Fish are gill-bearing aquatic craniate animals that lack limbs with digits. They form a sister group to the tunicates. Included in this definition are the living hagfish and cartilaginous and bony fish as well as various extinct related groups. Tetrapods emerged within lobe-finned fishes, so cladistically they are fish as well. However, traditionally fish are rendered paraphyletic by excluding the tetrapods; because in this manner the term "fish" is defined negatively as a paraphyletic group, it is not considered a formal taxonomic grouping in systematic biology, unless it is used in the cladistic sense, including tetrapods. The traditional term pisces is considered a typological, but not a phylogenetic classification; the earliest organisms that can be classified as fish were soft-bodied chordates that first appeared during the Cambrian period. Although they lacked a true spine, they possessed notochords which allowed them to be more agile than their invertebrate counterparts. Fish would continue to evolve through the Paleozoic era.
Many fish of the Paleozoic developed external armor. The first fish with jaws appeared in the Silurian period, after which many became formidable marine predators rather than just the prey of arthropods. Most fish are ectothermic, allowing their body temperatures to vary as ambient temperatures change, though some of the large active swimmers like white shark and tuna can hold a higher core temperature. Fish can communicate in their underwater environments through the use of acoustic communication. Acoustic communication in fish involves the transmission of acoustic signals from one individual of a species to another; the production of sounds as a means of communication among fish is most used in the context of feeding, aggression or courtship behaviour. The sounds emitted by fish can vary depending on the stimulus involved, they can produce either stridulatory sounds by moving components of the skeletal system, or can produce non-stridulatory sounds by manipulating specialized organs such as the swimbladder.
Fish are abundant in most bodies of water. They can be found in nearly all aquatic environments, from high mountain streams to the abyssal and hadal depths of the deepest oceans, although no species has yet been documented in the deepest 25% of the ocean. With 33,600 described species, fish exhibit greater species diversity than any other group of vertebrates. Fish are an important resource for humans worldwide as food. Commercial and subsistence fishers hunt fish in wild fisheries or farm them in ponds or in cages in the ocean, they are caught by recreational fishers, kept as pets, raised by fishkeepers, exhibited in public aquaria. Fish have had a role in culture through the ages, serving as deities, religious symbols, as the subjects of art and movies. Fish do not represent a monophyletic group, therefore the "evolution of fish" is not studied as a single event. Early fish from the fossil record are represented by a group of small, armored fish known as ostracoderms. Jawless fish lineages are extinct.
An extant clade, the lampreys may approximate ancient pre-jawed fish. The first jaws are found in Placodermi fossils; the diversity of jawed vertebrates may indicate the evolutionary advantage of a jawed mouth. It is unclear if the advantage of a hinged jaw is greater biting force, improved respiration, or a combination of factors. Fish may have evolved from a creature similar to a coral-like sea squirt, whose larvae resemble primitive fish in important ways; the first ancestors of fish may have kept the larval form into adulthood, although the reverse is the case. Fish are a paraphyletic group: that is, any clade containing all fish contains the tetrapods, which are not fish. For this reason, groups such as the "Class Pisces" seen in older reference works are no longer used in formal classifications. Traditional classification divides fish into three extant classes, with extinct forms sometimes classified within the tree, sometimes as their own classes: Class Agnatha Subclass Cyclostomata Subclass Ostracodermi † Class Chondrichthyes Subclass Elasmobranchii Subclass Holocephali Class Placodermi † Class Acanthodii † Class Osteichthyes Subclass Actinopterygii Subclass Sarcopterygii The above scheme is the one most encountered in non-specialist and general works.
