Watch
A watch is a timepiece intended to be carried or worn by a person. It is designed to keep working despite the motions caused by the person's activities. A wristwatch is designed to be worn around the wrist, attached by a watch strap or other type of bracelet. A pocket watch is designed for a person to carry in a pocket; the study of timekeeping is known as horology. Watches progressed in the 17th century from spring-powered clocks, which appeared as early as the 14th century. During most of its history the watch was a mechanical device, driven by clockwork, powered by winding a mainspring, keeping time with an oscillating balance wheel; these are called mechanical watches. In the 1960s the electronic quartz watch was invented, powered by a battery and kept time with a vibrating quartz crystal. By the 1980s the quartz watch had taken over most of the market from the mechanical watch; this is called the quartz revolution. Developments in the 2010s include smartwatches, which are elaborate computer-like electronic devices designed to be worn on a wrist.
They incorporate timekeeping functions, but these are only a small subset of the smartwatch's facilities. In general, modern watches display the day, date and year. For mechanical watches, various extra features called "complications", such as moon-phase displays and the different types of tourbillon, are sometimes included. Most electronic quartz watches, on the other hand, include time-related features such as timers and alarm functions. Furthermore, some modern smartwatches incorporate calculators, GPS and Bluetooth technology or have heart-rate monitoring capabilities, some of them use radio clock technology to correct the time. Today, most watches in the market that are inexpensive and medium-priced, used for timekeeping, have quartz movements. However, expensive collectible watches, valued more for their elaborate craftsmanship, aesthetic appeal and glamorous design than for simple timekeeping have traditional mechanical movements though they are less accurate and more expensive than electronic ones.
As of 2018, the most expensive watch sold at auction is the Patek Philippe Henry Graves Supercomplication, the world's most complicated mechanical watch until 1989, fetching 24 million US dollars in Geneva on November 11, 2014. Watches evolved from portable spring-driven clocks. Watches were not worn in pockets until the 17th century. One account says that the word "watch" came from the Old English word woecce which meant "watchman", because it was used by town watchmen to keep track of their shifts at work. Another says that the term came from 17th century sailors, who used the new mechanisms to time the length of their shipboard watches. A great leap forward in accuracy occurred in 1657 with the addition of the balance spring to the balance wheel, an invention disputed both at the time and since between Robert Hooke and Christiaan Huygens; this innovation increased watches' accuracy enormously, reducing error from several hours per day to 10 minutes per day, resulting in the addition of the minute hand to the face from around 1680 in Britain and 1700 in France.
The increased accuracy of the balance wheel focused attention on errors caused by other parts of the movement, igniting a two-century wave of watchmaking innovation. The first thing to be improved was the escapement; the verge escapement was replaced in quality watches by the cylinder escapement, invented by Thomas Tompion in 1695 and further developed by George Graham in the 1720s. Improvements in manufacturing such as the tooth-cutting machine devised by Robert Hooke allowed some increase in the volume of watch production, although finishing and assembling was still done by hand until well into the 19th century. A major cause of error in balance wheel timepieces, caused by changes in elasticity of the balance spring from temperature changes, was solved by the bimetallic temperature compensated balance wheel invented in 1765 by Pierre Le Roy and improved by Thomas Earnshaw; the lever escapement was the single most important technological breakthrough, was invented by Thomas Mudge in 1759 and improved by Josiah Emery in 1785, although it only came into use from about 1800 onwards, chiefly in Britain.
The British had predominated in watch manufacture for much of the 17th and 18th centuries, but maintained a system of production, geared towards high-quality products for the elite. Although there was an attempt to modernise clock manufacture with mass production techniques and the application of duplicating tools and machinery by the British Watch Company in 1843, it was in the United States that this system took off. Aaron Lufkin Dennison started a factory in 1851 in Massachusetts that used interchangeable parts, by 1861 it was running a successful enterprise incorporated as the Waltham Watch Company; the concept of the wristwatch goes back to the production of the earliest watches in the 16th century. Elizabeth I of England received a wristwatch from Robert Dudley in 1571, described as an armed watch; the oldest surviving wristwatch is one given to Joséphine de Beauharnais. From the beginning, wristwatches were exclusively worn by women, while men used pocket watches up until the early 20th century.
