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Visual acuity

Visual acuity (VA) commonly refers to the clarity of vision, but technically rates an animal's ability to recognize small details with precision. Visual acuity depends on optical and neural factors. Optical factors of the eye influence the sharpness of an image on its retina. Neural factors include the health and functioning of the retina, of the neural pathways to the brain, and of the interpretative faculty of the brain.

The most commonly referred-to visual acuity is distance acuity or far acuity (e.g., "20/20 vision"), which describes someone's ability to recognize small details at a far distance. This ability is compromised in people with myopia, also known as short-sightedness or near-sightedness. Another visual acuity is near acuity, which describes someone's ability to recognize small details at a near distance. This ability is compromised in people with hyperopia, also known as long-sightedness or far-sightedness.

A common optical cause of low visual acuity is refractive error (ametropia): errors in how the light is refracted in the eye. Causes of refractive errors include aberrations in the shape of the eye or the cornea, and reduced ability of the lens to focus light. When the combined refractive power of the cornea and lens is too high for the length of the eye, the retinal image will be in focus in front of the retina and out of focus on the retina, yielding myopia. A similar poorly focused retinal image happens when the combined refractive power of the cornea and lens is too low for the length of the eye except that the focused image is behind the retina, yielding hyperopia. Normal refractive power is referred to as emmetropia. Other optical causes of low visual acuity include astigmatism, in which contours of a particular orientation are blurred, and more complex corneal irregularities.

Refractive errors can mostly be corrected by optical means (such as eyeglasses, contact lenses, and refractive surgery). For example, in the case of myopia, the correction is to reduce the power of the eye's refraction by a so-called minus lens.

Neural factors that limit acuity are located in the retina, in the pathways to the brain, or in the brain. Examples of conditions affecting the retina include detached retina and macular degeneration. Examples of conditions affecting the brain include amblyopia (caused by the visual brain not having developed properly in early childhood) and by brain damage, such as from traumatic brain injury or stroke. When optical factors are corrected for, acuity can be considered a measure of neural functioning.

Visual acuity is typically measured while fixating, i.e. as a measure of central (or foveal) vision, for the reason that it is highest in the very center. However, acuity in peripheral vision can be of equal importance in everyday life. Acuity declines towards the periphery first steeply and then more gradually, in an inverse-linear fashion (i.e. the decline follows approximately a hyperbola). The decline is according to E2/(E2+E), where E is eccentricity in degrees visual angle, and E2 is a constant of approximately 2 degrees. At 2 degrees eccentricity, for example, acuity is half the foveal value.

Visual acuity is a measure of how well small details are resolved in the very center of the visual field; it therefore does not indicate how larger patterns are recognized. Visual acuity alone thus cannot determine the overall quality of visual function.

Definition
Visual acuity is a measure of the spatial resolution of the visual processing system. VA, as it is sometimes referred to by optical professionals, is tested by requiring the person whose vision is being tested to identify so-called optotypes – stylized letters, Landolt rings, pediatric symbols, symbols for the illiterate, standardized Cyrillic letters in the Golovin–Sivtsev table, or other patterns – on a printed chart (or some other means) from a set viewing distance. Optotypes are represented as black symbols against a white background (i.e. at maximum contrast). The distance between the person's eyes and the testing chart is set so as to approximate "optical infinity" in the way the lens attempts to focus (far acuity), or at a defined reading distance (near acuity).

A reference value above which visual acuity is considered normal is called 6/6 vision, the USC equivalent of which is 20/20 vision: At 6 metres or 20 feet, a human eye with that performance is able to separate contours that are approximately 1.75 mm apart. Vision of 6/12 corresponds to lower performance, while vision of 6/3 to better performance. Normal individuals have an acuity of 6/4 or better (depending on age and other factors).

In the expression 6/x vision, the numerator (6) is the distance in metres between the subject and the chart and the denominator (x) the distance at which a person with 6/6 acuity would discern the same optotype. Thus, 6/12 means that a person with 6/6 vision would discern the same optotype from 12 metres away (i.e. at twice the distance). This is equivalent to saying that with 6/12 vision, the person possesses half the spatial resolution and needs twice the size to discern the optotype.

A simple and efficient way to state acuity is by converting the fraction to a decimal: 6/6 then corresponds to an acuity (or a Visus) of 1.0 (see Expression below), while 6/3 corresponds to 2.0, which is often attained by well-corrected healthy young subjects with binocular vision. Stating acuity as a decimal number is the standard in European countries, as required by the European norm (EN ISO 8596, previously DIN 58220).

The precise distance at which acuity is measured is not important as long as it is sufficiently far away and the size of the optotype on the retina is the same. That size is specified as a visual angle, which is the angle, at the eye, under which the optotype appears. For 6/6 = 1.0 acuity, the size of a letter on the Snellen chart or Landolt C chart is a visual angle of 5 arc minutes (1 arc min = 1/60 of a degree), which is a 43 point font at 20 feet. By the design of a typical optotype (like a Snellen E or a Landolt C), the critical gap that needs to be resolved is 1/5 this value, i.e., 1 arc min. The latter is the value used in the international definition of visual acuity:

Acuity is a measure of visual performance and does not relate to the eyeglass prescription required to correct vision. Instead, an eye exam seeks to find the prescription that will provide the best corrected visual performance achievable. The resulting acuity may be greater or less than 6/6 = 1.0. Indeed, a subject diagnosed as having 6/6 vision will often actually have higher visual acuity because, once this standard is attained, the subject is considered to have normal (in the sense of undisturbed) vision and smaller optotypes are not tested. Subjects with 6/6 vision or "better" (20/15, 20/10, etc.) may still benefit from an eyeglass correction for other problems related to the visual system, such as hyperopia, ocular injuries, or presbyopia.

Measurement
Visual acuity is measured by a psychophysical procedure and as such relates the physical characteristics of a stimulus to a subject's percept and their resulting responses. Measurement can be taken by using an eye chart invented by Ferdinand Monoyer, by optical instruments, or by computerized tests like the FrACT.

Care must be taken that viewing conditions correspond to the standard, such as correct illumination of the room and the eye chart, correct viewing distance, enough time for responding, error allowance, and so forth. In European countries, these conditions are standardized by the European norm (EN ISO 8596, previously DIN 58220).

Physiology
Daylight vision (i.e. photopic vision) is subserved by cone receptor cells which have high spatial density (in the central fovea) and allow high acuity of 6/6 or better. In low light (i.e., scotopic vision), cones do not have sufficient sensitivity and vision is subserved by rods. Spatial resolution is then much lower. This is due to spatial summation of rods, i.e. a number of rods merge into a bipolar cell, in turn connecting to a ganglion cell, and the resulting unit for resolution is large, and acuity small. There are no rods in the very center of the visual field (the foveola), and highest performance in low light is achieved in near peripheral vision.

The maximum angular resolution of the human eye is 28 arc seconds or 0.47 arc minutes; this gives an angular resolution of 0.008 degrees, and at a distance of 1 km corresponds to 136 mm. This is equal to 0.94 arc minutes per line pair (one white and one black line), or 0.016 degrees. For a pixel pair (one white and one black pixel) this gives a pixel density of 128 pixels per degree (PPD).

6/6 vision is defined as the ability to resolve two points of light separated by a visual angle of one minute of arc, corresponding to 60 PPD, or about 290–350 pixels per inch for a display on a device held 250 to 300 mm from the eye.

Thus, visual acuity, or resolving power (in daylight, central vision), is the property of cones. To resolve detail, the eye's optical system has to project a focused image on the fovea, a region inside the macula having the highest density of cone photoreceptor cells (the only kind of photoreceptors existing in the fovea's very center of 300 μm diameter), thus having the highest resolution and best color vision. Acuity and color vision, despite being mediated by the same cells, are different physiologic functions that do not interrelate except by position. Acuity and color vision can be affected independently.

The grain of a photographic mosaic has just as limited resolving power as the "grain" of the retinal mosaic. To see detail, two sets of receptors must be intervened by a middle set. The maximum resolution is that 30 seconds of arc, corresponding to the foveal cone diameter or the angle subtended at the nodal point of the eye. To get reception from each cone, as it would be if vision was on a mosaic basis, the "local sign" must be obtained from a single cone via a chain of one bipolar, ganglion, and lateral geniculate cell each. A key factor of obtaining detailed vision, however, is inhibition. This is mediated by neurons such as the amacrine and horizontal cells, which functionally render the spread or convergence of signals inactive. This tendency to one-to-one shuttle of signals is powered by brightening of the center and its surroundings, which triggers the inhibition leading to a one-to-one wiring. This scenario, however, is rare, as cones may connect to both midget and flat (diffuse) bipolars, and amacrine and horizontal cells can merge messages just as easily as inhibit them.

