The housefly is a fly of the suborder Cyclorrhapha. It is believed to have evolved in the Cenozoic era in the Middle East, has spread all over the world as a commensal of humans, it is the most common fly species found in houses. Adults are grey to black, with four dark, longitudinal lines on the thorax hairy bodies, a single pair of membranous wings, they have red eyes, set farther apart in the larger female. The female housefly mates only once and stores the sperm for use, she lays batches of about 100 eggs on decaying organic matter such as food waste, carrion, or faeces. These soon hatch into legless white larvae, known as maggots. After 2 to 5 days of development, these metamorphose into reddish-brown pupae, about 8 mm long. Adult flies live for 2 to 4 weeks, but can hibernate during the winter; the adults feed on a variety of liquid or semiliquid substances, as well as solid materials which have been softened by their saliva. They can carry pathogens on their bodies and in their faeces, contaminate food, contribute to the transfer of food-borne illnesses, while, in numbers, they can be physically annoying.
For these reasons, they are considered pests. Houseflies have been used in the laboratory in research into sex determination. Flies appear in literature from Ancient Greek myth and Aesop's The Impertinent Insect onwards. Authors sometimes choose the fly to speak of the brevity of life, as in William Blake's 1794 poem "The Fly", which deals with mortality subject to uncontrollable circumstances. Adult houseflies are 6 to 7 mm long with a wingspan of 13 to 15 mm; the females tend to be larger winged than males, while males have longer legs. Females tend to vary more in size and there is geographic variation with larger individuals in higher latitudes; the head is convex in front and flat and conical behind. The pair of large compound eyes touch in the male, but are more separated in the female, they have a pair of short antennae. Flies process visual information around seven times more than humans, enabling them to identify and avoid attempts to catch or swat them, since they see the human's movements in slow motion with their higher flicker fusion rate.
The mouthparts are specially adapted for a liquid diet. This is a sponge-like structure, characterised by many grooves, called pseudotracheae, which suck up fluids by capillary action, it is used to distribute saliva to soften solid foods or collect loose particles. Houseflies have chemoreceptors, organs of taste, on the tarsi of their legs, so they can identify foods such as sugars by walking over them. Flies are seen cleaning their legs by rubbing them together, enabling the chemoreceptors to taste afresh whatever they walk on next. At the end of each leg is a pair of claws, below them are two adhesive pads, enabling the fly to walk up smooth walls and ceilings using Van der Waals forces; the claws help the fly to unstick the foot for the next step. Flies walk with a common gait on horizontal and vertical surfaces with three legs in contact with the surface and three in movement. On inverted surfaces, they alter the gait to keep four feet stuck to the surface. Flies land on a ceiling by flying straight towards it.
The thorax is a shade of gray, sometimes black, with four dark, longitudinal bands of width on the dorsal surface. The whole body is covered with short hairs. Like other Diptera, houseflies have only one pair of wings; the wings are translucent with a yellowish tinge at their base. Characteristically, the medial vein shows a sharp upward bend; each wing has a lobe at the calypter, covering the haltere. The abdomen irregular dark markings at the side, it has 10 segments. In males, the ninth segment bears a pair of claspers for copulation, the 10th bears anal cerci in both sexes. A variety of species around the world appear similar to the housefly, such as the lesser house fly, Fannia canicularis; the systematic identification of species may require the use of region-specific taxonomic keys and can require dissections of the male reproductive parts for confirmation. The housefly is the insect with the widest distribution in the world, it is present in the Arctic Circle, as well as in the tropics. It is present in all populated parts of Europe, Africa and the Americas.