Wristwatches were first worn by military men towards the end of the 19th century, when the importance of synchronizing maneuvers during war, without revealing the plan to the enemy through signaling, was recognized. The Garstin Company of London patented a "Watch Wristlet" design in 1893, but they were producing similar designs from the 1880s
Machine
A machine is a mechanical structure that uses power to apply forces and control movement to perform an intended action. Machines can be driven by animals and people, by natural forces such as wind and water, by chemical, thermal, or electrical power, include a system of mechanisms that shape the actuator input to achieve a specific application of output forces and movement, they can include computers and sensors that monitor performance and plan movement called mechanical systems. Renaissance natural philosophers identified six simple machines which were the elementary devices that put a load into motion, calculated the ratio of output force to input force, known today as mechanical advantage. Modern machines are complex systems that consist of structural elements and control components and include interfaces for convenient use. Examples include a wide range of vehicles, such as automobiles and airplanes, appliances in the home and office, including computers, building air handling and water handling systems, as well as farm machinery, machine tools and factory automation systems and robots.
The English word machine comes through Middle French from Latin machina, which in turn derives from the Greek. The word mechanical comes from the same Greek roots. A wider meaning of "fabric, structure" is found in classical Latin, but not in Greek usage; this meaning is found in late medieval French, is adopted from the French into English in the mid-16th century. In the 17th century, the word could mean a scheme or plot, a meaning now expressed by the derived machination; the modern meaning develops out of specialized application of the term to stage engines used in theater and to military siege engines, both in the late 16th and early 17th centuries. The OED traces the formal, modern meaning to John Harris' Lexicon Technicum, which has: Machine, or Engine, in Mechanicks, is whatsoever hath Force sufficient either to raise or stop the Motion of a Body... Simple Machines are reckoned to be Six in Number, viz. the Ballance, Pulley, Wheel and Screw... Compound Machines, or Engines, are innumerable.
The word engine used as a synonym both by Harris and in language derives from Latin ingenium "ingenuity, an invention". The hand axe, made by chipping flint to form a wedge, in the hands of a human transforms force and movement of the tool into a transverse splitting forces and movement of the workpiece; the idea of a simple machine originated with the Greek philosopher Archimedes around the 3rd century BC, who studied the Archimedean simple machines: lever and screw. Archimedes discovered the principle of mechanical advantage in the lever. Greek philosophers defined the classic five simple machines and were able to calculate their mechanical advantage. Heron of Alexandria in his work Mechanics lists five mechanisms that can "set a load in motion". However, the Greeks' understanding was limited to statics and did not include dynamics or the concept of work. During the Renaissance the dynamics of the Mechanical Powers, as the simple machines were called, began to be studied from the standpoint of how much useful work they could perform, leading to the new concept of mechanical work.
In 1586 Flemish engineer Simon Stevin derived the mechanical advantage of the inclined plane, it was included with the other simple machines. The complete dynamic theory of simple machines was worked out by Italian scientist Galileo Galilei in 1600 in Le Meccaniche, he was the first to understand that simple machines do not create energy, they transform it. The classic rules of sliding friction in machines were discovered by Leonardo da Vinci, but remained unpublished in his notebooks, they were rediscovered by Guillaume Amontons and were further developed by Charles-Augustin de Coulomb. James Watt patented his parallel motion linkage in 1782, which made the double acting steam engine practical; the Boulton and Watt steam engine and designs powered steam locomotives, steam ships, factories. The Industrial Revolution was a period from 1750 to 1850 where changes in agriculture, mining and technology had a profound effect on the social and cultural conditions of the times, it began in the United Kingdom subsequently spread throughout Western Europe, North America and the rest of the world.