Light travels from the fixation object to the fovea through an imaginary path called the visual axis. The eye's tissues and structures that are in the visual axis (and also the tissues adjacent to it) affect the quality of the image. These structures are: tear film, cornea, anterior chamber, pupil, lens, vitreous, and finally the retina. The posterior part of the retina, called the retinal pigment epithelium (RPE) is responsible for, among many other things, absorbing light that crosses the retina so it cannot bounce to other parts of the retina. In many vertebrates, such as cats, where high visual acuity is not a priority, there is a reflecting tapetum layer that gives the photoreceptors a "second chance" to absorb the light, thus improving the ability to see in the dark. This is what causes an animal's eyes to seemingly glow in the dark when a light is shone on them. The RPE also has a vital function of recycling the chemicals used by the rods and cones in photon detection. If the RPE is damaged and does not clean up this "shed" blindness can result.

As in a photographic lens, visual acuity is affected by the size of the pupil. Optical aberrations of the eye that decrease visual acuity are at a maximum when the pupil is largest (about 8 mm), which occurs in low-light conditions. When the pupil is small (1–2 mm), image sharpness may be limited by diffraction of light by the pupil (see diffraction limit). Between these extremes is the pupil diameter that is generally best for visual acuity in normal, healthy eyes; this tends to be around 3 or 4 mm.

If the optics of the eye were otherwise perfect, theoretically, acuity would be limited by pupil diffraction, which would be a diffraction-limited acuity of 0.4 minutes of arc (minarc) or 6/2.6 acuity. The smallest cone cells in the fovea have sizes corresponding to 0.4 minarc of the visual field, which also places a lower limit on acuity. The optimal acuity of 0.4 minarc or 6/2.6 can be demonstrated using a laser interferometer that bypasses any defects in the eye's optics and projects a pattern of dark and light bands directly on the retina. Laser interferometers are now used routinely in patients with optical problems, such as cataracts, to assess the health of the retina before subjecting them to surgery.

The visual cortex is the part of the cerebral cortex in the posterior part of the brain responsible for processing visual stimuli, called the occipital lobe. The central 10° of field (approximately the extension of the macula) is represented by at least 60% of the visual cortex. Many of these neurons are believed to be involved directly in visual acuity processing.

Proper development of normal visual acuity depends on a human or an animal having normal visual input when it is very young. Any visual deprivation, that is, anything interfering with such input over a prolonged period of time, such as a cataract, severe eye turn or strabismus, anisometropia (unequal refractive error between the two eyes), or covering or patching the eye during medical treatment, will usually result in a severe and permanent decrease in visual acuity and pattern recognition in the affected eye if not treated early in life, a condition known as amblyopia. The decreased acuity is reflected in various abnormalities in cell properties in the visual cortex. These changes include a marked decrease in the number of cells connected to the affected eye as well as cells connected to both eyes in cortical area V1, resulting in a loss of stereopsis, i.e. depth perception by binocular vision (colloquially: "3D vision"). The period of time over which an animal is highly sensitive to such visual deprivation is referred to as the critical period.

The eye is connected to the visual cortex by the optic nerve coming out of the back of the eye. The two optic nerves come together behind the eyes at the optic chiasm, where about half of the fibers from each eye cross over to the opposite side and join fibers from the other eye representing the corresponding visual field, the combined nerve fibers from both eyes forming the optic tract. This ultimately forms the physiological basis of binocular vision. The tracts project to a relay station in the midbrain called the lateral geniculate nucleus, part of the thalamus, and then to the visual cortex along a collection of nerve fibers called the optic radiation.

Any pathological process in the visual system, even in older humans beyond the critical period, will often cause decreases in visual acuity. Thus measuring visual acuity is a simple test in accessing the health of the eyes, the visual brain, or pathway to the brain. Any relatively sudden decrease in visual acuity is always a cause for concern. Common causes of decreases in visual acuity are cataracts and scarred corneas, which affect the optical path, diseases that affect the retina, such as macular degeneration and diabetes, diseases affecting the optic pathway to the brain such as tumors and multiple sclerosis, and diseases affecting the visual cortex such as tumors and strokes.

Though the resolving power depends on the size and packing density of the photoreceptors, the neural system must interpret the receptors' information. As determined from single-cell experiments on the cat and primate, different ganglion cells in the retina are tuned to different spatial frequencies, so some ganglion cells at each location have better acuity than others. Ultimately, however, it appears that the size of a patch of cortical tissue in visual area V1 that processes a given location in the visual field (a concept known as cortical magnification) is equally important in determining visual acuity. In particular, that size is largest in the fovea's center, and decreases with increasing distance from there.

Optical aspects
Besides the neural connections of the receptors, the optical system is an equally key player in retinal resolution. In the ideal eye, the image of a diffraction grating can subtend 0.5 micrometre on the retina. This is certainly not the case, however, and furthermore the pupil can cause diffraction of the light. Thus, black lines on a grating will be mixed with the intervening white lines to make a gray appearance. Defective optical issues (such as uncorrected myopia) can render it worse, but suitable lenses can help. Images (such as gratings) can be sharpened by lateral inhibition, i.e., more highly excited cells inhibiting the less excited cells. A similar reaction is in the case of chromatic aberrations, in which the color fringes around black-and-white objects are inhibited similarly.

Expression
Visual acuity is often measured according to the size of letters viewed on a Snellen chart or the size of other symbols, such as Landolt Cs or the E Chart.

In some countries, acuity is expressed as a vulgar fraction, and in some as a decimal number. Using the metre as a unit of measurement, (fractional) visual acuity is expressed relative to 6/6. Otherwise, using the foot, visual acuity is expressed relative to 20/20. For all practical purposes, 20/20 vision is equivalent to 6/6. In the decimal system, acuity is defined as the reciprocal value of the size of the gap (measured in arc minutes) of the smallest Landolt C, the orientation of which can be reliably identified. A value of 1.0 is equal to 6/6.

LogMAR is another commonly used scale, expressed as the (decadic) logarithm of the minimum angle of resolution (MAR), which is the reciprocal of the acuity number. The LogMAR scale converts the geometric sequence of a traditional chart to a linear scale. It measures visual acuity loss: positive values indicate vision loss, while negative values denote normal or better visual acuity. This scale is commonly used clinically and in research because the lines are of equal length and so it forms a continuous scale with equally spaced intervals between points, unlike Snellen charts, which have different numbers of letters on each line.

A visual acuity of 6/6 is frequently described as meaning that a person can see detail from 6 m away the same as a person with "normal" eyesight would see from 6 metres. If a person has a visual acuity of 6/12, they are said to see detail from 6 m away the same as a person with "normal" eyesight would see it from 12 m away.

The definition of 6/6 is somewhat arbitrary, since human eyes typically have higher acuity, as Tscherning writes, "We have found also that the best eyes have a visual acuity which approaches 2, and we can be almost certain that if, with a good illumination, the acuity is only equal to 1, the eye presents defects sufficiently pronounced to be easily established." Most observers may have a binocular acuity superior to 6/6; the limit of acuity in the unaided human eye is around 6/3–6/2.4 (20/10–20/8), although 6/3 was the highest score recorded in a study of some US professional athletes. Some birds of prey, such as hawks, are believed to have an acuity of around 20/2; in this respect, their vision is much better than human eyesight.

When visual acuity is below the largest optotype on the chart, the reading distance is reduced until the patient can read it. Once the patient is able to read the chart, the letter size and test distance are noted. If the patient is unable to read the chart at any distance, they are tested as follows:

Legal definitions
Various countries have defined statutory limits for poor visual acuity that qualifies as a disability. For example, in Australia, the Social Security Act defines blindness as:

"A person meets the criteria for permanent blindness under section 95 of the Social Security Act if the corrected visual acuity is less than 6/60 on the Snellen Scale in both eyes or there is a combination of visual defects resulting in the same degree of permanent visual loss."

In the US, the relevant federal statute defines blindness as follows:

"[T]he term 'blindness' means central visual acuity of 20/200 or less in the better eye with the use of a correcting lens. An eye that is accompanied by a limitation in the fields of vision such that the widest diameter of the visual field subtends an angle no greater than 20 degrees shall be considered for purposes in this paragraph as having a central visual acuity of 20/200 or less."