Though the order of flies is much older, true houseflies are believed to have evolved in the beginning of the Cenozoic era. The housefly's superfamily, Muscoidea, is most related to the Oestroidea, more distantly to the Hippoboscoidea, they are thought to have originated in the southern Palearctic region the Middle East. Because of their close, commensal relationship with humans, they
Earth is the third planet from the Sun and the only astronomical object known to harbor life. According to radiometric dating and other sources of evidence, Earth formed over 4.5 billion years ago. Earth's gravity interacts with other objects in space the Sun and the Moon, Earth's only natural satellite. Earth revolves around the Sun in a period known as an Earth year. During this time, Earth rotates about its axis about 366.26 times. Earth's axis of rotation is tilted with respect to its orbital plane; the gravitational interaction between Earth and the Moon causes ocean tides, stabilizes Earth's orientation on its axis, slows its rotation. Earth is the largest of the four terrestrial planets. Earth's lithosphere is divided into several rigid tectonic plates that migrate across the surface over periods of many millions of years. About 71% of Earth's surface is covered with water by oceans; the remaining 29% is land consisting of continents and islands that together have many lakes and other sources of water that contribute to the hydrosphere.
The majority of Earth's polar regions are covered in ice, including the Antarctic ice sheet and the sea ice of the Arctic ice pack. Earth's interior remains active with a solid iron inner core, a liquid outer core that generates the Earth's magnetic field, a convecting mantle that drives plate tectonics. Within the first billion years of Earth's history, life appeared in the oceans and began to affect the Earth's atmosphere and surface, leading to the proliferation of aerobic and anaerobic organisms; some geological evidence indicates. Since the combination of Earth's distance from the Sun, physical properties, geological history have allowed life to evolve and thrive. In the history of the Earth, biodiversity has gone through long periods of expansion punctuated by mass extinction events. Over 99% of all species that lived on Earth are extinct. Estimates of the number of species on Earth today vary widely. Over 7.6 billion humans live on Earth and depend on its biosphere and natural resources for their survival.
Humans have developed diverse cultures. The modern English word Earth developed from a wide variety of Middle English forms, which derived from an Old English noun most spelled eorðe, it has cognates in every Germanic language, their proto-Germanic root has been reconstructed as *erþō. In its earliest appearances, eorðe was being used to translate the many senses of Latin terra and Greek γῆ: the ground, its soil, dry land, the human world, the surface of the world, the globe itself; as with Terra and Gaia, Earth was a personified goddess in Germanic paganism: the Angles were listed by Tacitus as among the devotees of Nerthus, Norse mythology included Jörð, a giantess given as the mother of Thor. Earth was written in lowercase, from early Middle English, its definite sense as "the globe" was expressed as the earth. By Early Modern English, many nouns were capitalized, the earth became the Earth when referenced along with other heavenly bodies. More the name is sometimes given as Earth, by analogy with the names of the other planets.
House styles now vary: Oxford spelling recognizes the lowercase form as the most common, with the capitalized form an acceptable variant. Another convention capitalizes "Earth" when appearing as a name but writes it in lowercase when preceded by the, it always appears in lowercase in colloquial expressions such as "what on earth are you doing?" The oldest material found in the Solar System is dated to 4.5672±0.0006 billion years ago. By 4.54±0.04 Bya the primordial Earth had formed. The bodies in the Solar System evolved with the Sun. In theory, a solar nebula partitions a volume out of a molecular cloud by gravitational collapse, which begins to spin and flatten into a circumstellar disk, the planets grow out of that disk with the Sun. A nebula contains gas, ice grains, dust. According to nebular theory, planetesimals formed by accretion, with the primordial Earth taking 10–20 million years to form. A subject of research is the formation of some 4.53 Bya. A leading hypothesis is that it was formed by accretion from material loosed from Earth after a Mars-sized object, named Theia, hit Earth.