Starting in the part of the 18th century, there began a transition in parts of Great Britain's manual labour and draft-animal-based economy towards machine-based manufacturing. It started with the mechanisation of the textile industries, the development of iron-making techniques and the increased use of refined coal; the idea that a machine can be decomposed into simple movable elements led Archimedes to define the lever and screw as simple machines. By the time of the Renaissance this list increased to include the wheel and axle and inclined plane; the modern approach to characterizing machines focusses on the components that allow movement, known as joints. Wedge: Perhaps the first example of a device designed to manage power is the hand axe called biface and Olorgesailie. A hand axe is made by chipping stone flint, to form a bifacial edge, or wedge. A wedge is a simple machine that transforms lateral force and movement o
Robert Boyle
Robert Boyle was an Anglo-Irish natural philosopher, chemist and inventor. Boyle is regarded today as the first modern chemist, therefore one of the founders of modern chemistry, one of the pioneers of modern experimental scientific method, he is best known for Boyle's law, which describes the inversely proportional relationship between the absolute pressure and volume of a gas, if the temperature is kept constant within a closed system. Among his works, The Sceptical Chymist is seen as a cornerstone book in the field of chemistry, he is noted for his writings in theology. Boyle was born at Lismore Castle, in County Waterford, the seventh son and fourteenth child of The 1st Earl of Cork and Catherine Fenton. Lord Cork known as Richard Boyle, had arrived in Dublin from England in 1588 during the Tudor plantations of Ireland and obtained an appointment as a deputy escheator, he had amassed enormous wealth and landholdings by the time Robert was born, had been created Earl of Cork in October 1620.
Catherine Fenton, Countess of Cork, was the daughter of Sir Geoffrey Fenton, the former Secretary of State for Ireland, born in Dublin in 1539, Alice Weston, the daughter of Robert Weston, born in Lismore in 1541. As a child, Boyle was fostered to a local family. Boyle received private tutoring in Latin and French and when he was eight years old, following the death of his mother, he was sent to Eton College in England, his father's friend, Sir Henry Wotton, was the provost of the college. During this time, his father hired a private tutor, Robert Carew, who had knowledge of Irish, to act as private tutor to his sons in Eton. However, "only Mr. Robert sometimes desires it and is a little entered in it", but despite the "many reasons" given by Carew to turn their attentions to it, "they practice the French and Latin but they affect not the Irish". After spending over three years at Eton, Robert travelled abroad with a French tutor, they visited Italy in 1641 and remained in Florence during the winter of that year studying the "paradoxes of the great star-gazer" Galileo Galilei, elderly but still living in 1641.
Robert returned to England from continental Europe in mid-1644 with a keen interest in scientific research. His father, Lord Cork, had died the previous year and had left him the manor of Stalbridge in Dorset as well as substantial estates in County Limerick in Ireland that he had acquired. Robert made his residence at Stalbridge House, between 1644 and 1652, conducted many experiments there. From that time, Robert devoted his life to scientific research and soon took a prominent place in the band of enquirers, known as the "Invisible College", who devoted themselves to the cultivation of the "new philosophy", they met in London at Gresham College, some of the members had meetings at Oxford. Having made several visits to his Irish estates beginning in 1647, Robert moved to Ireland in 1652 but became frustrated at his inability to make progress in his chemical work. In one letter, he described Ireland as "a barbarous country where chemical spirits were so misunderstood and chemical instruments so unprocurable that it was hard to have any Hermetic thoughts in it."In 1654, Boyle left Ireland for Oxford to pursue his work more successfully.
An inscription can be found on the wall of University College, the High Street at Oxford, marking the spot where Cross Hall stood until the early 19th century. It was here that Boyle rented rooms from the wealthy apothecary. Reading in 1657 of Otto von Guericke's air pump, he set himself with the assistance of Robert Hooke to devise improvements in its construction, with the result, the "machina Boyleana" or "Pneumatical Engine", finished in 1659, he began a series of experiments on the properties of air. An account of Boyle's work with the air pump was published in 1660 under the title New Experiments Physico-Mechanical, Touching the Spring of the Air, its Effects. Among the critics of the views put forward in this book was a Jesuit, Francis Line, it was while answering his objections that Boyle made his first mention of the law that the volume of a gas varies inversely to the pressure of the gas, which among English-speaking people is called Boyle's Law after his name; the person who formulated the hypothesis was Henry Power in 1661.
Boyle in 1662 included a reference to a paper written by Power, but mistakenly attributed it to Richard Towneley. In continental Europe the hypothesis is sometimes attributed to Edme Mariotte, although he did not publish it until 1676 and was aware of Boyle's work at the time. In 1663 the Invisible College became The Royal Society of London for Improving Natural Knowledge, the charter of incorporation granted by Charles II of England named Boyle a member of the council. In 1680 he declined the honour from a scruple about oaths, he made a "wish list" of 24 possible inventions which included "the prolongation of life", the "art of flying", "perpetual light", "making armour light and hard", "a ship to sail with all winds, a ship not to be sunk", "practicable and certain way of finding longitudes", "potent drugs to alter or exalt imagination, waking and other functions and appease pain, procure innocent sleep, harmless dreams, etc." They are extraordinary. It was during his time at Oxford; the Chevaliers are thought to have been established by royal order a few years before Boyle's time at Oxford.
