Category How does It works, How things work, How is it done, Curiosity

A camera is a fairly simple piece of equipment in its basic structure. One must not be put off by the numerous levers, buttons, scales and other gadgets on the outsides. These are all extremely useful aids but are not completely essential.

The essential part of the machine is what gives its name: the camera obscura. This is Latin for dark room. Photographs are produced when rays of lights penetrate into this dark chamber. The light must enter through a small opening and strike against a sensitive film. The surface of the film is covered in an emulsion of chemicals which capture the images being carried by light rays. The small opening, or aperture, must also be able to open the aperture to let the light in. this mechanism is called the shutter. In a simple camera this is about the only moving part.

In more expensive cameras the fitting includes mechanism which can vary the exposure time which determines how long the shutter will stay open. The can range from a thousandth of a second for fast-moving subjects to one second or more for still dimly-lit scenes. Other controls include an aperture selector to vary the amount of light passing through the lens, and a focusing mechanism to produce a sharp image.

The camera obscura has long been known to man and Leonardo da Vinci made accurate drawings of it in the fifteenth century. It was not until 1839, however, that the first commercially available cameras were made in Paris by Alphonse Giroux for Daguerre.

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When the first railway began to operate it was suggested that a messenger should ride on a horse ahead of the train to tell people of its approach and warn the engine driver of any obstacles along the track.

Soon the train was able to travel much faster than the horse. Men with flags stood beside the track and either signaled the train-driver to stop or waved him on.

The problem of travel safety grew as trains increased in speed and numbers and level crossing with gates were built as well as viaducts to take trains over dangerous or difficult places.

Eventually a comprehensive system of mechanical signaling was evolved. Semaphore signals that swung up or down on a tall pole beside the track were the most common. Nowadays the majority of large railway stations have colour-lights signals, with red meaning ‘stop’ , green ‘go’ and amber ‘caution’.

All these signals are now worked electrically. It is no longer necessary for a man with a watch to check the various times when trains pass, open gates or decides which track the train will go on to and make a note of trains which have been delayed. Today all these tasks are done by computers and the signal posts of large stations are completely automated.

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Sometimes films are shots or photographed without sound: the dialogue is added later together with sound effects and other noises. When these sounds are added the noise of a waterfall might be produced by merely shaking water about in a basin or the voice of a stage actor might replace that of the film actor in a process known as dubbing.

The major developments in cinematography were the introduction of sound in 1927 and the advent of colour photography.

The cinema really grew up as an art after the Second World War but it found an extremely dangerous rival in television. So the film industry began to think up counter attraction. These included the evolution of wide screens as in the processes known as Cinema Scope and Cinerama. In wide-screen presentations, a special lens may be used that spread out the image on the film to fill the screen. When the film is shot, a similar kind of lens is used to squeeze a wide field of view on to standard film. Modern cinemas in addition may also use stereophonic sound which is emitted by numerous loudspeakers. This gives the audience the impression that they are might in the middle of what is happening.

The story of the cinema is not yet finished. Scientists are studying a way of producing satisfactory three-dimensional films so that the images are no longer flat. Experimental have also been carried out with a circular screen that completely surrounds the audience.

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The first step towards making a film is the idea for the subject. The next requirement is money to pay for all the production costs. The producer is the man who raises this money and generally he chooses the director, the most important man in making a film. The director then appoints a writer to prepare a screenplay which is like a stage play but consists of hundreds of short scenes which finally make up the whole film.

A film studio seen for the first time is quite an overwhelming sight. You may see a straight road lined with marble columns representing a roman road of 2000 years ago. Near this scene there might be a ramshackle prairie town of the Wild West. In another part of the studio there may be a magnificent governor’s palace set in imperial India. The studio is therefore crowded with Roman soldiers or gladiators, cowboys or young English colonial ladies. Some part of the studio will probably be very strictly cordoned off because a film crew may be ‘shooting’ there.

Today film directors prefer to work on location which means they film their scenes in real places outsides instead of creating them from plaster and wood inside a studio. Other film crews with their actors and actresses travel from one continent to another. But when a film is historical or period piece it is usually shot inside a studio. Films employ armies of technicians. Skilful carpenters and scene painters build intricate structures known as sets which can be of medieval castles, or of ultramodern apartments.

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Modern science and technology have made it possible, among other wonderful things, to make a permanent record of sounds and human speech. The tape in a tape recorder is made of an insulation material on which a thin magnetic layer has been placed. The tape is normally 3 millimeters wide in cassettes and 6 millimeters in reels. How does a tape recorder work?

There is a motor which turns a reel of tape from the supply wheel to the take-up reel. The tape passes across the recording head. When we speak into the microphone the voice is turned into a series of electrical impulses. These impulses are caught on the tape in various patterns. In video tape recordings the light signals are turned into electrical impulses recorded on the tape.

When the tape is played back it runs past an electromagnet. The magnetic patterns that have been recorded along the magnetized tape set up a variable magnetic field with the electromagnet.

The impulses of this magnetic field are the converted into sounds which are amplified and played through a loudspeaker to re-emerge as the original speech or music that was first fed into the tape recorder.

Today tape recorders are very popular. Besides being easy to operate they have the added advantage that recordings can be erased and the tape used many times. A new compact type of tape recorder is the cassette recorder. The works on the same principle but use narrower tape in its own self-contained cassette.

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 Even air has weight and, like any solid object, it presses down on the surface of the Earth. Scientists decided to measure the amount of his pressure and the Italian Galileo was the first to succeed. He used a very long tube, closed at one end, which he filled with water and then placed the open end in a receptacle full of water. The water in the tube fell, stopping at a height of 10 meters. A few years later, in 1643, a pupil of Galileo named Evangelista Torricelli carried out further experiments using a heavier liquid than water; mercury. The mercury rose inside its tube, closed at one end, which he filled with water and then placed the open end in a receptacle full of water. The water in the tube fell, stopping at a height of 10 metres. A few years later, in 1643, a pupil of Galileo named Evangelista Torricelli carried out further experiments using a heavier liquid than water: mercury. The apparatus was given the name barometer from, the Greek baros meaning ‘weight’ and metron meaning ‘measure’. Torricelli soon noticed that the height of the mercury column varied with changes in air pressure. About 1647 Blaise Pascal’s experiments finally convinced people of the correctness of Torricelli’s ideas.

The most modern form of this instrument is the aneroid barometer, from Greek a meaning ‘without’ and neros meaning ‘liquid’. The aneroid barometer consists of a small steel box which contains a vacuum. The pressure of the air outside the box can cause the surface of the box to move in or out. A needle on the dial records the movements of the box along a graduated scale to show the changes in air pressure.

This type of barometer is smaller and more portable than a mercury barometer but it is not quite as accurate. It has first to be calibrated or set to a mercury barometer before it can be used.

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