Many of the above groups are paraphyletic, in that they have given rise to successive groups: Agnathans are ancestral to Chondrichthyes, who again have given rise to Acanthodiians, the ancestors of Osteichthyes. With the arrival of phylogenetic nomenclature, the fishes has been split up into a more detailed scheme, with the following major groups: Class Myxini Class Pteraspidomorphi † Class Thelodonti † Class Anaspida † Class Petromyzontida or Hyperoartia Petromyzontidae Class Conodonta † Class Cephalaspidomorphi † Galeaspida † Pituriaspida † Osteostraci † Infraphylum Gnathostomata Class Placodermi † Class Chondrichthyes Class Acanthodii † Superclass Osteichthy
The common nightingale or nightingale known as rufous nightingale, is a small passerine bird best known for its powerful and beautiful song. It was classed as a member of the thrush family Turdidae, but is now more considered to be an Old World flycatcher, Muscicapidae, it belongs to a group of more terrestrial species called chats. "Nightingale" is derived from "night", the Old English galan, "to sing". The genus name Luscinia is Latin for "nightingale" and megarhynchos is from Ancient Greek megas, "great" and rhunkhos "bill"; the common nightingale is larger than the European robin, at 15–16.5 cm length. It is plain brown above except for the reddish tail, it is buff to white below. Sexes are similar; the eastern subspecies L. m. hafizi and L. m. africana have paler upperparts and a stronger face-pattern, including a pale supercilium. The song of the nightingale has been described as one of the most beautiful sounds in nature, inspiring songs, fairy tales, books, a great deal of poetry, it is a migratory insectivorous species breeding in forest and scrub in Europe and south-west Asia, wintering in sub-Saharan Africa.
It is not found in the Americas. The distribution is more southerly than the closely related thrush nightingale Luscinia luscinia, it nests near the ground in dense vegetation. Research in Germany found that favoured breeding habitat of nightingales was defined by a number of geographical factors. Less than 400 m above mean sea level mean air temperature during the growing season above 14 °C more than 20 days/year on which temperatures exceed 25 °C annual precipitation less than 750 millimetres aridity index lower than 0.35 no closed canopyIn the UK, the bird is at the northern limit of its range which has contracted in recent years, placing it on the red list for conservation. Despite local efforts to safeguard its favoured coppice and scrub habitat, numbers fell by 53 percent between 1995 and 2008. A survey conducted by the British Trust for Ornithology in 2012 and 2013 recorded some 3,300 territories, with most of these clustered in a few counties in the south-east of England, notably Kent, Essex and East and West Sussex.
By contrast, the European breeding population is estimated at between 3.2 and 7 million pairs, giving it green conservation status. Common nightingales are so named because they sing at night as well as during the day; the name has been used for more than 1,000 years, being recognisable in its Old English form nihtgale, which means "night songstress". Early writers assumed; the song is loud, with an impressive range of whistles and gurgles. Its song is noticeable at night because few other birds are singing; this is. Only unpaired males sing at night, nocturnal song serves to attract a mate. Singing at dawn, during the hour before sunrise, is assumed to be important in defending the bird's territory. Nightingales sing more loudly in urban or near-urban environments, in order to overcome the background noise; the most characteristic feature of the song is a loud whistling crescendo, absent from the song of thrush nightingale. It has a frog-like alarm call; the common nightingale is an important symbol for poets from a variety of ages, has taken on a number of symbolic connotations.
Homer evokes the nightingale in the Odyssey, suggesting the myth of Procne. This myth is the focus of Tereus, of which only fragments remain. Ovid, too, in his Metamorphoses, includes the most popular version of this myth and altered by poets, including Chrétien de Troyes, Geoffrey Chaucer, John Gower, George Gascoigne. T. S. Eliot's "The Waste Land" evokes the common nightingale's song; because of the violence associated with the myth, the nightingale's song was long interpreted as a lament. The common nightingale has been used as a symbol of poets or their poetry. Poets chose the nightingale as a symbol because of its creative and spontaneous song. Aristophanes's Birds and Callimachus both evoke the bird's song as a form of poetry. Virgil compares the mourning of Orpheus to the “lament of the nightingale”. In Sonnet 102 Shakespeare compares his love poetry to the song of the common nightingale: "Our love was new, but in the spring, When I was wont to greet it with my lays. For some romantic poets, the nightingale began to take on qualities of the muse.
The nightingale has a long history with symbolic associations ranging from "creativity, the muse, nature's purity, and, in Western spiritual tradition and goodness." Coleridge and Wordsworth saw the nightingale more as an instance of natural poetic creation: the nightingale became a voice of nature. John Keats' "Ode to a Nightingale" pictures the nightingale as an idealized poet who has achieved the poetry that Keats longs to write. Invoking a similar conception of the nightingale, Shelley wrote in his “A Defense of Poetry": "A poet is a nightingale who sits in darkness and sings to cheer its own solitude with sweet sounds.