In this view, the mass of Theia was 10 percent of Earth, it hit Earth with a glancing blow and some of its mass merged with Earth. Between 4.1 and 3.8 Bya, numerous asteroid impacts during the Late Heavy Bombardment caused significant changes to the greater surface environment of the Moon and, by inference, to that of Earth. Earth's atmosphere and oceans were formed by volcanic outgassing. Water vapor from these sources condensed into the oceans, augmented by water and ice from asteroids and comets. In this model, atmospheric "greenhouse gases" kept the oceans from freezing when the newly forming Sun had only 70% of its current luminosity. By 3.5 Bya, Earth's magnetic field was established, which helped prevent the atmosphere from being stripped away by the solar wind. A crust formed; the two models that explain land mass propose either a steady growth to the present-day forms or, more a rapid growth early in Earth history followed by a long-term steady continental area. Continents formed by plate tectonics
A camera is an optical instrument to capture still images or to record moving images, which are stored in a physical medium such as in a digital system or on photographic film. A camera consists of a lens which focuses light from the scene, a camera body which holds the image capture mechanism; the still image camera is the main instrument in the art of photography and captured images may be reproduced as a part of the process of photography, digital imaging, photographic printing. The similar artistic fields in the moving image camera domain are film and cinematography; the word camera comes from camera obscura, which means "dark chamber" and is the Latin name of the original device for projecting an image of external reality onto a flat surface. The modern photographic camera evolved from the camera obscura; the functioning of the camera is similar to the functioning of the human eye. The first permanent photograph was made in 1825 by Joseph Nicéphore Niépce. A camera works with the light of the visible spectrum or with other portions of the electromagnetic spectrum.
A still camera is an optical device which creates a single image of an object or scene and records it on an electronic sensor or photographic film. All cameras use the same basic design: light enters an enclosed box through a converging/convex lens and an image is recorded on a light-sensitive medium. A shutter mechanism controls the length of time. Most photographic cameras have functions that allow a person to view the scene to be recorded, allow for a desired part of the scene to be in focus, to control the exposure so that it is not too bright or too dim. On most digital cameras a display a liquid crystal display, permits the user to view the scene to be recorded and settings such as ISO speed and shutter speed. A movie camera or a video camera operates to a still camera, except it records a series of static images in rapid succession at a rate of 24 frames per second; when the images are combined and displayed in order, the illusion of motion is achieved. Traditional cameras capture light onto photographic film.
Video and digital cameras use an electronic image sensor a charge coupled device or a CMOS sensor to capture images which can be transferred or stored in a memory card or other storage inside the camera for playback or processing. Cameras that capture many images in sequence are known as movie cameras or as ciné cameras in Europe; however these categories overlap as still cameras are used to capture moving images in special effects work and many modern cameras can switch between still and motion recording modes. A wide range of film and plate formats have been used by cameras. In the early history plate sizes were specific for the make and model of camera although there developed some standardisation for the more popular cameras; the introduction of roll film drove the standardization process still further so that by the 1950s only a few standard roll films were in use. These included 120 film providing 8, 12 or 16 exposures, 220 film providing 16 or 24 exposures, 127 film providing 8 or 12 exposures and 135 providing 12, 20 or 36 exposures – or up to 72 exposures in the half-frame format or in bulk cassettes for the Leica Camera range.
For cine cameras, film 35 mm wide and perforated with sprocket holes was established as the standard format in the 1890s. It was used for nearly all film-based professional motion picture production. For amateur use, several smaller and therefore less expensive formats were introduced. 17.5 mm film, created by splitting 35 mm film, was one early amateur format, but 9.5 mm film, introduced in Europe in 1922, 16 mm film, introduced in the US in 1923, soon became the standards for "home movies" in their respective hemispheres. In 1932, the more economical 8 mm format was created by doubling the number of perforations in 16 mm film splitting it after exposure and processing; the Super 8 format, still 8 mm wide but with smaller perforations to make room for larger film frames, was introduced in 1965. Traditionally used to "tell the camera" the film speed of the selected film on film cameras, film speed numbers are employed on modern digital cameras as an indication of the system's gain from light to numerical output and to control the automatic exposure system.
Film speed is measured via the ISO system. The higher the film speed number the greater the film sensitivity to light, whereas with a lower number, the film is less sensitive to light. On digital cameras, electronic compensation for the color temperature associated with a given set of lighting conditions, ensuring that white light is registered as such on the imaging chip and therefore that the colors in the frame will appear natural. On mechanical, film-based cameras, this function is served by the operator's choice of film stock or with color correction filters. In addition to using white balance to register natural coloration of the image, photographers may employ white balance to aesthetic end, for example, white balancing to a blue object in order to obtain a warm color temperature; the lens of a camera brings it to a focus on the sensor. The design and manufacture of the lens is critical to the quality of the photograph being taken; the technological revolution in camera design in the 19th century revolutionized optical glass manufacture and lens design with great benefits for modern lens manufacture in a wide range of optical instruments from reading glasses to microscopes.
