Did the ancients have mechanical watches?

Antikythera is a Greek island about 40 km from Crete. In 1900, divers discovered the remains of an old ship near Antikythera.

In the ship there were marble and ceramic objects from the first century BC. They also discovered a bronze object in the shipwreck that had been eaten away by time. This object was finally forgotten for years in a museum storeroom.

In 1955, a scientist decided to clean the old bronze object. When the scab was removed, the object turned out to be an instrument of some kind. It had a series of gears that fitted perfectly into each other. The device is thought to be an astronomical clock, but the way it worked is unknown.

Such objects were never mentioned in ancient Greek or Roman writings. If it were not for the work of a curious scientist, perhaps it would never have been known that such an enigmatic "clock" existed.

How does a thermometer work?

   The thermometer on your wall is a glass tube with a silvery or red or blue line inside. The silvery line is a liquid called mercury. Since the tube is hollow, the mercury can move. It goes up as the room gets warm and down when the room turns cold. A thermometer with a colored line contains a different liquid that behaves in the same way.
    The marks and numbers on the tube measure the height of the mer­cury. If it shrinks down to the 32-mark, you will be shivering, and water will turn to ice. But when the mercury goes up as high as 90, you feel very hot.
Why does the line of mercury grow taller or shorter? Like everything else, mercury is made of tiny particles called molecules. The mer­cury molecules are always moving, bumping into each other and bouncing away. Even when the silvery line remains steady inside the tube, the molecules are shifting around and around. Heat makes them move faster. The fast-bouncing molecules shove each other farther and farther apart. So the mercury takes up more space, and it rises in the tube.
   When the molecules get cold they move more slowly. Now they don't need so much bouncing space. They draw closer together, and the mercury goes down.

How does a periscope work?

A periscope is constructed and functions similarly to a telescope, with a long tube containing a mirror at each end. The mirrors are mounted on the tube so that they are parallel to each other at a 45° angle to the axis or imaginary centerline of the tube.

In more advanced periscopes, additional lenses have been added to enlarge the image. Underwater periscopes are even more complicated. They have reflective prisms on the top and bottom of the tube, with two telescopes and several lenses between the two ends, and an eyepiece on the observer's side. The underwater periscope also has a thick, rigid waterproof cover and can withstand water pressure at great depths.

In addition to submarines, war tanks also use periscopes to search for enemy targets. Both vehicles have a periscope that can be raised or lowered, as well as turned in a 360° circle.

Periscopes can also be built so that they see around corners!

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How can an x-ray see inside the human body?

X-rays are like ordinary rays of light, except for one thing, they have a shorter wavelength. Because of this, a beam of this length has more energy and will be more penetrating than a simple beam of light, even through solid substances such as wood, metal and concrete.

An X-ray machine has a high voltage current flowing through X-ray tubes. Inside each tube is an airtight glass container. Inside it are two electrodes, or terminals, one negative and one positive. The negative is called a cathode. It is a tungsten coil that is heated by an electric current causing it to release electrons, or charged particles.

These electrons travel from the cathode to the anode, or positive, at very high speeds, from 96,000 to 282,000 kilometers per second. The anode, also called the target, is usually a tungsten block.

The anode stops the fast electrons. Some of the energy of the electrons is transformed into heat and the rest into X radiation. This X radiation, or X-rays, escapes through a window of the tube and goes to the part of the body that is going to be x-rayed.

Since these X-rays pass through the body, they cast shadows on a piece of photographic film, much like the film used in an ordinary camera.

In the hands of qualified technicians, X-rays can help save lives by killing cancer cells, helping doctors spot broken bones and diseased organs in a person's body, and even sterilizing medical supplies that cannot be boiled.

X-rays are also used in commerce and industry to locate product defects and to examine luggage at airports. But X-rays can also cause harm to humans by destroying healthy tissue, causing cancer and skin burns, and even modifying genes that pass traits from one generation to the next.

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How does the air conditioning work?

An air conditioning machine controls more than the temperature of the interiors. It also controls the amount of moisture, movement, and purity of the air. We have come to rely on air conditioning systems to keep us comfortable during the summer months.

The machine used to generate air conditioning works similarly to a kitchen refrigerator. Both rely on a fast-evaporation liquid to quickly cool what comes in contact with it.

When an air conditioner switch is turned on, fresh air passes through a filter to remove dust, and an electric motor begins to circulate refrigerant from a compressor through tubes or coils. While the refrigerant is being pumped through the coils, it absorbs the heat from the coils, cooling them together with the air around them.