Calibration in measurement technology and metrology is the comparison of measurement values delivered by a device under test with those of a calibration standard of known accuracy. Such a standard could be another measurement device of known accuracy, a device generating the quantity to be measured such as a voltage, sound tone, or a physical artefact, such as a metre ruler; the outcome of the comparison can result in no significant error being noted on the device under test, a significant error being noted but no adjustment made, or an adjustment made to correct the error to an acceptable level. Speaking, the term calibration means just the act of comparison, does not include any subsequent adjustment; the calibration standard is traceable to a national standard held by a National Metrological Institute. The formal definition of calibration by the International Bureau of Weights and Measures is the following: "Operation that, under specified conditions, in a first step, establishes a relation between the quantity values with measurement uncertainties provided by measurement standards and corresponding indications with associated measurement uncertainties and, in a second step, uses this information to establish a relation for obtaining a measurement result from an indication."This definition states that the calibration process is purely a comparison, but introduces the concept of measurement uncertainty in relating the accuracies of the device under test and the standard.
The increasing need for known accuracy and uncertainty and the need to have consistent and comparable standards internationally has led to the establishment of national laboratories. In many countries a National Metrology Institute will exist which will maintain primary standards of measurement which will be used to provide traceability to customer's instruments by calibration; the NMI supports the metrological infrastructure in that country by establishing an unbroken chain, from the top level of standards to an instrument used for measurement. Examples of National Metrology Institutes are NPL in the UK, NIST in the United States, PTB in Germany and many others. Since the Mutual Recognition Agreement was signed it is now straightforward to take traceability from any participating NMI and it is no longer necessary for a company to obtain traceability for measurements from the NMI of the country in which it is situated, such as the National Physical Laboratory in the UK. To improve the quality of the calibration and have the results accepted by outside organizations it is desirable for the calibration and subsequent measurements to be "traceable" to the internationally defined measurement units.
Establishing traceability is accomplished by a formal comparison to a standard, directly or indirectly related to national standards, international standards, or certified reference materials. This may be done by national standards laboratories operated by the government or by private firms offering metrology services. Quality management systems call for an effective metrology system which includes formal and documented calibration of all measuring instruments. ISO 9000 and ISO 17025 standards require that these traceable actions are to a high level and set out how they can be quantified. To communicate the quality of a calibration the calibration value is accompanied by a traceable uncertainty statement to a stated confidence level; this is evaluated through careful uncertainty analysis. Some times a DFS is required to operate machinery in a degraded state. Whenever this does happen, it must be in writing and authorized by a manager with the technical assistance of a calibration technician. Measuring devices and instruments are categorized according to the physical quantities they are designed to measure.
These vary internationally, e.g. NIST 150-2G in the U. S. and NABL-141 in India. Together, these standards cover instruments that measure various physical quantities such as electromagnetic radiation, sound and frequency, ionizing radiation, mechanical quantities, thermodynamic or thermal properties; the standard instrument for each test device varies accordingly, e.g. a dead weight tester for pressure gauge calibration and a dry block temperature tester for temperature gauge calibration. Calibration may be required for the following reasons: a new instrument after an instrument has been repaired or modified when a specified time period has elapsed when a specified usage has elapsed before and/or after a critical measurement after an event, for example after an instrument has been exposed to a shock, vibration, or physical damage, which might have compromised the integrity of its calibration sudden changes in weather whenever observations appear questionable or instrument indications do not match the output of surrogate instruments as specified by a requirement, e.g. customer specification, instrument manufacturer recommendation.