The early part
Photoreceptor cell
A photoreceptor cell is a specialized type of neuroepithelial cell found in the retina, capable of visual phototransduction. The great biological importance of photoreceptors is that they convert light into signals that can stimulate biological processes. To be more specific, photoreceptor proteins in the cell absorb photons, triggering a change in the cell's membrane potential. There are three known types of photoreceptor cells in mammalian eyes: rods and intrinsically photosensitive retinal ganglion cells; the two classic photoreceptor cells are rods and cones, each contributing information used by the visual system to form a representation of the visual world, sight. The rods are narrower than the cones and distributed differently across the retina, but the chemical process in each that supports phototransduction is similar. A third class of mammalian photoreceptor cell was discovered during the 1990s: the intrinsically photosensitive retinal ganglion cells; these cells do not contribute to sight directly, but are thought to support circadian rhythms and pupillary reflex.
There are major functional differences between the cones. Rods are sensitive, can be triggered by a single photon. At low light levels, visual experience is based on the rod signal. Cones require brighter light to produce a signal. In humans, there are three different types of cone cell, distinguished by their pattern of response to light of different wavelengths. Color experience is calculated from these three distinct signals via an opponent process; this explains why colors cannot be seen at low light levels, when only the rod and not the cone photoreceptor cells are active. The three types of cone cell respond to light of short and long wavelengths, so they may be referred to as S-cones, M-cones, L-cones. According to the principle of univariance, the firing of the cell depends upon only the number of photons absorbed; the different responses of the three types of cone cells are determined by the likelihoods that their respective photoreceptor proteins will absorb photons of different wavelengths.
So, for example, an L cone cell contains a photoreceptor protein that more absorbs long wavelengths of light. Light of a shorter wavelength can produce the same response, but it must be much brighter to do so; the human retina contains about 120 million rod cells, 6 million cone cells. The number and ratio of rods to cones varies among species, dependent on whether an animal is diurnal or nocturnal. Certain owls, such as the nocturnal tawny owl, have a tremendous number of rods in their retinae. In the human visual system, in addition to the photosensitive rods & cones, there are about 2.4 million to 3 million ganglion cells, with 1 to 2% of them being photosensitive. The axons of ganglion cells form the two optic nerves. Photoreceptor cells are arranged in an irregular but hexagonal grid, known as the retinal mosaic; the pineal and parapineal glands are photoreceptive in non-mammalian vertebrates, but not in mammals. Birds have photoactive cerebrospinal fluid -contacting neurons within the paraventricular organ that respond to light in the absence of input from the eyes or neurotransmitters.
Invertebrate photoreceptors in organisms such as insects and molluscs are different in both their morphological organization and their underlying biochemical pathways. This article describes human photoreceptors. Rod and cone photoreceptors are found on the outermost layer of the retina. Closest to the visual field is the axon terminal, which releases a neurotransmitter called glutamate to bipolar cells. Farther back is the cell body. Farther back still is a specialized part of the cell full of mitochondria; the chief function of the inner segment is to provide ATP for the sodium-potassium pump. Closest to the brain is the outer segment, the part of the photoreceptor that absorbs light. Outer segments are modified cilia that contain disks filled with opsin, the molecule that absorbs photons, as well as voltage-gated sodium channels; the membranous photoreceptor protein opsin contains. In rod cells, these together are called rhodopsin. In cone cells, there are different types of opsins that combine with retinal to form pigments called photopsins.
Three different classes of photopsins in the cones react to different ranges of light frequency, a differentiation that allows the visual system to calculate color. The function of the photoreceptor cell is to convert the light energy of the photon into a form of energy communicable to the nervous system and usable to the organism: This conversion is called signal transduction; the opsin found in the intrinsically photosensitive ganglion cells of the retina is called melanopsin. These cells are involved in various reflexive responses of the brain and body to the presence of light, such as the regulation of circadian rhythms, pupillary reflex and other non-visual responses to light. Melanopsin functionally resembles invertebrate opsins; when light activates the melanopsin signaling system, the melanopsin-containing ganglion cells discharge nerve impulses that are conducted through their axons to specific brain targets. These targets include the olivary pretectal nucleus, the LGN, through the retinohypothalamic tract, the suprachiasmatic nucleus of the hypothalamus.