The added heat causes the refrigerant to evaporate into a gas. At this point, an electric fan blows cold, clean air through the air conditioning vents in the room. The refrigerant becomes a liquid again when it returns to the compressor. This cycle continues indefinitely until the system is shut down.

Since the 1940s, all new buildings, factories and many private properties have been designed to include air conditioning. Boats, airplanes, offices, restaurants, theaters and shops make use of this constant flow of pleasant, purified air.

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How does a soldier see in the dark?

The night sight can turn night into day for the soldier, which means that darkness no longer protects the adversary. The night sight allows to detect the movements of the enemy, exposing him to the precise shot.

Such an artifact looks like a telescopic sight: it makes it possible to see on any night that is not completely dark. A very sensitive photoelectric cell converts the image into an electrical signal, as it would in a television camera. Circuits like a high-fidelity amplifier amplify the signal. Then they turn it back into an image and project it onto a small television screen.

Even in the darkest night there is usually some light, if only from the stars. In such a situation, the soldier can aim precisely at a target 365 m away. For artillery, tanks, helicopters and airplanes, more powerful versions with a range of one kilometre are used.

If there is not even the slightest stellar light, a different instrument can be used, the infrared camera, which detects heat rather than light. Objects that generate heat - for example airplanes, missile nozzles or campfires - can be detected within a radius of several kilometres. These sights are routinely used in surveillance operations. Infrared cameras can also detect body heat.

When every soldier, tank and airplane is regularly equipped with night sights, combat will be possible 24 hours a day.

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What was the biggest bicycle in history?

During the 1890s, a group of artists traveled through Europe and America with a giant bicycle they proclaimed was the largest ever built.

This bicycle was about 7 m long and had ten seats. But 20 years earlier, a Danish bicycle manufacturer had already built what was the largest bicycle in history: 21.6 m long and 34 seats!

The largest three-wheeled vehicle, a tricycle, was built in 1897. It weighed 1,360 kilograms, was 5 m long, and supported eight men. The rear wheels were 3.30 m apart.

Compare these giants with the smallest bicycle ever built - a bicycle of a little less than a kg that could fit in the palm of the hand. The wheels of this bicycle were about 5 cm apart, and the small device could be driven by an adult man.

The unicycle, or vehicle with only one larger wheel built, was 9.60 m high!

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How does a Geiger counter work?

The Geiger counter is a device used to know how much radioactivity is present in a substance or in a finished area. The counter works in a similar way to a neon light.

In a neon light, an electric current excites the gas molecules inside the crystal tube, making them shine brightly. Like neon light, a Geiger counter consists of a gas tube, with two pieces of metal inside it. The radiation consists of particles traveling at high speeds and energy waves, and together, excite the gas molecules inside the counter tube as they pass through it.

The molecules of the excited gas establish an electric current between the two pieces of metal inside the tube. The metal is attached to an amplifier and a meter, which increase and read the current. The strength of the current indicates the level of radiation. Also, depending on the force of the electric current is the volume of sound that the counter makes when it finds radioactivity.

Since a Geiger counter reads only radioactivity, it cannot be used to find metals such as silver or gold, which are not radioactive. However, it can be used to find uranium.

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Where does the boomerang come from?

For the past ten thousand years, Aborigines in Australia have used a type of weapon called bumerangs to kill the animals and birds they feed on. These weapons are designed to fly in a straight line to the victim, deliver a lethal blow and fall to the ground. The boomerangs that return to the thrower are smaller and lighter, and aborigines do not use them for hunting but only for recreational purposes.

In 1981, the official boomerang launch mark was established in Albury, New South Wales, in the Australian specialty championship: Bob Burwell, a telecommunications engineer, got a boomerang to fly 111 meters before it made the turn back.

For a boomerang to return it is not essential that it has its characteristic arched shape, since there are those with the shape of T, V, X and Y that are also capable of returning with the launcher. For the boomerang to be effective it is enough to splice two pieces of wood in the correct angle with an elastic league.

The shape of boomerang depends on of the wood they're made of. Those who return to the hand of the throwers can measure up to 75 cm and weigh almost 250 grams, and the hunting ones are usually more big and heavy. Boomerangs are sometimes decorated with red, white and yellow pigments.