Pioneers included Leitz. Camera lenses are
Frequency is the number of occurrences of a repeating event per unit of time. It is referred to as temporal frequency, which emphasizes the contrast to spatial frequency and angular frequency; the period is the duration of time of one cycle in a repeating event, so the period is the reciprocal of the frequency. For example: if a newborn baby's heart beats at a frequency of 120 times a minute, its period—the time interval between beats—is half a second. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio signals, radio waves, light. For cyclical processes, such as rotation, oscillations, or waves, frequency is defined as a number of cycles per unit time. In physics and engineering disciplines, such as optics and radio, frequency is denoted by a Latin letter f or by the Greek letter ν or ν; the relation between the frequency and the period T of a repeating event or oscillation is given by f = 1 T.
The SI derived unit of frequency is the hertz, named after the German physicist Heinrich Hertz. One hertz means. If a TV has a refresh rate of 1 hertz the TV's screen will change its picture once a second. A previous name for this unit was cycles per second; the SI unit for period is the second. A traditional unit of measure used with rotating mechanical devices is revolutions per minute, abbreviated r/min or rpm. 60 rpm equals one hertz. As a matter of convenience and slower waves, such as ocean surface waves, tend to be described by wave period rather than frequency. Short and fast waves, like audio and radio, are described by their frequency instead of period; these used conversions are listed below: Angular frequency denoted by the Greek letter ω, is defined as the rate of change of angular displacement, θ, or the rate of change of the phase of a sinusoidal waveform, or as the rate of change of the argument to the sine function: y = sin = sin = sin d θ d t = ω = 2 π f Angular frequency is measured in radians per second but, for discrete-time signals, can be expressed as radians per sampling interval, a dimensionless quantity.
Angular frequency is larger than regular frequency by a factor of 2π. Spatial frequency is analogous to temporal frequency, but the time axis is replaced by one or more spatial displacement axes. E.g.: y = sin = sin d θ d x = k Wavenumber, k, is the spatial frequency analogue of angular temporal frequency and is measured in radians per meter. In the case of more than one spatial dimension, wavenumber is a vector quantity. For periodic waves in nondispersive media, frequency has an inverse relationship to the wavelength, λ. In dispersive media, the frequency f of a sinusoidal wave is equal to the phase velocity v of the wave divided by the wavelength λ of the wave: f = v λ. In the special case of electromagnetic waves moving through a vacuum v = c, where c is the speed of light in a vacuum, this expression becomes: f = c λ; when waves from a monochrome source travel from one medium to another, their frequency remains the same—only their wavelength and speed change. Measurement of frequency can done in the following ways, Calculating the frequency of a repeating event is accomplished by counting the number of times that event occurs within a specific time period dividing the count by the length of the time period.
For example, if 71 events occur within 15 seconds the frequency is: f = 71 15 s ≈ 4.73 Hz If the number of counts is not large, it is more accurate to measure the time interval for a predetermined number of occurrences, rather than the number of occurrences within a specified time. The latter method introduces a random error into the count of between zero and one count, so on average half a count; this is called gating error and causes an average error in the calculated frequency of Δ f = 1 2 T
In photography, shutter speed or exposure time is the length of time when the film or digital sensor inside the camera is exposed to light when a camera's shutter is open when taking a photograph. The amount of light that reaches the film or image sensor is proportional to the exposure time. 1⁄500 of a second will let half as much light in as 1⁄250. The camera's shutter speed, the lens's aperture, the Film Speed, the scene's luminance together determine the amount of light that reaches the film or sensor. Exposure value is a quantity that accounts for the f-number. Once the sensitivity to light of the recording surface is set in numbers expressed in "ISOs", the light emitted by the scene photographed can be controlled through aperture and shutter-speed to match the film or sensor sensitivity to light; this will achieve a good exposure. Too much light let into the camera results in an overly pale image while too little light will result in an overly dark image. Multiple combinations of shutter speed and f-number can give the same exposure value.