Melanops
Altimeter
An altimeter or an altitude meter is an instrument used to measure the altitude of an object above a fixed level. The measurement of altitude is called altimetry, related to the term bathymetry, the measurement of depth under water. Altitude can be determined based on the measurement of atmospheric pressure; the greater the altitude, the lower the pressure. When a barometer is supplied with a nonlinear calibration so as to indicate altitude, the instrument is called a pressure altimeter or barometric altimeter. A pressure altimeter is the altimeter found in most aircraft, skydivers use wrist-mounted versions for similar purposes. Hikers and mountain climbers use wrist-mounted or hand-held altimeters, in addition to other navigational tools such as a map, magnetic compass, or GPS receiver; the calibration of an altimeter follows the equation z = c T log , where c is a constant, T is the absolute temperature, P is the pressure at altitude z, Po is the pressure at sea level. The constant c depends on the molar mass of the air.
However, one must be aware that this type of altimeter relies on "density altitude" and its readings can vary by hundreds of feet owing to a sudden change in air pressure, such as from a cold front, without any actual change in altitude. A barometric altimeter, used along with a topographic map, can help to verify one's location, it is more reliable, more accurate, than a GPS receiver for measuring altitude. Because barometric pressure changes with the weather, hikers must periodically re-calibrate their altimeters when they reach a known altitude, such as a trail junction or peak marked on a topographical map. An altimeter is the most important piece of skydiving equipment, after the parachute itself. Altitude awareness is crucial at all times during the jump, determines the appropriate response to maintain safety. Since altitude awareness is so important in skydiving, there is a wide variety of altimeter designs made for use in the sport, a non-student skydiver will use two or more altimeters in a single jump: Hand, wrist or chest-mounted mechanical analogue visual altimeters.
This is the most basic and common type, is used by all student skydivers. The common design has a face marked from 0 to 4000 m, on which an arrow points to the current altitude; the face plate sports sections prominently marked with yellow and red signifying the recommended deployment altitude, as well as emergency procedure decision altitude. A mechanical altimeter has a knob that needs to be manually adjusted to make it point to 0 on the ground before jump, if the landing spot is not at the same altitude as the takeoff spot, the user needs to adjust it appropriately; some advanced electronic altimeters are available which make use of the familiar analogue display, despite internally operating digitally. Digital visual altimeters, mounted on the wrist or hand; this type always operates electronically, conveys the altitude as a number, rather than a pointer on a dial. Since these altimeters contain all the electronic circuitry necessary for altitude calculation, they are equipped with auxiliary functions such as electronic logbook, real-time jump profile replay, speed indication, simulator mode for use in ground training, etc.
An electronic altimeter is activated on the ground before the jump, calibrates automatically to point to 0. It is thus essential that the user not turn it on earlier than necessary to avoid, for example, the drive to a dropzone located at a different altitude than one's home which could cause a fatal false reading. If the intended landing zone is at a different elevation than the takeoff point, the user needs to input the appropriate offset by using a designated function. Audible altimeters; these are inserted into one's helmet, emit a warning tone at a predefined altitude. Contemporary audibles have evolved from their crude beginnings, sport a vast array of functions, such as multiple tones at different altitudes, multiple saved profiles that can be switched electronic logbook with data transfer to a PC for analysis, distinct free fall and canopy modes with different warning altitudes, swoop approach guiding tones, etc. Audibles are auxiliary devices, do not replace, but complement a visual altimeter which remains the primary tool for maintaining altitude awareness.
The advent of modern skydiving disciplines such as freeflying, in which the ground might not be in one's field of view for long periods of time, has made the use of audibles nearly universal, all skydiving helmets come with one or more built-in ports in which an audible might be placed. Audibles are not recommended and banned from use by student skydivers, who need to build up a proper altitude awareness regime for themselves. Auxiliary visual altimeters; these do not show the precise altitude, but rather help maintain a general indicator in one's peripheral vision. They might either operate in tandem with an audible equipped with an appropriate port, in which case they emit warning flashes complementing the audible tones, or be standalone and use another display mode, such as showing either green or red light depending on the altitude. Speaking al
Light
Light is electromagnetic radiation within a certain portion of the electromagnetic spectrum. The word refers to visible light, the visible spectrum, visible to the human eye and is responsible for the sense of sight. Visible light is defined as having wavelengths in the range of 400–700 nanometres, or 4.00 × 10−7 to 7.00 × 10−7 m, between the infrared and the ultraviolet. This wavelength means a frequency range of 430–750 terahertz; the main source of light on Earth is the Sun. Sunlight provides the energy that green plants use to create sugars in the form of starches, which release energy into the living things that digest them; this process of photosynthesis provides all the energy used by living things. Another important source of light for humans has been fire, from ancient campfires to modern kerosene lamps. With the development of electric lights and power systems, electric lighting has replaced firelight; some species of animals generate their own light, a process called bioluminescence.