A person's visual acuity is registered documenting the following: whether the test was for distant or near vision, the eye(s) evaluated and whether corrective lenses (i.e. glasses or contact lenses) were used: So, distant visual acuity of 6/10 and 6/8 with pinhole in the right eye will be: DscOD 6/10 PH 6/8. Distant visual acuity of count fingers and 6/17 with pinhole in the left eye will be: DscOS CF PH 6/17. Near visual acuity of 6/8 with pinhole remaining at 6/8 in both eyes with spectacles will be: NccOU 6/8 PH 6/8.
 * Distance from the chart
 * D (distant) for the evaluation done at 20 ft.
 * N (near) for the evaluation done at 15.7 in.
 * Eye evaluated
 * OD (Latin oculus dexter) for the right eye.
 * OS (Latin oculus sinister) for the left eye.
 * OU (Latin oculi uterque) for both eyes.
 * Usage of spectacles during the test
 * cc (Latin cum correctore) with correctors.
 * sc: (Latin sine correctore) without correctors.
 * Pinhole occluder
 * The abbreviation PH is followed by the visual acuity as measured with a pinhole occluder, which temporarily corrects for refractive errors such as myopia or astigmatism.
 * PHNI means no improvement of visual acuity using a pinhole occluder.

"Dynamic visual acuity" defines the ability of the eye to visually discern fine detail in a moving object.

Measurement considerations
Visual acuity measurement involves more than being able to see the optotypes. The patient should be cooperative, understand the optotypes, be able to communicate with the physician, and many more factors. If any of these factors is missing, then the measurement will not represent the patient's real visual acuity.

Visual acuity is a subjective test meaning that if the patient is unwilling or unable to cooperate, the test cannot be done. A patient who is sleepy, intoxicated, or has any disease that can alter their consciousness or mental status, may not achieve their maximum possible acuity.

Patients who are illiterate in the language whose letters and/or numbers appear on the chart will be registered as having very low visual acuity if this is not known. Some patients will not tell the examiner that they do not know the optotypes, unless asked directly about it. Brain damage can result in a patient not being able to recognize printed letters, or being unable to spell them.

A motor inability can make a person respond incorrectly to the optotype shown and negatively affect the visual acuity measurement.

Variables such as pupil size, background adaptation luminance, duration of presentation, type of optotype used, interaction effects from adjacent visual contours (or "crowding") can all affect visual acuity measurement.

Testing in children
The newborn's visual acuity is approximately 6/133, developing to 6/6 well after the age of six months in most children, according to a study published in 2009.

The measurement of visual acuity in infants, pre-verbal children and special populations (for instance, disabled individuals) is not always possible with a letter chart. For these populations, specialised testing is necessary. As a basic examination step, one must check whether visual stimuli can be fixated, centered and followed.

More formal testing using preferential looking techniques use Teller acuity cards (presented by a technician from behind a window in the wall) to check whether the child is more visually attentive to a random presentation of vertical or horizontal gratings on one side compared with a blank page on the other side – the bars become progressively finer or closer together, and the endpoint is noted when the child in its adult carer's lap equally prefers the two sides.

Another popular technique is electro-physiologic testing using visual evoked (cortical) potentials (VEPs or VECPs), which can be used to estimate visual acuity in doubtful cases and expected severe vision loss cases like Leber's congenital amaurosis.

VEP testing of acuity is somewhat similar to preferential looking in using a series of black and white stripes (sine wave gratings) or checkerboard patterns (which produce larger responses than stripes). Behavioral responses are not required and brain waves created by the presentation of the patterns are recorded instead. The patterns become finer and finer until the evoked brain wave just disappears, which is considered to be the endpoint measure of visual acuity. In adults and older, verbal children capable of paying attention and following instructions, the endpoint provided by the VEP corresponds very well to the psychophysical measure in the standard measurement (i.e. the perceptual endpoint determined by asking the subject when they can no longer see the pattern). There is an assumption that this correspondence also applies to much younger children and infants, though this does not necessarily have to be the case. Studies do show the evoked brain waves, as well as derived acuities, are very adult-like by one year of age.

For reasons not totally understood, until a child is several years old, visual acuities from behavioral preferential looking techniques typically lag behind those determined using the VEP, a direct physiological measure of early visual processing in the brain. Possibly it takes longer for more complex behavioral and attentional responses, involving brain areas not directly involved in processing vision, to mature. Thus the visual brain may detect the presence of a finer pattern (reflected in the evoked brain wave), but the "behavioral brain" of a small child may not find it salient enough to pay special attention to.

A simple but less-used technique is checking oculomotor responses with an optokinetic nystagmus drum, where the subject is placed inside the drum and surrounded by rotating black and white stripes. This creates involuntary abrupt eye movements (nystagmus) as the brain attempts to track the moving stripes. There is a good correspondence between the optokinetic and usual eye-chart acuities in adults. A potentially serious problem with this technique is that the process is reflexive and mediated in the low-level brain stem, not in the visual cortex. Thus someone can have a normal optokinetic response and yet be cortically blind with no conscious visual sensation.

"Normal" visual acuity
Visual acuity depends upon how accurately light is focused on the retina, the integrity of the eye's neural elements, and the interpretative faculty of the brain. "Normal" visual acuity (in central, i.e. foveal vision) is frequently considered to be what was defined by Herman Snellen as the ability to recognize an optotype when it subtended 5 minutes of arc, that is Snellen's chart 6/6-metre, 20/20 feet, 1.00 decimal or 0.0 logMAR. In young humans, the average visual acuity of a healthy, emmetropic eye (or ametropic eye with correction) is approximately 6/5 to 6/4, so it is inaccurate to refer to 6/6 visual acuity as "perfect" vision. On the contrary, Tscherning writes, "We have found also that the best eyes have a visual acuity which approaches 2, and we can be almost certain that if, with a good illumination, the acuity is only equal to 1, the eye presents defects sufficiently pronounced to be easily established."

6/6 is the visual acuity needed to discriminate two contours separated by 1 arc minute – 1.75 mm at 6 metres. This is because a 6/6 letter, E for example, has three limbs and two spaces in between them, giving 5 different detailed areas. The ability to resolve this therefore requires 1/5 of the letter's total size, which in this case would be 1 minute of arc (visual angle). The significance of the 6/6 standard can best be thought of as the lower limit of normal, or as a screening cutoff. When used as a screening test, subjects that reach this level need no further investigation, even though the average visual acuity with a healthy visual system is typically better.

Some people may have other visual problems, such as severe visual field defects, color blindness, reduced contrast, mild amblyopia, cerebral visual impairments, inability to track fast-moving objects, or one of many other visual impairments and still have "normal" visual acuity. Thus, "normal" visual acuity does not imply normal vision. The reason visual acuity is very widely used is that it is easily measured, its reduction (after correction) often indicates some disturbance, and that it often corresponds with the normal daily activities a person can handle, and evaluates their impairment to do them (even though there is heavy debate over that relationship).

Other measures
Normally, visual acuity refers to the ability to resolve two separated points or lines, but there are other measures of the ability of the visual system to discern spatial differences.

Vernier acuity measures the ability to align two line segments. Humans can do this with remarkable accuracy. This success is regarded as hyperacuity. Under optimal conditions of good illumination, high contrast, and long line segments, the limit to vernier acuity is about 8 arc seconds or 0.13 arc minutes, compared to about 0.6 arc minutes (6/4) for normal visual acuity or the 0.4 arc minute diameter of a foveal cone. Because the limit of vernier acuity is well below that imposed on regular visual acuity by the "retinal grain" or size of the foveal cones, it is thought to be a process of the visual cortex rather than the retina. Supporting this idea, vernier acuity seems to correspond very closely (and may have the same underlying mechanism) enabling one to discern very slight differences in the orientations of two lines, where orientation is known to be processed in the visual cortex.

The smallest detectable visual angle produced by a single fine dark line against a uniformly illuminated background is also much less than foveal cone size or regular visual acuity. In this case, under optimal conditions, the limit is about 0.5 arc seconds or only about 2% of the diameter of a foveal cone. This produces a contrast of about 1% with the illumination of surrounding cones. The mechanism of detection is the ability to detect such small differences in contrast or illumination, and does not depend on the angular width of the bar, which cannot be discerned. Thus as the line gets finer, it appears to get fainter but not thinner.

Stereoscopic acuity is the ability to detect differences in depth with the two eyes. For more complex targets, stereoacuity is similar to normal monocular visual acuity, or around 0.6–1.0 arc minutes, but for much simpler targets, such as vertical rods, may be as low as only 2 arc seconds. Although stereoacuity normally corresponds very well with monocular acuity, it may be very poor, or absent, even in subjects with normal monocular acuities. Such individuals typically have abnormal visual development when they are very young, such as an alternating strabismus, or eye turn, where both eyes rarely, or never, point in the same direction and therefore do not function together.

Another test, including Visual acuity (EVTS/OptimEyes), uses targets which change in size, contrast, and viewing time. This test was developed by Daniel M. Laby with colleagues and uses item response theory to calculate a vision performance score (core score). This specific test of visual function has been shown to correlate to professional sports performance.