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How does a barometer work?

aneroid barometer

The air also has its weight, and like all other bodies exerts a pressure, by the effect of gravity, on the earth's surface. Many scientists came up with the idea of measuring this pressure, but the first to do so was Galileo Galilei, using a very long tube closed at one end. He filled it completely with water, and put the open end into a container full of water: the liquid in the tube descended, stopping at a height of ten meters. Some years later, Evangelista Torricelli, Galileo's pupil, wanted to repeat the experiment with a liquid much heavier than water, that is, with mercury. The mercury rose through the tube up to 76 centimetres. The new device was called a barometer (in Greek, baros means weight and metron means measurement). Torriceli soon realized that the column varied in height according to pressure variations. More modern is the aneroid barometer (a = no; neros = liquid), consisting of a steel box in which a vacuum has been made: the external pressure displaces one of its faces inwards or outwards, acting on a hand that indicates the displacements in a graduated sphere, thus indicating the variations in pressure and its intensity. This type of barometer, also known as a metallic barometer, is less cumbersome, although it is also less accurate than mercury. In addition, before being used, it has to be adjusted with a mercury barometer.

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The gyroscope toy

   A toy gyroscope spins like a top. In fact, this toy is often called a gyrotop. The chief parts of the gyrotop are a wheel which is weighted around the rim and a rod, or axle, that goes through the center of the wheel. In spinning a gyrotop, a string is first wrapped around the axle. Then the string is pulled suddenly as the end of the axle is rested on something solid. Once a gyrotop starts spinning it does not change its position until it runs down. Its axle keeps on pointing in the same direction. It can remain in amazing positions as it spins. The whirling of the heavy wheel keeps it from falling.
   Not all gyroscopes are toys. Some are used in boats as compasses. Some are used to keep boats and airplanes on a straight course. A gyroscope used in this way is called a gyropilot. One nickname for a gyropilot is "metal Mike." In fighting at sea during a war gyroscopes are used to guide torpedoes. On some ships enormous gyroscopes are used to help keep the ships on an even keel so that passengers will not be seasick.
   Only toy gyroscopes are set to spinning by the pulling of a string. As a rule other gyroscopes are set in motion and kept spinning with electricity.

Electron microscope

   The electron microscope is an instrument which permits scientists to see and photograph objects too small to be seen with an optical MICROSCOPE. The electron microscope uses beams of electrons in place of beams of light. Its magnifying power is about 200 times that of the very best optical microscope.
   The human eye is a very fine OPTICAL INSTRUMENT. However, the eye cannot distinguish objects smaller than about four one-thousandths of an inch.
   The power of an instrument to enlarge and form a distinct image of small details is its resolving power. The limit of resolution of an optical instrument is the smallest distance between two objects for which the instrument can form two distinct images of these objects.
   The magnifying power of an optical microscope is thus limited by the fact that objects cannot be distinguished unless they are somewhat larger than the waves of light reflected from them.
   In 1932 Ruska, a German, constructed an electron microscope. He allowed a beam of electrons to be reflected from an object. (Since electrons are charged they can be controlled by electric and magnetic fields.) The reflected electrons were directed through a magnetic field and then focused on a screen (as electrons are focused on a television screen to make a visible image) or on a photographic plate so that the image would be recorded.
   The superiority of the electron microscope over the optical microscope depends on the fact that fast-moving electrons have a wave length a thousand times smaller than the wave length of visible light.
   In most cases an electron microscope must be used with objects which are very thin. Thus, stray electrons will pass through them rather easily. Only recently has it been possible to investigate living matter with an electron microscope.
   The electron microscope can be used to investigate a wide variety of materials. Many applications have been made in chemistry, biology, metallurgy and other fields. Many new structures have been discovered in insects. Details which occur in chemical changes have been seen.

What is a compressor?

   A compressor is a device that compresses a gas or vapor. Compressors provide the supply of compressed air for jet engines, paint sprayers, and rock drills and other pneumatic equipment. They are also used in the cooling systems of refrigerating units and air conditioners. The chief kinds are reciprocating, rotary, centrifugal-flow, and axial-flow compressors.
   Reciprocating compressors consist of one or more cylinders, each with an intake valve, a discharge valve, and a piston that is attached to a crankshaft. The intake valve opens on the downstroke of the piston and allows gas to enter the cylinder. On the upstroke the intake valve closes, and the piston compresses the gas and then forces it out through the discharge valve, which opens during the upstroke.
   Rotary compressors trap a gas between rotating blades or vanes that compress the gas into a steadily decreasing volume as they sweep it along.
   Centrifugal-flow, or radial-flow, compressors consist of two alternating sets of rotating blades enclosed in a casing. The rotation of one set of blades, called the impellers, forces the gas away from the rotating shaft toward the casing and at the same time increases the speed of the gas. The second set of blades, called the diffusers, tends to make the flowing gas slow down. In accordance with Bernoulli's principle, the reduction in speed increases the pressure of the gas.
   Axial-flow compressors also consist of pairs of moving and stationary blades and operate much like radial-flow compressors. In axial-flow compressors, however, the gas flows parallel to the shaft on which the moving blades are fastened.