For example, fireflies use light to locate mates, vampire squids use it to hide themselves from prey. The primary properties of visible light are intensity, propagation direction, frequency or wavelength spectrum, polarization, while its speed in a vacuum, 299,792,458 metres per second, is one of the fundamental constants of nature. Visible light, as with all types of electromagnetic radiation, is experimentally found to always move at this speed in a vacuum. In physics, the term light sometimes refers to electromagnetic radiation of any wavelength, whether visible or not. In this sense, gamma rays, X-rays and radio waves are light. Like all types of EM radiation, visible light propagates as waves. However, the energy imparted by the waves is absorbed at single locations the way particles are absorbed; the absorbed energy of the EM waves is called a photon, represents the quanta of light. When a wave of light is transformed and absorbed as a photon, the energy of the wave collapses to a single location, this location is where the photon "arrives."
This is. This dual wave-like and particle-like nature of light is known as the wave–particle duality; the study of light, known as optics, is an important research area in modern physics. EM radiation, or EMR, is classified by wavelength into radio waves, infrared, the visible spectrum that we perceive as light, ultraviolet, X-rays, gamma rays; the behavior of EMR depends on its wavelength. Higher frequencies have shorter wavelengths, lower frequencies have longer wavelengths; when EMR interacts with single atoms and molecules, its behavior depends on the amount of energy per quantum it carries. EMR in the visible light region consists of quanta that are at the lower end of the energies that are capable of causing electronic excitation within molecules, which leads to changes in the bonding or chemistry of the molecule. At the lower end of the visible light spectrum, EMR becomes invisible to humans because its photons no longer have enough individual energy to cause a lasting molecular change in the visual molecule retinal in the human retina, which change triggers the sensation of vision.
There exist animals that are sensitive to various types of infrared, but not by means of quantum-absorption. Infrared sensing in snakes depends on a kind of natural thermal imaging, in which tiny packets of cellular water are raised in temperature by the infrared radiation. EMR in this range causes molecular vibration and heating effects, how these animals detect it. Above the range of visible light, ultraviolet light becomes invisible to humans because it is absorbed by the cornea below 360 nm and the internal lens below 400 nm. Furthermore, the rods and cones located in the retina of the human eye cannot detect the short ultraviolet wavelengths and are in fact damaged by ultraviolet. Many animals with eyes that do not require lenses are able to detect ultraviolet, by quantum photon-absorption mechanisms, in much the same chemical way that humans detect visible light. Various sources define visible light as narrowly as 420–680 nm to as broadly as 380–800 nm. Under ideal laboratory conditions, people can see infrared up to at least 1050 nm.
Plant growth is affected by the color spectrum of light, a process known as photomorphogenesis. The speed of light in a vacuum is defined to be 299,792,458 m/s; the fixed value of the speed of light in SI units results from the fact that the metre is now defined in terms of the speed of light. All forms of electromagnetic radiation move at this same speed in vacuum. Different physicists have attempted to measure the speed of light throughout history. Galileo attempted to measure the speed of light in the seventeenth century. An early experiment to measure the speed of light was conducted by Ole Rømer, a Danish physicist, in 1676. Using a telescope, Rømer observed one of its moons, Io. Noting discrepancies in the apparent period of Io's orbit, he calculated that light takes about 22 minutes to traverse the diameter of Earth's orbit. However, its size was not known at that time. If Rømer had known the diameter of the Earth's orbit, he would have calculated a speed of 227,000,000 m/s. Another, more accurate, measurement of the speed of light was performed in Europe by Hippolyte Fizeau in 1849.