According to exposure value formula, doubling the exposure time doubles the amount of light. Reducing the aperture size at multiples of one over the square root of two lets half as much light into the camera at a predefined scale of f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, so on. For example, f/8 lets 4 times more light into the camera. A shutter speed of 1⁄50 s with an f/4 aperture gives the same exposure value as a 1⁄100 s shutter speed with an f/2.8 aperture, the same exposure value as a 1⁄200 s shutter speed with an f/2 aperture, or 1⁄25 s at f/5.6. In addition to its effect on exposure, the shutter speed changes the way movement appears in photographs. Short shutter speeds can be used to freeze fast-moving subjects, for example at sporting events. Long shutter speeds are used to intentionally blur a moving subject for effect. Short exposure times are sometimes called "fast", long exposure times "slow". Adjustments to the aperture need to be compensated by changes of the shutter speed to keep the same exposure.
In early days of photography, available shutter speeds were not standardized, though a typical sequence might have been 1⁄10 s, 1⁄25 s, 1⁄50 s, 1⁄100 s, 1⁄200 s and 1⁄500 s. Soon this problem resulted in a solution consisting in the adoption of a standardized way of choosing aperture so that each major step doubled or halved the amount of light entering the camera, a standardized 2:1 scale was adopted for shutter speed so that opening one aperture stop and reducing the amount of time of the shutter speed by one step resulted in the identical exposure; the agreed standards for shutter speeds are: With this scale, each increment doubles the amount of light or halves it. Camera shutters include one or two other settings for making long exposures: B keeps the shutter open as long as the shutter release is held. T keeps the shutter open; the ability of the photographer to take images without noticeable blurring by camera movement is an important parameter in the choice of the slowest possible shutter speed for a handheld camera.
The rough guide used by most 35 mm photographers is that the slowest shutter speed that can be used without much blur due to camera shake is the shutter speed numerically closest to the lens focal length. For example, for handheld use of a 35 mm camera with a 50 mm normal lens, the closest shutter speed is 1⁄60 s, while for a 200 mm lens it is recommended not to choose shutter speeds below 1⁄200 of a second; this rule can be augmented with knowledge of the intended application for the photograph, an image intended for significant enlargement and closeup viewing would require faster shutter speeds to avoid obvious blur. Through practice and special techniques such as bracing the camera, arms, or body to minimize camera movement, using a monopod or a tripod, slower shutter speeds can be used without blur. If a shutter speed is too slow for hand holding, a camera support a tripod, must be used. Image stabilization on digital cameras or lenses can permit the use of shutter speeds 3–4 stops slower.
Shutter priority refers to a shooting mode used in cameras. It allows the photographer to choose a shutter speed setting and allow the camera to decide the correct aperture; this is sometimes referred to as Shutter Speed Priority Auto Exposure, or TV mode, S mode on Nikons and most other brands. Shutter speed is one of several methods used to control the amount of light recorded by the camera's digital sensor or film, it is used to manipulate the visual effects of the final image. Slower shutter speeds are selected to suggest the movement of an object in a still photograph. Excessively fast shutter speeds can cause a moving subject to appear unnaturally frozen. For instance, a running person may be caught with both feet in the air with all indication of movement lost in the frozen moment; when a slower shutter speed is selected, a longer time passes from the moment the shutter opens till the moment it closes. More time is available for movement in the subject to be recorded by the camera as a blur.
A slower shutter speed will allow the photographer to introd
The human eye is an organ which reacts to light and pressure. As a sense organ, the mammalian eye allows vision. Human eyes help to provide a three dimensional, moving image coloured in daylight. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth; the human eye can differentiate between about 10 million colors and is capable of detecting a single photon. Similar to the eyes of other mammals, the human eye's non-image-forming photosensitive ganglion cells in the retina receive light signals which affect adjustment of the size of the pupil and suppression of the hormone melatonin and entrainment of the body clock; the eye is not shaped like a perfect sphere, rather it is a fused two-piece unit, composed of the anterior segment and the posterior segment. The anterior segment is made up of the cornea and lens; the cornea is transparent and more curved, is linked to the larger posterior segment, composed of the vitreous, retina and the outer white shell called the sclera.