Motion acuity
The eye has acuity limits for detecting motion. Forward motion is limited by the subtended angular velocity detection threshold (SAVT), and horizontal and vertical motion acuity are limited by lateral motion thresholds. The lateral motion limit is generally below the looming motion limit, and for an object of a given size, lateral motion becomes the more insightful of the two, once the observer moves sufficiently far away from the path of travel. Below these thresholds subjective constancy is experienced in accordance with the Stevens' power law and Weber–Fechner law.

Subtended angular velocity detection threshold (SAVT)
There is a specific acuity limit in detecting an approaching object's looming motion. This is regarded as the subtended angular velocity detection threshold (SAVT) limit of visual acuity. It has a practical value of 0.0275 rad/s. For a person with SAVT limit of $$\dot\theta_t$$, the looming motion of a directly approaching object of size $acuity = 1⁄gap size [arc min].$, moving at velocity $S$, is not detectable until its distance $v$ is

 * $$D \lessapprox \sqrt{\frac{S \cdot v}{\dot{\theta_{t}}}-\frac{S^2}{4}},$$

where the $D$ term is omitted for small objects relative to great distances by small-angle approximation.

To exceed the SAVT, an object of size $S^{2}/4$ moving as velocity $S$ must be closer than $v$; beyond that distance, subjective constancy is experienced. The SAVT $$\dot\theta_t$$ can be measured from the distance at which a looming object is first detected:

 * $$ \dot\theta_t \approx \frac{4S \cdot v}{S^2 + 4D^2}, $$

where the $D$ term is omitted for small objects relative to great distances by small-angle approximation.

The SAVT has the same kind of importance to driving safety and sports as the static limit. The formula is derived from taking the derivative of the visual angle with respect to distance, and then multiplying by velocity to obtain the time rate of visual expansion ($S^{2}$).

Lateral motion
There are acuity limits ($$\dot\theta_t$$) of horizontal and vertical motion as well. They can be measured and defined by the threshold detection of movement of an object traveling at distance $d θ /d t = d θ /d x · d x /d t$ and velocity $D$ orthogonal to the direction of view, from a set-back distance $v$ with the formula
 * $$ \dot\theta_t \approx \frac{B \cdot v}{B^2 + D^2}. $$

Because the tangent of the subtended angle is the ratio of the orthogonal distance to the set-back distance, the angular time rate (rad/s) of lateral motion is simply the derivative of the inverse tangent multiplied by the velocity ($B$). In application this means that an orthogonally traveling object will not be discernible as moving until it has reached the distance

 * $$ D \lessapprox \sqrt{\frac{B \cdot v}{\dot\theta_t} - B^2}, $$

where $$\dot\theta_t$$ for lateral motion is generally ≥ 0.0087 rad/s with probable dependence on deviation from the fovia and movement orientation, velocity is in terms of the distance units, and zero distance is straight ahead. Far object distances, close set-backs, and low velocities generally lower the salience of lateral motion. Detection with close or null set-back can be accomplished through the pure scale changes of looming motion.

Radial motion
The motion acuity limit affects radial motion in accordance to its definition, hence the ratio of the velocity $d θ /d t = d θ /d x · d x /d t$ to the radius $v$ must exceed $$\dot\theta_t$$:
 * $$\dot\theta_t \lessapprox \frac{v}{R}.$$

Radial motion is encountered in clinical and research environments, in dome theaters, and in virtual-reality headsets.

title: Visual acuity


text:
Hartshorn

Hartshorn is the antler of male red deer.

Derivatives
Various nitrogen compounds were made from hartshorn shavings:
 * Oil of hartshorn is a crude chemical product obtained from the destructive distillation of deer antlers.
 * Salt of hartshorn refers to ammonium carbonate, an early form of smelling salts obtained by dry distillation of oil of hartshorn.
 * Spirit of hartshorn (or spirits of hartshorn) is an archaic name for aqueous ammonia. Originally, this term was applied to a solution manufactured from the hooves and antlers of the red deer, as well as those of some other animals. The aqueous solution was colorless and pungent, consisting of about 28.5 percent ammonia. It was used chiefly as a detergent, for removing stains and extracting certain vegetable coloring agents, and in the manufacture of ammonium salts. Later, the term was applied to the partially purified similar products of the action of heat on nitrogenous animal matter generally. Finally, the term was applied to any aqueous solution of ammonia.

Medicine
Hartshorn jelly or a decoction of burnt hartshorn in water was used to treat diarrhea. The coal of hartshorn, called calcinated hartshorn, was used as an absorbent, as well as in the treatment of dysentery. Salt of hartshorn (ammonium carbonate) was used as a sudorific for treatment of fevers, and as a smelling salt. Hartshorn was used to treat insect bites, sunstroke, stye, and snakebites.

Baking
Hartshorn salt (ammonium carbonate), also known simply as hartshorn, and baker's ammonia, was used as a leavening agent, in the baking of cookies and other edible treats. It was used mainly in the seventeenth and eighteenth centuries as a forerunner of baking powder. A half-teaspoon of hartshorn can substitute for one teaspoon of baking powder. It is called for in old German and Scandinavian recipes and, although rarely used in modern times, may still be purchased as a baking ingredient. Hartshorn helps molded cookies such as Springerle to retain their intricate designs during baking. Cookies made with hartshorn can be kept for a long time without hardening. Use of hartshorn may turn some ingredients, such as sunflower seeds, green.

Ammonium carbonate is especially suited to thin, dry cookies and crackers. When heated, it releases ammonia and carbon dioxide gases, but no water. The absence of water allows cookies to cook and dry out more quickly, and thinner cookies allow the pungent ammonia to escape, rather than to remain trapped, as it would in a deeper mass.

Safety concerns
Ammonia released during the baking process reacts with glucose and fructose to form intermediate molecules that in turn, react with asparagine (an amino acid found in nuts, seeds, and whole grains) to form acrylamide, a carcinogen.

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title: Hartshorn


text:
History of Somerset

Somerset is a historic county in the south west of England. There is evidence of human occupation since prehistoric times with hand axes and flint points from the Palaeolithic and Mesolithic eras, and a range of burial mounds, hill forts and other artefacts dating from the Neolithic, Bronze and Iron Ages. The oldest dated human road work in Great Britain is the Sweet Track, constructed across the Somerset Levels with wooden planks in the 39th century BCE.

Following the Roman Empire's invasion of southern Britain, the mining of lead and silver in the Mendip Hills provided a basis for local industry and commerce. Bath became the site of a major Roman fort and city, the remains of which can still be seen. During the Early Medieval period Somerset was the scene of battles between the Anglo-Saxons and first the Britons and later the Danes. In this period it was ruled first by various kings of Wessex, and later by kings of England. Following the defeat of the Anglo-Saxon monarchy by the Normans in 1066, castles were built in Somerset.

Expansion of the population and settlements in the county continued during the Tudor and more recent periods. Agriculture and coal mining expanded until the 18th century, although other industries declined during the industrial revolution. In modern times the population has grown, particularly in the seaside towns, notably Weston-super-Mare. Agriculture continues to be a major business, if no longer a major employer because of mechanisation. Light industries are based in towns such as Bridgwater and Yeovil. The towns of Taunton and Shepton Mallet manufacture cider, although the acreage of apple orchards is less than it once was.

Palaeolithic and Mesolithic
The Palaeolithic and Mesolithic periods saw hunter-gatherers move into the region of Somerset. There is evidence from flint artefacts in a quarry at Westbury that an ancestor of modern man, possibly Homo heidelbergensis, was present in the area from around 500,000 years ago. There is still some doubt about whether the artefacts are of human origin but they have been dated within Oxygen Isotope Stage 13 (524,000 – 478,000 BP). Other experts suggest that "many of the bone-rich Middle Pleistocene deposits belong to a single but climatically variable interglacial that succeeded the Cromerian, perhaps about 500,000 years ago. Detailed analysis of the origin and modification of the flint artefacts leads to the conclusion that the assemblage was probably a product of geomorphological processes rather than human work, but a single cut-marked bone suggests a human presence." Animal bones and artefacts unearthed in the 1980s at Westbury-sub-Mendip, in Somerset, have shown evidence of early human activity approximately 700,000 years ago.

Homo sapiens sapiens, or modern man, came to Somerset during the Early Upper Palaeolithic. There is evidence of occupation of four Mendip caves 35,000 to 30,000 years ago. During the Last Glacial Maximum, about 25,000 to 15,000 years ago, it is probable that Somerset was deserted as the area experienced tundra conditions. Evidence was found in Gough's Cave of deposits of human bone dating from around 12,500 years ago. The bones were defleshed and probably ritually buried though perhaps related to cannibalism being practised in the area at the time or making skull cups or storage containers. Somerset was one of the first areas of future England settled following the end of Younger Dryas phase of the last ice age c. 8000 BC. Cheddar Man is the name given to the remains of a human male found in Gough's Cave in Cheddar Gorge. He is Britain's oldest complete human skeleton. The remains date from about 7150 BC, and it appears that he died a violent death. Somerset is thought to have been occupied by Mesolithic hunter-gatherers from about 6000 BCE; Mesolithic artefacts have been found in more than 70 locations. Mendip caves were used as burial places, with between 50 and 100 skeletons being found in Aveline's Hole. In the Neolithic era, from about 3500 BCE, there is evidence of farming.