Fizeau dire
Diving equipment
Diving equipment is equipment used by underwater divers to make diving activities possible, safer and/or more comfortable. This may be equipment intended for this purpose, or equipment intended for other purposes, found to be suitable for diving use; the fundamental item of diving equipment used by divers is underwater breathing apparatus, such as scuba equipment, surface supplied diving equipment, but there are other important pieces of equipment that make diving safer, more convenient or more efficient. Diving equipment used by recreational scuba divers is personal equipment carried by the diver, but professional divers when operating in the surface supplied or saturation mode, use a large amount of support equipment not carried by the diver. Equipment, used for underwater work or other activities, not directly related to the activity of diving, or which has not been designed or modified for underwater use by divers is excluded. Surface supplied diving - used in professional diving; this category includes: Surface oriented surface supplied diving, where the diver starts and finishes the dive at normal atmospheric pressure.
Saturation diving, where the diver remains under pressure in an underwater habitat or saturation spread between underwater excursions. Standard diving dress - used in professional diving. Of historical interest now. Airline or Hookah diving. "Compressor diving" - a rudimentary form of surface supplied diving used in the Philippines by artisanal fishermen. Recreational forms like snuba. Scuba diving - The use of self-contained underwater breathing apparatus; this category includes: Open-circuit scuba consisting of diving cylinder and diving regulator Rebreather, closed-circuit or semi-closed-circuit scuba Free diving or breathhold diving, where the diver completes the dive on a single breath of air taken at the surface before the dive. Snorkel allows breathing at the surface with the face submerged, is used as an adjunct to free diving and scuba. Atmospheric diving suits and other submersibles which isolate the diver from the ambient environment; these are not considered here. Liquid breathing systems are rare and at an early experimental stage.
It is hoped that some day practical systems will allow deep diving. This is not considered here; this is the diving equipment worn by or carried by the diver for personal protection or comfort, or to facilitate the diving aspect of the activity, may include a selection from: Scuba equipment: Primary cylinder, carried back-mounted or side mounted and open circuit regulator, or rebreather sets. Alternative air source such as bailout bottle or pony bottle, decompression cylinders and their associated regulators. Secondary demand valve. Surface supplied equipment: Helmet or full face mask, diver's umbilical, bailout block, bailout cylinder and regulator. Thermal and abrasion protection. In cold water, a diving suit such as a dry suit, a wet suit, or a Hot water suit is necessary. Boiler suit overalls are worn over the thermal protection suit by commercial divers as abrasion protection In warm water, many types of tough, everyday clothing provide protection, as well as purpose made garments such as dive skins and shorty wetsuits.
In some cases, simple regular swimsuits are used. Diving gloves, including wetsuit gloves and dry gloves and three-finger mitts Diving hoods Diving boots - With dry suits, the boots are integrated. Safety helmet for scuba diving. Diving chain mail may be used as protection against bites by large marine animals Diver's cages may be used as protection against large predators A backplate is a structure onto which the back-mounted diving cylinders are mounted linking the buoyancy compensator with the weight of the diving cylinders and provided with a harness of straps which secures the scuba set to the diver's back. A backplate is used with a back inflation type buoyancy compensator, but can be used without any buoyancy compensator. Buoyancy compensator known as Buoyancy Control Device, BCD or BC - is a back mounted or sleeveless jacket style device which includes an inflatable bladder used to adjust the buoyancy of the diver under water, provide positive buoyancy at the surface; the buoyancy compensator is an integral part of the harness system used to secure the scuba set to the diver.
The earlier collar style buoyancy compensator is used any more. Diver Propulsion Vehicle - to increase the range of the diver underwater Diving weighting system - to counteract the buoyancy of the diving suit and diver to allow descent. Professional divers may use additional weighting to ensure stability when working on the bottom Fins for efficient propulsion Depth gauge lets the diver monitor depth maximum depth and, when used with a watch and Decompression tables allows the diver to monitor decompression requirements; some digital depth gauges indicate ascent rate, an important factor in avoiding decompression sickness Pneumofathometer is the surface supplied diving depth gauge which displays the depth of the diver at the surface control panel. Dive computer helps the diver to avoid decompression sickness by indicating the decompression stops needed for the dive profile. Most dive computers indicate depth and ascent rate; some indicate oxygen toxicity exposure and water temperature, may provide other functions.
Dive timer is an instrument that records depth and elapsed time during the dive. It is possibl
