiving station, the electrical vibrations are reconverted into light waves which are collected on the fluorescent screen of a cathode ray oscilloscope at the same rate with which they are generated at the sending station. With the help of the property of persistence of vision possessed by the eye, we can see on the screen an exact photograph of the transmitted scene.
  
  Thermometer, Clinical: A clinical thermometer is used to note the temperature of a human body and has graduations from 65°F to 100°F. It consists of a thin glass bulb connected with a thick walled capillary tube known as the stem. There is a constriction in the bore near the bulb. When the thermometer is placed below the tongue (or in the arm-pit) of a person, mercury in the bulb gets heated and expands. The force of expansion pushes the mercury past the constriction, which thus rises into the stem. When thermometer is removed, the temperature falls and mercury contracts. But the level remains intact as the thread is now broken at the constriction. The temperature can thus be conveniently read. The mercury can be again brought into the bulb by giving it a slight jerk.
  
  Thermos Flask (Vacuum Flask): It is used to keep hot liquids hot and cold liquids cold. The principles involved in its construction are: (i) It is made of glass which is a bad conductor of heat; (ii) As there is vacuum between the walls, convection is not possible; (iii) The outer face of the inner vessel is silvered, so there is very little radiation as polished surfaces are bad radiators. The inner surface of the outer vessel is polished which serves as a good reflector of any small radiation from the inner surface.
  
  Tokamak T-3: is a machine designed by Russians to harness fusion reaction for peaceful purposes. A fusion reaction takes place under extreme pressure and temperatures such as exist in the core of the sun. In this machine such conditions are created by generating a hot gas or plasma. The Russians are already at work on an improved version of the machine which should achieve self-supporting generation of fusion-energy.
  
  Transformer: It is an apparatus by which the voltage of an alternating current is made higher (step-up Transformer) or lower (step-down Transformer) or its frequency. Transformer is made up of two coils, one of a small number of turns of thick wire and the other of a great number of turns of thin wire. A current going through the first of these causes an induction current of higher voltage in the second. If the main current goes through the second one, induction current of a lower voltage is generated in the first coil.
  
  Transistor: It is an active component of an electric circuit which may be used as an amplifier or detector. It consists of a small block of a semi-conducting material to which at least three electrical contacts are made, two of them being closely spaced rectifying contacts generally and one ohmic or loose (non-rectifying) contact. Transistors are now being used in radio receivers, in electronic computers, in electronic control equipments, in place of vacuum tubes where the required voltages are not too high. They are much smaller than their vacuum tube counterparts, consume less  power and have no filaments to burn out.
  
  Ultrasonoscope: It is a compact, diagnostic instrument designed to measure and use ultrasonic sound (with a frequency higher than 20,000 cycles per second, beyond human hearing). It emits brief bursts of ultrasound which are reflected back by bone, fluid or tissue in the body and give an “echo-gram”. The instrument can be helpful in detecting deep-seated brain tumours, defective heart valves and abnormal growths.
  
  Videophone: The world’s first commercial videophone service was started for limited experimental use in Pittsburgh, Pennsylvania. It is as much of an advance on the ordinary telephone as the addition of sound and colour was to the movies. The visual dimension also increases the functional utility of this communication apparatus, but the trouble so far has been in designing and making videophones which will be cheap enough to be installed and used by thousands of people.