The cornea is about 11.5 mm in diameter, 1/2 mm in thickness near its center. The posterior chamber constitutes the remaining five-sixths; the cornea and sclera are connected by an area termed the limbus. The iris is the pigmented circular structure concentrically surrounding the center of the eye, the pupil, which appears to be black; the size of the pupil, which controls the amount of light entering the eye, is adjusted by the iris' dilator and sphincter muscles. Light energy enters the eye through the cornea, through the pupil and through the lens; the lens shape is controlled by the ciliary muscle. Photons of light falling on the light-sensitive cells of the retina are converted into electrical signals that are transmitted to the brain by the optic nerve and interpreted as sight and vision. Dimensions differ among adults by only one or two millimetres, remarkably consistent across different ethnicities; the vertical measure less than the horizontal, is about 24 mm. The transverse size of a human adult eye is 24.2 mm and the sagittal size is 23.7 mm with no significant difference between sexes and age groups.
Strong correlation has been found between the width of the orbit. The typical adult eye has an anterior to posterior diameter of 24 millimetres, a volume of six cubic centimetres, a mass of 7.5 grams.. The eyeball grows increasing from about 16–17 millimetres at birth to 22.5–23 mm by three years of age. By age 12, the eye attains its full size; the eye is made up of layers, enclosing various anatomical structures. The outermost layer, known as the fibrous tunic, is composed of the sclera; the middle layer, known as the vascular tunic or uvea, consists of the choroid, ciliary body, pigmented epithelium and iris. The innermost is the retina, which gets its oxygenation from the blood vessels of the choroid as well as the retinal vessels; the spaces of the eye are filled with the aqueous humour anteriorly, between the cornea and lens, the vitreous body, a jelly-like substance, behind the lens, filling the entire posterior cavity. The aqueous humour is a clear watery fluid, contained in two areas: the anterior chamber between the cornea and the iris, the posterior chamber between the iris and the lens.
The lens is suspended to the ciliary body by the suspensory ligament, made up of hundreds of fine transparent fibers which transmit muscular forces to change the shape of the lens for accommodation. The vitreous body is a clear substance composed of water and proteins, which give it a jelly-like and sticky composition; the approximate field of view of an individual human eye varies by facial anatomy, but is 30° superior, 45° nasal, 70° inferior, 100° temporal. For both eyes combined visual field is 200 ° horizontal, it is 13700 square degrees for binocular vision. When viewed at large angles from the side, the iris and pupil may still be visible by the viewer, indicating the person has peripheral vision possible at that angle. About 15° temporal and 1.5° below the horizontal is the blind spot created by the optic nerve nasally, 7.5° high and 5.5° wide. The retina has a static contrast ratio of around 100:1; as soon as the eye moves to acquire a target, it re-adjusts its exposure by adjusting the iris, which adjusts the size of the pupil.
Initial dark adaptation takes place in four seconds of profound, uninterrupted darkness. The process is nonlinear and multifaceted, so an interruption by light exposure requires restarting the dark adaptation process over again. Full adaptation is dependent on good blood flow; the human eye can detect a luminance range of 1014, or one hundred trillion, from 10−6 cd/m2, or one millionth of a candela per square meter to 108 cd/m2 or one hundred million candelas per square meter. This range does not include looking at the midday lightning discharge. At the low end o
Electrification is the process of powering by electricity and, in many contexts, the introduction of such power by changing over from an earlier power source. The broad meaning of the term, such as in the history of technology, economic history, economic development applies to a region or national economy. Broadly speaking, electrification was the build-out of the electricity generation and electric power distribution systems that occurred in Britain, the United States, other now-developed countries from the mid-1880s until around 1950 and is still in progress in rural areas in some developing countries; this included the transition in manufacturing from line shaft and belt drive using steam engines and water power to electric motors. The electrification of particular sectors of the economy is called by terms such as factory electrification, household electrification, rural electrification or railway electrification, it may apply to changing industrial processes such as smelting, separating or refining from coal or coke heating, or chemical processes to some type of electric process such as electric arc furnace, electric induction or resistance heating, or electrolysis or electrolytic separating.