At the end of the last ice age the Bristol Channel was dry land, but later the sea level rose, particularly between 1220 and 900 BC and between 800 and 470 BCE, resulting in major coastal changes. The Somerset Levels became flooded, but the dry points such as Glastonbury and Brent Knoll have a long history of settlement, and are known to have been occupied by Mesolithic hunters. The county has prehistoric burial mounds (such as Stoney Littleton Long Barrow), stone rows (such as the circles at Stanton Drew and Priddy) and settlement sites. Evidence of Mesolithic occupation has come both from the upland areas, such as in Mendip caves, and from the low land areas such as the Somerset Levels. Dry points in the latter such as Glastonbury Tor and Brent Knoll, have a long history of settlement with wooden trackways between them. There were also "lake villages" in the marsh such as those at Glastonbury Lake Village and Meare. One of the oldest dated human road work in Britain is the Sweet Track, constructed across the Somerset Levels with wooden planks in the 39th century BC,   partially on the route of the even earlier Post Track.

Neolithic, Bronze and Iron Ages

There is evidence of Exmoor's human occupation from Mesolithic times onwards. In the Neolithic period people started to manage animals and grow crops on farms cleared from the woodland, rather than act purely as hunter gatherers. It is also likely that extraction and smelting of mineral ores to make tools, weapons, containers and ornaments in bronze and then iron started in the late Neolithic and into the Bronze and Iron Ages.

The caves of the Mendip Hills were settled during the Neolithic period and contain extensive archaeological sites such as those at Cheddar Gorge. There are numerous Iron Age Hill Forts, which were later reused in the Dark Ages, such as Cadbury Castle, Worlebury Camp and Ham Hill. The age of the henge monument at Stanton Drew stone circles is unknown, but is believed to be from the Neolithic period. There is evidence of mining on the Mendip Hills back into the late Bronze Age when there were technological changes in metal working indicated by the use of lead. There are numerous "hill forts", such as Small Down Knoll, Solsbury Hill, Dolebury Warren and Burledge Hill, which seem to have had domestic purposes, not just a defensive role. They generally seem to have been occupied intermittently from the Bronze Age onward, some, such as Cadbury Camp at South Cadbury, being refurbished during different eras. Battlegore Burial Chamber is a Bronze Age burial chamber at Williton which is composed of three round barrows and possibly a long, chambered barrow.

The Iron Age tribes of later Somerset were the Dobunni in north Somerset, Durotriges in south Somerset and Dumnonii in west Somerset. The first and second produced coins, the finds of which allows their tribal areas to be suggested, but the latter did not. All three had a Celtic culture and language. However, Ptolemy stated that Bath was in the territory of the Belgae, but this may be a mistake. The Celtic gods were worshipped at the temple of Sulis at Bath and possibly the temple on Brean Down. Iron Age sites on the Quantock Hills, include major hill forts at Dowsborough and Ruborough, as well as smaller earthwork enclosures, such as Trendle Ring, Elworthy Barrows and Plainsfield Camp.

Roman
Somerset was part of the Roman Empire from 47 AD to about 409 AD. However, the end was not abrupt and elements of Romanitas lingered on for perhaps a century.

Somerset was invaded from the south-east by the Second Legion Augusta, under the future emperor Vespasian. The hillforts of the Durotriges at Ham Hill and Cadbury Castle were captured. Ham Hill probably had a temporary Roman occupation. The massacre at Cadbury Castle seems to have been associated with the later Boudiccan Revolt of 60–61 AD. The county remained part of the Roman Empire until around 409 AD.

The Roman invasion, and possibly the preceding period of involvement in the internal affairs of the south of England, was inspired in part by the potential of the Mendip Hills. A great deal of the attraction of the lead mines may have been the potential for the extraction of silver.

Forts were set up at Bath and Ilchester. The lead and silver mines at Charterhouse in the Mendip Hills were run by the military. The Romans established a defensive boundary along the new military road known the Fosse Way (from the Latin fossa meaning ditch). The Fosse Way ran through Bath, Shepton Mallet, Ilchester and south-west towards Axminster. The road from Dorchester ran through Yeovil to meet the Fosse Way at Ilchester. Small towns and trading ports were set up, such as Camerton and Combwich. The larger towns decayed in the latter part of the period, though the smaller ones appear to have decayed less. In the latter part of the period, Ilchester seems to have been a "civitas" capital and Bath may also have been one. Particularly to the east of the River Parrett, villas were constructed. However, only a few Roman sites have been found to the west of the river. The villas have produced important mosaics and artifacts. Cemeteries have been found outside the Roman towns of Somerset and by Roman temples such as that at Lamyatt. Romano-British farming settlements, such as those at Catsgore and Sigwells, have been found in Somerset. There was salt production on the Somerset Levels near Highbridge and quarrying took place near Bath, where the Roman Baths gave their name to Bath.

Excavations carried out before the flooding of Chew Valley Lake also uncovered Roman remains, indicating agricultural and industrial activity from the second half of the 1st century until the 3rd century AD. The finds included a moderately large villa at Chew Park, where wooden writing tablets (the first in the UK) with ink writing were found. There is also evidence from the Pagans Hill Roman Temple at Chew Stoke. In October 2001 the West Bagborough Hoard of 4th century Roman silver was discovered in West Bagborough. The 681 coins included two denarii from the early 2nd century and 8 Miliarense and 671 Siliqua all dating to the period AD 337 – 367. The majority were struck in the reigns of emperors Constantius II and Julian and derive from a range of mints including Arles and Lyons in France, Trier in Germany and Rome.

In April 2010, the Frome Hoard, one of the largest-ever hoards of Roman coins discovered in Britain, was found by a metal detectorist. The hoard of 52,500 coins dated from the 3rd century AD and was found buried in a field near Frome, in a jar 14 in below the surface. The coins were excavated by archaeologists from the Portable Antiquities Scheme.

Sub-Roman period
This is the period from about 409 AD to the start of Saxon political control, which was mainly in the late 7th century, though they are said to have captured the Bath area in 577 AD. Initially the Britons of Somerset seem to have continued much as under the Romans but without the imperial taxation and markets. There was then a period of civil war in Britain though it is not known how this affected Somerset. The Western Wandsdyke may have been constructed in this period but archaeological data shows that it was probably built during the 5th or 6th century. This area became the border between the Romano-British Celts and the West Saxons following the Battle of Deorham in 577 AD. The ditch is on the north side, so presumably it was used by the Celts as a defence against Saxons encroaching from the upper Thames Valley. According to the Anglo-Saxon Chronicle, the Saxon Cenwalh achieved a breakthrough against the British Celtic tribes, with victories at Bradford-on-Avon (in the Avon Gap in the Wansdyke) in 652 AD, and further south at the Battle of Peonnum (at Penselwood) in 658 AD, followed by an advance west through the Polden Hills to the River Parrett.

The Saxon advance from the east seems to have been halted by battles between the British and Saxons, for example; at the siege of Badon Mons Badonicus (which may have been in the Bath region e.g. at Solsbury Hill), or Bathampton Down. During the 5th, 6th and 7th centuries, Somerset was probably partly in the Kingdom of Dumnonia, partly in the land of the Durotriges and partly in that of the Dobunni. The boundaries between these is largely unknown, but may have been similar to those in the Iron Age. Various "tyrants" seem to have controlled territories from reoccupied hill forts. There is evidence of an elite at hill forts such as Cadbury Castle and Cadbury Camp; for example, there is imported pottery. Cemeteries are an important source of evidence for the period and large ones have been found in Somerset, such as that at Cannington, which was used from the Roman to the Saxon period. The towns of Somerset seem to have been little used during that period but there continued to be farming on the villa sites and at the Romano-British villages.

There may have been effects from plague and volcanic eruption during this period as well as marine transgression into the Levels.

The language spoken during this period is thought to be Southwestern Brythonic, but only one or two inscribed stones survive in Somerset from this period. However, a couple of curse tablets found in the baths at Bath may be in this language. Some place names in Somerset seem to be Celtic in origin and may be from this period or earlier, e.g. Tarnock. Some river names, such as Parrett, may be Celtic or pre-Celtic. The religion of the people of Somerset in this period is thought to be Christian but it was isolated from Rome until after the Council of Hertford in 673 AD when Aldhelm was asked to write a letter to Geraint of Dumnonia and his bishops. Some church sites in Somerset are thought to date from this period, e.g., Llantokay Street.