What is a dehumidifier?

   A dehumidifier is an apparatus far removing water vapor from the air. A room dehumidifier is a small, portable unit that can be placed in the center of a damp room to dry the air. Most dehumidifiers operate by passing the moist air through a cooling device similar to the cooling coil of a refrigerator.
   Cooling makes the water vapor condense out of the damp air. The condensed vapor collects in a pan, which must be emptied periodically.

What is a Volmeter?

   A voltmeter is an instrument used to measure the voltage or difference in electrical pressure between two points of an electrical circuit. The meter is placed across that part of the circuit where the voltage is to be measured.
   Because direct current (DC) circuits have a steady voltage and alternating current circuits (AC) have a varying, pulsating voltage, voltmeter construction must be designed to allow for these differences.
   Direct currents are usually measured by a moving-coil, permanent magnet voltmeter or by a fixed-coil, moving magnet meter. The moving-coil meters use the most common of electric meter designs, the D'Arsonval movement. The current from the external circuit flows through the moving coil of the meter and sets up a magnetic field around the coil. This field opposes the field due to the permanent magnet, and the coil is made to rotate. The coil rotates until the force of the opposing magnetic fields is just balanced by the mechanical force of the springs on which the coil is suspended. The larger the current, the greater the rotation of the coil. Since a pointer is attached to the movable coil, as the coil rotates the pointer indicates the voltage-value on a scale calibrated (marked off) in volts.
   Fixed-coil, moving magnet voltmeters are, in principle, similar to moving coil meters except that it is the permanent magnet that rotates with the pointer attached. A fixed coil surrounds the magnet.
Alternating voltages are measured with moving-vane meters, THERMOCOUPLE meters, copper oxide rectifier meter, or vacuum tube voltmeters.
   In the moving-vane meter, a moving vane of soft iron is pivoted within a circular coil. When current flows through the coil, the moving vane is attracted by the field of the coil. As the vane moves, the pointer attached to the vane moves across a scale.
   In a thermocouple meter, the current passes through a coil which heats the junction of two dissimilar metals, usually bismuth and antimony. The electromotive force generated by the junction is fed to a D'Arnsonval meter.
   In a vacuum tube voltmeter, a vacuum tube isolates the input circuit of the meter from the circuit being measured. The AC is sometimes rectified by the tube and the resultant DC is fed to a D'Arsonval meter. At other times, the AC is merely amplified and fed directly to an AC meter.

Optical instruments

   Optical instruments are devices in which light is passed through lenses or prisms. Among the common optical instruments are the microscope, binoculars, camera, spectroscope, periscope, and telescope.

   In the 1500's and 1600's, the first optical instruments were developed, following the discovery of the glass lens. The earliest telescopes and microscopes evolved because of the lens.
   One of the original optical instruments to undergo numerous improvements was the spectroscope. In 1666 Isaac Newton sent a beam of light through a prism. The beam broke into a band of colored light, similar to a rainbow.

   One kind of SPECTROSCOPE is basically a glass PRISM. All materials, when heated hot enough, radiate light. When this light from a particular substance is beamed through a prism, it divides into colored areas that are distinct for the elements in that substance. A trained spectroscopist can use this instrument to determine the chemical composition of laboratory "unknowns" and the elements in the stars and the sun.

What is a speedometer?

   Scientists and engineers have mastered the measurement of distance - from fractions of a millimetre to thousands of kilometres. And they can also measure time with the same degree of accuracy. A combination of the two gives us a further important measurement - speed. Speed is the distance travelled by an object in a certain time. Measurements of speed are given by devices named according to the vehicle in which they are found. A ship has a log, an aeroplane has an airspeed indicator. And the most common of all is the speedometer, which is found in motor cars and trains.