Electrification was called "the greatest engineering achievement of the 20th Century" by the National Academy of Engineering. The earliest commercial uses of electricity were the telegraph. In the years of 1831–1832, Michael Faraday discovered the operating principle of electromagnetic generators; the principle called Faraday's law, is that an electromotive force is generated in an electrical conductor, subjected to a varying magnetic flux, as for example, a wire moving through a magnetic field. He built the first electromagnetic generator, called the Faraday disk, a type of homopolar generator, using a copper disc rotating between the poles of a horseshoe magnet, it produced a small DC voltage. Around 1832, Hippolyte Pixii improved the magneto by using a wire wound horseshoe, with the extra coils of conductor generating more current, but it was AC. André-Marie Ampère suggested a means of converting current from Pixii's magneto to DC using a rocking switch. Segmented commutators were used to produce direct current.
William Fothergill Cooke and Charles Wheatstone developed a telegraph around 1838-40. In 1840 Wheatstone was using a magneto. Wheatstone and Cooke made an important improvement in electrical generation by using a battery-powered electromagnet in place of a permanent magnet, which they patented in 1845; the self-excited magnetic field dynamo did away with the battery to power electromagnets. This type of dynamo was made by several people in 1866; the first practical generator, the Gramme machine was made by Z. T Gramme, who sold many of these machines in the 1870s. British engineer R. E. B. Crompton made other mechanical improvements. Compound winding, which gave more stable voltage with load, improved operating characteristics of generators; the improvements in electrical generation technology increased the efficiency and reliability in the 19th century. The first magnetos only converted a few percent of mechanical energy to electricity. By the end of the 19th century the highest efficiencies were over 90%.
Sir Humphry Davy invented the carbon arc lamp in 1802 upon discovering that electricity could produce a light arc with carbon electrodes. However, it was not used to any great extent until a practical means of generating electricity was developed. Carbon arc lamps were started by making contact between two carbon electrodes, which were separated to within a narrow gap; because the carbon burned away, the gap had to be readjusted. Several mechanisms were developed to regulate the arc. A common approach was to feed a carbon electrode by gravity and maintain the gap with a pair of electromagnets, one of which retracted the upper carbon after the arc was started and the second controlled a brake on the gravity feed. Arc lamps of the time had intense light output – in the range of 4000 candlepower – and released a lot of heat, they were a fire hazard, all of which made them inappropriate for lighting homes. In the 1850s, many of these problems were solved by the arc lamp invented by William Petrie and William Staite.
The lamp used a magneto-electric generator and had a self-regulating mechanism to control the gap between the two carbon rods. Their light was a great novelty at the time; these arc lamps and designs similar to it, powered by large magnetos, were first installed on English lighthouses in the mid 1850s, but the power limitations prevented these models from being a proper success. The first successful arc lamp was developed by Russian engineer Pavel Yablochkov, used the Gramme generator, its advantage lay in the fact that it didn't require the use of a mechanical regulator like its predecessors. It was first exhibited at the Paris Exposition of 1878 and was promoted by Gramme; the arc light was installed along the half mile length of Avenue de l'Opéra, Place du Theatre Francais and around the Place de l'Opéra in 1878. British engineer R. E. B. Crompton developed a more sophisticated design in 1878 which gave a much brighter and steadier light than the Yablochkov candle. In 1878, he formed Crompton & Co. and began to manufacture and install the Crompton lamp.
His concern was one of the first electrical engineering firms in the world. Various forms of incandescent light bulbs had numerous inventors; these were invented by Joseph Swan in 1878 in Britain and by Thomas Edison in 1879 in the US. E