In general use, calibration is regarded as including the process of adjusting the output or indication on a measurement instrument to agree with value of the applied standard, within a specified accuracy. For example, a thermometer could be calibrated so the error of indication or the correction is determined, adjusted so that it shows the true temperature in Celsius at specific points on the scale; this is the perception of the instrument's end-user. However few instruments can be adjusted t
Biomass is plant or animal material used for energy production, heat production, or in various industrial processes as raw material for a range of products. It can be purposely grown energy crops, wood or forest residues, waste from food crops, food processing, animal farming, or human waste from sewage plants. Burning plant-derived biomass releases CO2, but it has still been classified as a renewable energy source in the EU and UN legal frameworks because photosynthesis cycles the CO2 back into new crops. In some cases, this recycling of CO2 from plants to atmosphere and back into plants can be CO2 negative, as a large portion of the CO2 is moved to the soil during each cycle. Cofiring with biomass has increased in coal power plants, because it makes it possible to release less CO2 without the cost assosicated with building new infrastructure. Co-firing is not without issues however an upgrade of the biomass is beneficiary. Upgrading to higher grade fuels can be achieved by different methods, broadly classified as thermal, chemical, or biochemical.
Humans have harnessed biomass-derived energy since the time when people began burning wood fuel. In 2019, biomass is the only source of fuel for domestic use in many developing countries. All biomass is biologically-produced matter based in carbon and oxygen; the estimated biomass production in the world is 100 billion metric tons of carbon per year, about half in the ocean and half on land. Wood and residues from wood, for instance spruce, eacalyptus, oil palm, remains the largest biomass energy source today, it is processed into pellet fuel or other forms of fuels. Biomass includes plant or animal matter that can be converted into fuel, fibers or industrial chemicals. There are numerous types of plants, including corn, miscanthus, sorghum and bamboo; the main waste energy feedstocks are wood waste, agricultural waste, municipal solid waste, manufacturing waste, landfill gas. Sewage sludge is another source of biomass. There is ongoing research involving algae-derived biomass. Other biomass feedstocks are enzymes or bacteria from various sources, grown in cell cultures or hydroponics.
Based on the source of biomass, biofuels are classified broadly into two major categories: First-generation biofuels are derived from food sources, such as sugarcane and corn starch. Sugars present in this biomass are fermented to produce bioethanol, an alcohol fuel which serve as an additive to gasoline, or in a fuel cell to produce electricity. Second-generation biofuels utilize non-food-based biomass sources such as perennial energy crops, agricultural/municipal waste. There is huge potential for second generation biofuels but the resources are under-utilized. Thermal conversion processes use heat as the dominant mechanism to upgrade biomass into a better and more practical fuel; the basic alternatives are torrefaction and gasification, these are separated principally by the extent to which the chemical reactions involved are allowed to proceed. There are other less common, more experimental or proprietary thermal processes that may offer benefits, such as hydrothermal upgrading; some have been developed for use on high moisture content biomass, including aqueous slurries, allow them to be converted into more convenient forms.
A range of chemical processes may be used to convert biomass into other forms, such as to produce a fuel, more practical to store and use, or to exploit some property of the process itself. Many of these processes are based in large part on similar coal-based processes, such as the Fischer-Tropsch synthesis. Biomass can be converted into multiple commodity chemicals; as biomass is a natural material, many efficient biochemical processes have developed in nature to break down the molecules of which biomass is composed, many of these biochemical conversion processes can be harnessed. In most cases, microorganisms are used to perform the conversion process: anaerobic digestion and composting. Glycoside hydrolases are the enzymes involved in the degradation of the major fraction of biomass, such as polysaccharides present in starch and lignocellulose. Thermostable variants are gaining increasing roles as catalysts in biorefining applications, since recalcitrant biomass needs thermal treatment for more efficient degradation.