Most of what is known of the history of this period comes from Gildas's On the Ruin of Britain, which is thought to have been written in Durotrigan territory, possibly at Glastonbury.

The earliest fortification of Taunton started for King Ine of Wessex and Æthelburg, in or about the year 710 AD. However, according to the Anglo-Saxon Chronicle this was destroyed 12 years later.

Early Medieval
This is the period from the late 7th century (for most of Somerset) to 1066, though for part of the 10th and 11th centuries England was under Danish control. Somerset, like Dorset to the south, held the West Saxon advance from Wiltshire/Hampshire back for over a century, remaining a frontier between the Saxons and the Romano-British Celts.

The Saxons conquered Bath following the Battle of Deorham in 577, and the border was probably established along the line of the Wansdyke to the north of the Mendip Hills. Then Cenwalh of Wessex broke through at Bradford-on-Avon in 652, and the Battle of Peonnum possibly at Penselwood in 658, advancing west through the Polden Hills to the River Parrett. In 661 the Saxons may have advanced into what is now Devon as a result of a battle fought at Postesburh, possibly Posbury near Crediton.

Then in the period 681–85 Centwine of Wessex conquered King Cadwaladr and "advanced as far as the sea", but it is not clear where this was. It is assumed that the Saxons occupied the rest of Somerset about this time. The Saxon rule was consolidated under King Ine, who established a fort at Taunton, demolished by his wife in 722. It is sometimes said that he built palaces at Somerton and South Petherton but this does not seem to be the case. He fought against Geraint in 710. In 705 the diocese of Sherborne was formed, taking in Wessex west of Selwood. Saxon kings granted land in Somerset by charter from the 7th century onward. The way and extent to which the Britons survived under the Saxons is a debatable matter. However, King Ine's laws make provision for Britons. Somerset originally formed part of Wessex and latter became a separate "shire". Somersetshire seems to have been formed within Wessex during the 8th century though it is not recorded as a name until later. Mints were set up at times in various places in Somerset in the Saxon period, e.g., Watchet.

Somerset played an important part in defeating the spread of the Danes in the 9th century. The Anglo-Saxon Chronicle records that in 845 Alderman Eanwulf, with the men of Somersetshire (Sumorsǣte), and Bishop Ealstan, and Alderman Osric, with the men of Dorsetshire, conquered the Danish army at the mouth of the Parret. This was the first known use of the name Somersæte. The Anglo-Saxon Chronicle reports that in January 878 the King Alfred the Great fled into the marshes of Somerset from the Viking's invasion and made a fort at Athelney. From the fort Alfred was able to organize a resistance using the local militias from Somerset, Wiltshire and Hampshire.

Viking raids took place for instance in 987 and 997 at Watchet and the Battle of Cynwit. King Alfred was driven to seek refuge from the Danes at Athelney before defeating them at the Battle of Ethandun in 878, usually considered to be near Edington, Wiltshire, but possibly the village of Edington in Somerset. Alfred established a series of forts and lookout posts linked by a military road, or Herepath, so his army could cover Viking movements at sea. The Herepath has a characteristic form which is familiar on the Quantocks: a regulation 20 m wide track between avenues of trees growing from hedge laying embankments. The Herepath ran from the ford on the River Parrett at Combwich, past Cannington hill fort to Over Stowey, where it climbed the Quantocks along the line of the current Stowey road, to Crowcombe Park Gate. Then it went south along the ridge, to Triscombe Stone. One branch may have led past Lydeard Hill and Buncombe Hill, back to Alfred's base at Athelney. The main branch descended the hills at Triscombe, then along the avenue to Red Post Cross, and west to the Brendon Hills and Exmoor. A peace treaty with the Danes was signed at Wedmore and the Danish king Guthrum the Old was baptised at Aller. Burhs (fortified places) had been set up by 919, such as Lyng. The Alfred Jewel, an object about 2.5 inch long, made of filigree gold, cloisonné-enamelled and with a rock crystal covering, was found in 1693 at Petherton Park, North Petherton. Believed to have been owned by Alfred the Great it is thought to have been the handle for a pointer that would have fit into the hole at its base and been used while reading a book.

Monasteries and minster churches were set up all over Somerset, with daughter churches from the minsters in manors. There was a royal palace at Cheddar, which was used at times in the 10th century to host the Witenagemot, and there is likely to have been a "central place" at Somerton, Bath, Glastonbury and Frome since the kings visited them. The towns of Somerset seem to have been in occupation in this period though evidence for this is limited because of subsequent buildings on top of remains from this period. Agriculture flourished in this period, with a re-organisation into centralised villages in the latter part in the east of the county.

In the period before the Norman Conquest, Somerset came under the control of Godwin, Earl of Wessex, and his family. There seems to have been some Danish settlement at Thurloxton and Spaxton, judging from the place-names. After the Norman Conquest, the county was divided into 700 fiefs, and large areas were owned by the crown, with fortifications such as Dunster Castle used for control and defence.

This period of Somerset's history is well documented, for example in the Anglo-Saxon Chronicle and Asser's Life of Alfred.

Later Medieval
This is the period from 1066 to around 1500. Following the defeat of the Saxons by the Normans in 1066, various castles were set up in Somerset by the new lords such as that at Dunster, and the manors was awarded to followers of William the Conqueror such as William de Moyon and Walter of Douai. Somerset does not seem to have played much part in the civil war in King Stephen's time, but Somerset lords were main players in the murder of Thomas Becket.

A good picture of the county in 1086 is given by Domesday Book, though there is some difficulty in identifying the various places since the hundreds are not specified. The total population given for the county, which had different boundaries to those today, was 13,399, however this only included the heads of households, so with their families this may have been around 67,000. Farming seems to have prospered for the next three centuries but was severely hit by the Black Death which in 1348 arrived in Dorset and quickly spread through Somerset, causing widespread mortality, perhaps as much as 50% in places. It re-occurred, resulting in a change in feudal practices since the manpower was no longer so available.

Reclamation of land from marsh in the Somerset Levels increased, largely under monastic influence. Crafts and industries also flourished, the Somerset woollen industry being one of the largest in England at this time. "New towns" were founded in this period in Somerset, i.e. Newport, but were not successful. Coal mining on the Mendips was an important source of wealth while quarrying also took place, an example is near Bath.

The towns grew, again often by monastic instigation, during this period and fairs were started. The church was very powerful at this period, particularly Glastonbury Abbey. After their church burnt down, the monks there "discovered" the tomb of "King Arthur" and were able rebuild their church. There were over 20 monasteries in Somerset at this period including the priory at Hinton Charterhouse which was founded in 1232 by Ela, Countess of Salisbury who also founded Lacock Abbey. Many parish churches were re-built in this period. Between 1107 and 1129 William Giffard the Chancellor of King Henry I, converted the bishop's hall in Taunton into Taunton Castle. Bridgwater Castle was built in 1202 by William Brewer. It passed to the king in 1233 and in 1245 repairs were ordered to its motte and towers. During the 11th century Second Barons' War against Henry III, Bridgwater was held by the barons against the King. In the English Civil War the town and the castle were held by the Royalists under Colonel Sir Francis Wyndham. Eventually, with many buildings destroyed in the town, the castle and its valuable contents were surrendered to the Parliamentarians. The castle itself was deliberately destroyed in 1645.

During the Middle Ages sheep farming for the wool trade came to dominate the economy of Exmoor. The wool was spun into thread on isolated farms and collected by merchants to be woven, fulled, dyed and finished in thriving towns such as Dunster. The land started to be enclosed and from the 17th century onwards larger estates developed, leading to establishment of areas of large regular shaped fields. During this period a Royal Forest and hunting ground was established, administered by the Warden. The Royal Forest was sold off in 1818.

In the medieval period the River Parrett was used to transport Hamstone from the quarry at Ham Hill, Bridgwater was part of the Port of Bristol until the Port of Bridgwater was created in 1348, covering 80 mi of the Somerset coast line, from the Devon border to the mouth of the River Axe. Historically, the main port on the river was at Bridgwater; the river being bridged at this point, with the first bridge being constructed in 1200 AD. Quays were built in 1424; with another quay, the Langport slip, being built in 1488 upstream of the Town Bridge. A Customs House was sited at Bridgwater, on West Quay; and a dry dock, launching slips and a boat yard on East Quay. The river was navigable, with care, to Bridgwater Town Bridge by 400 to 500 tonne vessels. By trans-shipping into barges at the Town Bridge the Parrett was navigable as far as Langport and (via the River Yeo) to Ilchester.