   An important part of a speedometer is the magnet. A magnet's force is spread out around it in the form of a magnetic field. When a magnet is rotated, its field will rotate with it. The magnet in the speedometer begins to rotate as soon as the vehicle starts to move.

   The magnet is driven by a flexible cable which is connected to the front axle of the vehicle. The higher the speed of the vehicle, the higher is the speed of rotation of the magnet. The magnet rotates inside an aluminium ring. The rotating magnetic field brings about ('induces') electric currents within - the aluminium metal. These in turn give rise to a second magnetic field. This magnetic field repels the one produced by the magnet itself.

   This force on the ring is called the torque. The faster the magnet turns the higher is the torque. The ring is not free to rotate, but it is able to swing a little. It is held back by a spiral spring. The amount the ring can swing depends on the strength of the torque.

   Attached to the ring is a pointer which shows the speed of the vehicle on a suitable scale.

   The usual speedometer has a round dial, clearly marked with numbers in tens. Another type has a revolving drum, to which the scale is attached. When the speed increases, the drum turns, and the speed change is shown on the scale through a narrow gap in a panel fixed in front of the scale. The scale may take the form of a coloured band.

   Usually, a speedometer is combined with an odometer, which records the distance travelled. The odometer is driven by the same drive shaft or cable that drives the magnet. The movement of the speedometer shaft is transmitted through a system of gears to the distance recorder. This recorder actually counts the number of revolutions made by the vehicle's front wheels. Because a certain number of revolutions are equal to a certain distance travelled by the vehicle, the odometer can be made to give a direct reading of the distance covered.

   When the disc that counts the 'units' has made one revolution, the counting disc for the 'tens' is moved on one place. When the 'tens' disc has made one revolution, it then moves the 'hundreds' disc on one place. This process is repeated up to the 'ten thousands' disc.

Flowmeter

   A flowmeter is a device that measures the rate of flow of a liquid or a gas. The commonest flowmeter is called an orifice meter.
   An orifice meter is an obstruction placed in the pipe through which the liquid or gas is passing. As the liquid or gas passes the orifice, its speed is temporarily changed; as a result the pressure it exerts on the walls of the pipe is also changed. By measuring this pressure at, and on both sides of, the orifice, the rate of flow may be computed.
   Other flowmeters include the shunt meter, which directs part of the flow past a propeller, and the rotameter.

What is a fluorescent lamp?

   A fluorescent lamp is a source of artificial light produced by bombarding a phosphor with ultraviolet light. The phosphor is the heart of the lamp, for it converts shortwave ultraviolet radiation into visible light. (A phosphor, by definition, is a substance that gives off light when struck by suitable radiation, usually ultraviolet light.)
   Fluorescent lamps for household use are available in a number of different colors. Compounds of calcium, sulfur, phosphorus, and other materials are carefully mixed to produce light of daylight quality or various tints.
   A fluorescent lamp is made in the shape of a tube, the inner wall of which is coated with the phosphor. The tube is usually filled with argon, with a small amount of mercury; the amount of mercury and the pressure are adjusted to produce a considerable amount of ultraviolet radiation at 2,537 angstrom units wavelength; this is a frequency that is efficient in causing fluorescence in the phosphor materials used. At each end of the tube is an electrode. When electrons are made to flow between the electrodes by a proper voltage of electric current, the mercury vapor produces ultraviolet radiation. This radiation, in turn, makes the phosphor coating give off visible light.

What is an incubator?

   A chicken egg in order to hatch must be kept warm. A mother hen sits on her eggs to hatch them. Her body keeps them just warm enough. But many little chickens are hatched from eggs that were kept warm in a different way. The eggs were kept warm in an incubator. Ducks and turkeys and even game birds are sometimes hatched in incubators, too.

   An incubator is a kind of oven. The first incubators were heated with oil lamps and had to be watched carefully. There was danger that they would get too warm or too cool. Most incubators today are heated with electricity. It is easy to keep them at an even temperature. For chickens, the temperature should be kept at about  102 °F. The eggs are turned from time to time so that they are heated evenly all over. The air inside the incubator must be kept fresh and moist as well as warm.

   Incubators of another kind are found in hospitals. They are for babies that are especially tiny and weak when they are born. These babies need to be kept as warm as they were when they were still in their mothers' bodies. As a rule they are soon big and strong enough to leave the incubators. Incubators, now that they are in common use in hospitals, are saving the lives of a great many babies.