Biomass can be directly converted to electrical energy via electrochemical oxidation of the material. This can be performed directly in a direct carbon fuel cell, direct liquid fuel cells such as direct ethanol fuel cell, a direct methanol fuel cell, a direct formic acid fuel cell, a L-ascorbic Acid Fuel Cell, a microbial fuel cell; the fuel can be consumed indirectly via a fuel cell system containing a reformer which converts the biomass into a mixture of CO and H2 before it is consumed in the fuel cell. On combustion, the carbon from biomass is released into the atmosphere as carbon dioxide. After a few months, or years, or decades, the CO2 has been absorbed back by growing trees. However, the carbon storage capacity of forests may be reduced overall if destructive forestry techniques are employed. All biomass crops sequester carbon. For example, soil organic carbon has been observed to be greater below switchgrass crops than under cultivated cropland at depths below 30 cm. For Miscanthus x giganteus, McCalmont et al. found accumulation rates ranging from 0.42 to 3.8 ton
The thrush nightingale known as the sprosser, is a small passerine bird, classed as a member of the thrush family Turdidae, but is now more considered to be an Old World flycatcher, Muscicapidae. It, similar small European species, are called chats, it is a migratory insectivorous species breeding in forests in Europe and Asia and overwintering in Africa. The distribution is more northerly than the closely related common nightingale, Luscinia megarhynchos, which it resembles in appearance, it nests near the ground in dense undergrowth. The thrush nightingale is similar in size to the European robin, it is plain greyish-brown white and greyish-brown below. Its greyer tones, giving a cloudy appearance to the underside, lack of the common nightingale's obvious rufous tail side patches are the clearest plumage differences from that species. Sexes are similar, it has a more powerful song than that of the nightingale. "Nightingale" is derived from "night", the Old English galan, "to sing". The genus name Luscinia is Latin for the common nightingale.
An adult thrush nightingale is about 16 centimetres long with a wingspan of 18 centimetres. The head and the whole of the upper parts of the thrush nightingale are dark brown with a slight olive tinge; the colour is not at all rufous. The upper tail-coverts are less olivaceous and the tail feathers are dark rufous-brown; the lores and ear-coverts are brownish-black and the chin and throat are pale buff or whitish, mottled with brown, are paler in colour than the nightingale. The sides of the throat are spotted brown and the pale feathers of the breast have brown central bands giving the breast a mottled appearance; the under tail-coverts are buff, sometimes marked with brown. The wing feathers and wing-coverts are dark brown and less rufous than the nightingale; the beak and feet are brown and the irises are dark brown. The sexes are similar to each other in appearance and the juveniles are darker and more mottled. There is a single moult in August at the end of the breeding season; the male's song is loud, with a range of whistles and clicks and includes a flute-like "pioo" with a pure bell-like tone.
It is sometimes interrupted by a rasping "dserr" sound and is rather solemn as compared to that of the nightingale. The song is quite distinctive, it is sometimes sung in the bird's winter quarters. The call-note "whit" is higher pitched and more abrupt; the thrush nightingale is a migrant species. It breeds in the western part of temperate Asia, its northern limit of its summer range extends to Denmark, southern Norway and Sweden, the Baltic States, the Republic of Karelia, Vologda, Kazakhstan and Altai. The southern limit extends from Austria and the Czech Republic, through Romania, southern Russia, the Crimea and northern Caucasus, it overwinters in Africa south of the Sahara. It is an occasional visitor to the British Isles. In its breeding range, the thrush nightingale is found in damp deciduous woodland with alder and birch, it favours thick undergrowth with brambles, dense shrubs and tangled vegetation in swampy places and near water. In its winter quarters it is found in dense patches of thorn bush in valley bottoms near water courses, sometimes in thick vegetation at the edge of woodland.
The thrush nightingale feeds chiefly on the ground taking earthworms and the adults and pupae of insects such as beetles, small moths and flies. In the autumn, the berries of currants and elders are eaten. Before crossing the Sahara on its migration, thrush nightingales build up their fat reserves, it has been found experimentally. A simulation of the magnetic field found in northern Egypt encouraged birds preparing to migrate from Sweden to further build up their body fat; the thrush nightingale breeds in damp forests, nesting on the ground in the middle of a bed of stinging nettles. The nest rests on a platform of dead leaves and is composed of dead grass stalks, bents and stems, lined with finer material, it is built by the female which lays five eggs. These are a milky-blue colour plain but sometimes with a slight speckling of rusty-brown and measure an average of 21.7 by 16.2 millimetres. The hen incubates the eggs; the young are fed by both parents and fledge when about eleven days old, but are not independent for another twelve days or so.