Early Modern
This is the period from around 1500 to 1800. In the 1530s, the monasteries were dissolved and their lands bought from the king by various important families in Somerset. By 1539, Glastonbury Abbey was the only monastery left, its abbot Richard Whiting was then arrested and executed on the orders of Thomas Cromwell. From the Tudor to the Georgian times, farming specialised and techniques improved, leading to increases in population, although no new towns seem to have been founded. Large country houses such as at Hinton St George and Montacute House were built at this time.

The Bristol Channel floods of 1607 are believed to have affected large parts of the Somerset Levels with flooding up to 8 ft above sea level. In 1625, a House of Correction was established in Shepton Mallet and, today, HMP Shepton Mallet is England's oldest prison still in use.

During the English Civil War, Somerset was largely Parliamentarian, although Dunster was a Royalist stronghold. The county was the site of important battles between the Royalists and the Parliamentarians, notably the Battle of Lansdowne in 1643 and the Battle of Langport in 1645. The castle changed hands several times during 1642–45 along with the town. During the Siege of Taunton it was defended by Robert Blake, from July 1644 to July 1645. This war resulted in castles being destroyed to prevent their re-use.

In 1685, the Duke of Monmouth led the Monmouth Rebellion in which Somerset people fought against James II. The rebels landed at Lyme Regis and travelled north hoping to capture Bristol and Bath, puritan soldiers damaged the west front of Wells Cathedral, tore lead from the roof to make bullets, broke the windows, smashed the organ and the furnishings, and for a time stabled their horses in the nave. They were defeated in the Battle of Sedgemoor at Westonzoyland, the last battle fought on English soil. The Bloody Assizes which followed saw the losers being sentenced to death or transportation.

The Society of Friends established itself in Street in the mid-17th century, and among the close-knit group of Quaker families were the Clarks: Cyrus started a business in sheepskin rugs, later joined by his brother James, who introduced the production of woollen slippers and, later, boots and shoes. C&J Clark still has its headquarters in Street, but shoes are no longer manufactured there. Instead, in 1993, redundant factory buildings were converted to form Clarks Village, the first purpose-built factory outlet in the United Kingdom.

The 18th century was largely one of peace and declining industrial prosperity in Somerset. The Industrial Revolution in the Midlands and Northern England spelt the end for most of Somerset's cottage industries. However, farming continued to flourish, with the Bath and West of England Agricultural Society being founded in 1777 to improve methods. John Billingsley conducted a survey of the county's agriculture in 1795 but found that methods could still be improved.

Arthur Wellesley took his title, Duke of Wellington from the town of Wellington. He is commemorated on a nearby hill with a large, spotlit obelisk, known as the Wellington Monument.

In north Somerset, mining in the Somerset coalfield was an important industry, and in an effort to reduce the cost of transporting the coal the Somerset Coal Canal was built; part of it was later converted into a railway. Other canals included the Bridgwater and Taunton Canal, Westport Canal, Grand Western Canal, Glastonbury Canal and Chard Canal. The Dorset and Somerset Canal was proposed, but very little of it was ever constructed.

Late Modern
The 19th century saw improvements to Somerset's roads with the introduction of turnpikes and the building of canals and railways. The usefulness of the canals was short-lived, though they have now been restored for recreation. The railways were nationalised after the Second World War, but continued until 1965, when smaller lines were scrapped; two were transferred back to private ownership as "heritage" lines.

In 1889, Somerset County Council was created, replacing the administrative functions of the Quarter Sessions.

The population of Somerset has continued to grow since 1800, when it was 274,000, particularly in the seaside towns such as Weston-super-Mare. Some population decline occurred earlier in the period in the villages, but this has now been reversed, and by 1951 the population of Somerset was 551,000.

Chard claims to be the birthplace of powered flight, as it was here in 1848 that the Victorian aeronautical pioneer John Stringfellow first demonstrated that engine-powered flight was possible through his work on the Aerial Steam Carriage. North Petherton was the first town in England (and one of the few ever) to be lit by acetylene gas lighting, supplied by the North Petherton Rosco Acetylene Company. Street lights were provided in 1906. Acetylene was replaced in 1931 by coal gas produced in Bridgwater, as well as by the provision of an electricity supply.

Around the 1860s, at the height of the iron and steel era, a pier and a deep-water dock were built, at Portishead, by the Bristol & Portishead Pier and Railway to accommodate the large ships that had difficulty in reaching Bristol Harbour. The Portishead power stations were coal-fed power stations built next to the dock. Construction work started on Portishead "A" power station in 1926. It began generating electricity in 1929 for the Bristol Corporation's Electricity Department. In 1951, Albright and Wilson built a chemical works on the opposite side of the dock from the power stations. The chemical works produced white phosphorus from phosphate rock imported, through the docks, into the UK. The onset of new generating capacity at Pembroke (oil-fired) and Didcot (coal-fired) in the mid-1970s brought about the closure of the older, less efficient "A" Station. The newer of the two power stations ("B" Station) was converted to burn oil when the Somerset coalfields closed. Industrial activities ceased in the dock with the closure of the power stations. The Port of Bristol Authority finally closed the dock in 1992, and it has now been developed into a marina and residential area.

During the First World War hundreds of Somerset soldiers were killed, and war memorials were put up in most of the towns and villages; only a few villages escaped casualties. There were also casualties – though much fewer – during the Second World War, who were added to the memorials. The county was a base for troops preparing for the 1944 D-Day landings, and some Somerset hospitals still date partly from that time. The Royal Ordnance Factory ROF Bridgwater was constructed early in World War II for the Ministry of Supply. It was designed as an Explosive ROF, to produce RDX, which was then a new experimental high-explosive. It obtained water supplies from two sources via the Somerset Levels: the artificial Huntspill River which was dug during the construction of the factory and also from the King's Sedgemoor Drain, which was widened at the same time. The Taunton Stop Line was set up to resist a potential German invasion, and the remains of its pill boxes can still be seen, as well as others along the coast. A decoy town was constructed on Black Down, intended to represent the blazing lights of a town which had neglected to follow the black-out regulations. Sites in the county housed Prisoner of War camps including: Norton Fitzwarren, Barwick, Brockley, Goathurst and Wells. Various airfields were built or converted from civilian use including: RNAS Charlton Horethorne (HMS Heron II), RAF Weston-super-Mare, RNAS Yeovilton (HMS Heron), Yeovil/Westland Airport, RAF Weston Zoyland, RAF Merryfield, RAF Culmhead and RAF Charmy Down.

Exmoor was one of the first British National Parks, designated in 1954, under the 1949 National Parks and Access to the Countryside Act. and is named after its main river. It was expanded in 1991 and in 1993 Exmoor was designated as an Environmentally Sensitive Area. The Quantock Hills were designated as an Area of Outstanding Natural Beauty (AONB) in 1956, the first such designation in England under the National Parks and Access to the Countryside Act 1949. The Mendip Hills followed with AONB designation in 1972.

Hinkley Point A nuclear power station was a Magnox power station constructed between 1957 and 1962 and operating until ceasing generation in 2000. Hinkley Point B is an Advanced Gas-cooled Reactor (AGR) which was designed to generate 1250 MW of electricity (MWe). Construction of Hinkley Point B started in 1967. In September 2008 it was announced, by Électricité de France (EDF), that a third, twin-unit European Pressurised Reactor (EPR) power station known as Hinkley Point C is planned, to replace Hinkley Point B which was due for closure in 2016, but has now has its life extended until 2022.

Somerset today has only two small cities, Bath and Wells, and only small towns in comparison with other areas of England. Tourism is a major source of employment along the coast, and in Bath and Cheddar for example. Other attractions include Exmoor, West Somerset Railway, Haynes Motor Museum and the Fleet Air Arm Museum as well as the churches and the various National Trust and English Heritage properties in Somerset.

Agriculture continues to be a major business, if no longer a major employer because of mechanisation. Light industries take place in towns such as Bridgwater and Yeovil. The towns of Taunton and Shepton Mallet manufacture cider, although the number of apple orchards has reduced.

In the late 19th century the boundaries of Somerset were slightly altered, but the main change came in 1974 when the county of Avon was set up. The northern part of Somerset was removed from the administrative control of Somerset County Council. On abolition of the county of Avon in 1996, these areas became separate administrative authorities, "North Somerset" and "Bath and North East Somerset". The Department for Communities and Local Government was considering a proposal by Somerset County Council to change Somerset's administrative structure by abolishing the five districts to create a Somerset unitary authority. The changes were planned to be implemented no later than 1 April 2009. However, support for the county council's bid was not guaranteed and opposition among the district council and local population was strong; 82% of people responding to a referendum organised by the five district councils rejected the proposals. It was confirmed in July 2007 that the government had rejected the proposals for unitary authorities in Somerset, and that the present two-tier arrangements of Somerset County Council and the district councils will remain.

title: History of Somerset


text:
Borrowed chord

A borrowed chord (also called mode mixture, modal mixture, substituted chord, modal interchange, or mutation ) is a chord borrowed from the parallel key (minor or major scale with the same tonic). Borrowed chords are typically used as "color chords", providing harmonic variety through contrasting scale forms, which are major scales and the three forms of minor scales. Chords may also be borrowed from other parallel modes besides the major and minor mode, for example D Dorian with D major. The mixing of the major and minor modes developed in the Baroque period.