BirdLife International estimates that there are between eleven and twenty million thrush nightingales in Europe and that, as Europe forms somewhere between 50% and 74% of the bird's global range, the total world population may be between fifteen and forty one million individuals. In Europe the population seems to be slightly; the bird is considered to be of Least Concern by the International Union for Conservation of Nature IUCN. Avibase Thrush nightingale - Species text in The Atlas of Southern African Birds
The phonograph is a device for the mechanical recording and reproduction of sound. In its forms, it is called a gramophone or, since the 1940s, a record player; the sound vibration waveforms are recorded as corresponding physical deviations of a spiral groove engraved, incised, or impressed into the surface of a rotating cylinder or disc, called a "record". To recreate the sound, the surface is rotated while a playback stylus traces the groove and is therefore vibrated by it faintly reproducing the recorded sound. In early acoustic phonographs, the stylus vibrated a diaphragm which produced sound waves which were coupled to the open air through a flaring horn, or directly to the listener's ears through stethoscope-type earphones; the phonograph was invented in 1877 by Thomas Edison. While other inventors had produced devices that could record sounds, Edison's phonograph was the first to be able to reproduce the recorded sound, his phonograph recorded sound onto a tinfoil sheet wrapped around a rotating cylinder.
A stylus responding to sound vibrations produced an down or hill-and-dale groove in the foil. Alexander Graham Bell's Volta Laboratory made several improvements in the 1880s and introduced the graphophone, including the use of wax-coated cardboard cylinders and a cutting stylus that moved from side to side in a zigzag groove around the record. In the 1890s, Emile Berliner initiated the transition from phonograph cylinders to flat discs with a spiral groove running from the periphery to near the center, coining the term gramophone for disc record players, predominantly used in many languages. Improvements through the years included modifications to the turntable and its drive system, the stylus or needle, the sound and equalization systems; the disc phonograph record was the dominant audio recording format throughout most of the 20th century. In the 1980s, phonograph use on a standard record player declined due to the rise of the cassette tape, compact disc, other digital recording formats. However, records are still a favorite format for some audiophiles, DJs and turntablists, have undergone a revival in the 2010s.
The original recordings of musicians, which may have been recorded on tape or digital methods, are sometimes re-issued on vinyl. Usage of terminology is not uniform across the English-speaking world. In more modern usage, the playback device is called a "turntable", "record player", or "record changer"; when used in conjunction with a mixer as part of a DJ setup, turntables are colloquially called "decks". In electric phonographs, the motions of the stylus are converted into an analogous electrical signal by a transducer converted back into sound by a loudspeaker; the term phonograph was derived from the Greek words φωνή and γραφή. The similar related terms gramophone and graphophone have similar root meanings; the roots were familiar from existing 19th-century words such as photograph and telephone. The new term may have been influenced by the existing words phonographic and phonography, which referred to a system of phonetic shorthand. Arguably, any device used to record sound or reproduce recorded sound could be called a type of "phonograph", but in common practice the word has come to mean historic technologies of sound recording, involving audio-frequency modulations of a physical trace or groove.
In the late-19th and early-20th centuries, "Phonograph", "Gramophone", "Graphophone", "Zonophone", the like were still brand names specific to various makers of sometimes different machines. "Talking machine" had earlier been used to refer to complicated devices which produced a crude imitation of speech, by simulating the workings of the vocal cords and lips – a potential source of confusion both and now. In British English, "gramophone" may refer to any sound-reproducing machine using disc records, which were introduced and popularized in the UK by the Gramophone Company. "gramophone" was a proprietary trademark of that company and any use of the name by competing makers of disc records was vigorously prosecuted in the courts, but in 1910 an English court decision decreed that it had become a generic term. The term "phonograph" was restricted to machines that used cylinder records. "Gramophone" referred to a wind-up machine. After the introduction of the softer vinyl records, 33 1⁄3-rpm LPs and 45-rpm "single" or two-song records, EPs, the common name became "record player" or "turntable".
The home record player was part of a system that included a radio and might play audiotape cassettes. From about 1960, such a system began to be described as a "hi-fi" or a "stereo". In American English, "phonograph", properly specific to machines made by Edison, was sometimes used in a generic sense as early as the 1890s to include cylinder
Acoustics is the branch of physics that deals with the study of all mechanical waves in gases and solids including topics such as vibration, sound and infrasound. A scientist who works in the field of acoustics is an acoustician while someone working in the field of acoustics technology may be called an acoustical engineer; the application of acoustics is present in all aspects of modern society with the most obvious being the audio and noise control industries. Hearing is one of the most crucial means of survival in the animal world, speech is one of the most distinctive characteristics of human development and culture. Accordingly, the science of acoustics spreads across many facets of human society—music, architecture, industrial production and more. Animal species such as songbirds and frogs use sound and hearing as a key element of mating rituals or marking territories. Art, craft and technology have provoked one another to advance the whole, as in many other fields of knowledge. Robert Bruce Lindsay's'Wheel of Acoustics' is a well accepted overview of the various fields in acoustics.
The word "acoustic" is derived from the Greek word ἀκουστικός, meaning "of or for hearing, ready to hear" and that from ἀκουστός, "heard, audible", which in turn derives from the verb ἀκούω, "I hear". The Latin synonym is "sonic", after which the term sonics used to be a synonym for acoustics and a branch of acoustics. Frequencies above and below the audible range are called "ultrasonic" and "infrasonic", respectively. In the 6th century BC, the ancient Greek philosopher Pythagoras wanted to know why some combinations of musical sounds seemed more beautiful than others, he found answers in terms of numerical ratios representing the harmonic overtone series on a string, he is reputed to have observed that when the lengths of vibrating strings are expressible as ratios of integers, the tones produced will be harmonious, the smaller the integers the more harmonious the sounds. If, for example, a string of a certain length would sound harmonious with a string of twice the length. In modern parlance, if a string sounds the note C when plucked, a string twice as long will sound a C an octave lower.
In one system of musical tuning, the tones in between are given by 16:9 for D, 8:5 for E, 3:2 for F, 4:3 for G, 6:5 for A, 16:15 for B, in ascending order. Aristotle understood that sound consisted of compressions and rarefactions of air which "falls upon and strikes the air, next to it...", a good expression of the nature of wave motion. In about 20 BC, the Roman architect and engineer Vitruvius wrote a treatise on the acoustic properties of theaters including discussion of interference and reverberation—the beginnings of architectural acoustics. In Book V of his De architectura Vitruvius describes sound as a wave comparable to a water wave extended to three dimensions, when interrupted by obstructions, would flow back and break up following waves, he described the ascending seats in ancient theaters as designed to prevent this deterioration of sound and recommended bronze vessels of appropriate sizes be placed in theaters to resonate with the fourth, fifth and so on, up to the double octave, in order to resonate with the more desirable, harmonious notes.
During the Islamic golden age, Abū Rayhān al-Bīrūnī is believed to postulated that the speed of sound was much slower than the speed of light. The physical understanding of acoustical processes advanced during and after the Scientific Revolution. Galileo Galilei but Marin Mersenne, discovered the complete laws of vibrating strings. Galileo wrote "Waves are produced by the vibrations of a sonorous body, which spread through the air, bringing to the tympanum of the ear a stimulus which the mind interprets as sound", a remarkable statement that points to the beginnings of physiological and psychological acoustics. Experimental measurements of the speed of sound in air were carried out between 1630 and 1680 by a number of investigators, prominently Mersenne. Meanwhile, Newton derived the relationship for wave velocity in solids, a cornerstone of physical acoustics; the eighteenth century saw major advances in acoustics as mathematicians applied the new techniques of calculus to elaborate theories of sound wave propagation.
In the nineteenth century the major figures of mathematical acoustics were Helmholtz in Germany, who consolidated the field of physiological acoustics, Lord Rayleigh in England, who combined the previous knowledge with his own copious contributions to the field in his monumental work The Theory of Sound. In the 19th century, Wheatstone and Henry developed the analogy between electricity and acoustics; the twentieth century saw a burgeoning of technological applications of the large body of scientific knowledge, by in place. The first such application was Sabine’s groundbreaking work in architectural acoustics, many others followed. Underwater acoustics was used for detecting submarines in the first World War. Sound recording and the telephone played important roles in a global transformation of society. Sound measurement and analysis reached new levels of accuracy and sophistication through the use of electronics and computing; the ultrasonic frequency range enabled wholly new kinds of application in industry.
New kinds of transducers were put to use. Acoustics is defined by ANSI/