Borrowed chords are distinguished from modulation by being brief enough that the tonic is not lost or displaced, and may be considered brief or transitory modulations and may be distinguished from secondary chords as well as altered chords. According to Sheila Romeo, "[t]he borrowed chord suggests the sound of its own mode without actually switching to that mode."

Common borrowed chords
Sheila Romeo explains that "[i]n theory, any chord from any mode of the scale of the piece is a potential modal interchange or borrowed chord. Some are used more frequently than others, while some almost never occur."

In the minor mode, a common borrowed chord from the parallel major key is the Picardy third.

In the major mode, the most common examples of borrowed chords are those involving the ♭, also known as the lowered sixth scale degree. These chords are shown below, in the key of C major. The next most common involve the ♭ and ♭. These chords are shown below.

Chord progressions may be constructed with borrowed chords, including two progressions common in rock music, I–♭VII–♭VI–♭VII, common everywhere, and I–♭VI–IV, used by bands like Genesis, Yes, and Nirvana. ♭VII is from Mixolydian and ♭VI is found in both Aeolian and Phrygian. The ♭VII–I cadence with ♭VII substituting for V is common, as well as ♭II–I, ♭III–I, and ♭VI–I. In popular music, the major triads on the lowered third (♭III), sixth (♭VI) and seventh (♭VII) scale degrees are common.

Borrowed chords have typical inversions or common positions, for example ii6 and ii$7$, and progress in the same manner as the diatonic chords they replace except for ♭VI, which progresses to V(7).

title: Borrowed chord


text:
Xero (band)

Xero (also styled as Zero or Xiro) were an Australian punk rock and new wave band formed in 1978 in Brisbane, Queensland. They were fronted by mainstay member, Irena Luckus on lead vocals, keyboards and guitar before disbanding in 1983.

History
Zero were formed in Brisbane in 1977 with the initial line-up of Peter Adams on guitar and vocals; Chris Anderson on guitar and vocals; Jude Clarkin on bongos; Barbara Hart on saxophone and flute; John Hunt on bass guitar; Irena Luckus on vocals, keyboard and guitar; and Debbie Penny on drums. By 1978, now including Vic Allen, Deborah Thomas and Lindy Morrison, the band travelled across New South Wales by train, playing gigs in Canberra (in a large, very cold hall) and Newcastle (in a local pub). In 1979 the group settled as a four-piece with Luckus, Morrison, John Willsteed and Michael O'Connell, and among a number of significant gigs, opened for The Cure in support of that group's second album, Seventeen Seconds. The Go-Betweens Robert Forster was an occasional guest, and when Morrison left in September 1980 to join Forster and Grant McLennan, O'Connell also left, moving to Sydney to play in a number of bands. Zero then became Xiro, and decided on the Roland DR-55 as a suitable drummer replacement.

Xiro issued two different four-track extended plays, Half the Profits and Religious Wars, on audio cassette in mid-1980. They supported The Cure again in 1981, with guest and future Xero drummer Steven Pritchard. Luckus and Willsteed were then joined by Clare McKenna on drums to become Xero and entered a period of intense song-writing in their Fortitude Valley practice rooms, and performing at various Brisbane venues. In 1982 Xero recorded a six-track extended play, Lust in the Dust, at Basement Studios, Brisbane with the line-up of Luckus, Tony Childs on bass guitar; John Willsteed on bass guitar, guitar, casio keyboards and vocals; and Steven Pritchard on drums.

Xero split in 1983 when Luckus left Brisbane to relocate to France. Later, Morrison and Willsteed were members of fellow Brisbane group, the Go-Betweens. O'Connell and Willsteed were both members of the Apartments. They have reformed for gigs since then, initially in 1986.

Members

 * Irena Luckus– vocals, keyboard, guitar (1978–84)
 * Chris Anderson– guitar, vocals (1978)
 * Peter Adams– guitar, vocals (1978)
 * Debbie Penny– drums (1978)
 * John Hunt– bass guitar (1978)
 * Barbara Hart– saxophone, flute (1978)
 * Jude Clarkin– bongos (1978)
 * Vic Allen (aka Nicki Nought)– guitar (1979)
 * Deborah Thomas (aka Debbie Zero)– guitar (1979)
 * John Willsteed (aka John e)– bass guitar (1979–84), vocals (1980–84) , guitar and keyboards (1981–84)
 * Lindy Morrison– drums (1979–80)
 * Robert Forster– guitar, vocals (1979)
 * Michael O'Connell– guitar, vocals (1979-1980)
 * Clare McKenna– drums, bass guitar, vocals (1980-1981)
 * Mal Skewis– vocals (auxiliary live musician, 1980-1981)
 * Gary Warner– vocals, soprano saxophone (auxiliary live musician, 1980-1981)
 * Colin Bloxsom– guitar (auxiliary live musician, 1980-1981)
 * Steven Pritchard– drums (1981-1982)
 * Tony Childs– bass guitar (1982)
 * Tony Milner– guitar (1983)

Timeline

Discography

 * Half the Profits (as Xiro) cassette EP (independent, July 1980)
 * Religious Wars (as Xiro) cassette EP (independent, July 1980)
 * Lust in the Dust (as Xero) 12" EP (M-Squared, 1982)
 * Xiro Live at the Cement Box Theatre CD (Ten of Cups, 1998)

title: Xero (band)


text:
Ziro

Ziro is a town in and the district headquarters of the Lower Subansiri district in the Indian state of Arunachal Pradesh. It is included the Tentative List for UNESCO's World Heritage Site for the Apatani cultural landscape. The part of the town which is the centre of economic activities and where the administrative offices are located is called as Hapoli or locally known by the Apatanis as "Hao-Polyang".

Ziro is 115 km from the state capital, Itanagar, 112 km from North Lakhimpur in Assam and 96 km from Naharlagun railway station. Indian Air Force's ALG airstrip is at Ziro.

Geography
Ziro is the district headquarter of Lower Subansiri district and is one of the oldest towns in Arunachal Pradesh. It is located at 27.63°N, 93.83°W at an elevation of 1688 metres (5538 feet) to 2438 meters (8000 feet). Its cool weather in summer is its major attraction.

It is famous for its surrounding pine-clad gentle hills and its rice fields. Ziro is home to the Apatani tribe.

Road
Ziro is around 115 km from the state capital, Itanagar and takes approx. three and a half hours by road, via the improved Hoj-Potin road, along NH-229, and 150 km via the Assam route.

Rail
The nearest railway station from Ziro is located at Naharlagun, near the Arunachal-Assam border, which is around 100 km from Ziro.

Air
The nearest airport to Ziro is Ziro Airport, which is an Advanced Landing Ground (ALG) of the Indian Air Force, and along with it, flights are operated by Alliance Air. It is located in the main town of old Ziro. Other main and major airports lying in proximity to Ziro are North Lakhimpur in Assam (116 km) and Itanagar (133 km).

Climate
The climatic condition of the district varies from place to place as well as season to season. Its climate is largely influenced by the nature of terrain depending upon altitude and location of the place. It could be broadly be divided into four seasons in a year:

 * 1) The cold weather season is from December to February
 * 2) March to May is the pre-monsoon season of thunderstorms
 * 3) The southwest monsoon from June to about the middle of October
 * 4) The second half of October to November, which constitutes the post-monsoon or the retreating monsoon period and is a period of transition

In the foothills or low high belt area of the district, the climatic condition is moderate in comparison to high belt areas, where during winter it is very cold and chilly, and in summer is pleasant. December and January are generally the coldest months, and July and August are warmest months.

Annual rainfall in the south is heavier than that in the northern areas of the district. During the monsoon period, more than 70 percent of the rain over the southern half occurs while in the northern portions it is about 60 percent. Variability of rainfall for the monsoon and the year, as a whole, are relatively small. Average annual rainfall of the district headquarters, Ziro recorded as 934.88 cm during 2000.

The relative humidity is always high throughout the year except in the winter months being slightly less humid. In the cold season, the sky is obscured on many mornings due to lifted fog which clears with the advance of the day generally, moderately clouded in the period of March to May, heavily clouded to overcast in the monsoon season and clear or slightly clouded during the post-monsoon season. Winds are generally light strong katabatic winds down the valleys are experienced as the local effect produced by the nature of the terrain.

Demography
India census, Ziro had a population of 12,806. Males constitute 50% of the population and females 50%. In Ziro, 17% of the population is under 6 years of age.

Languages
According to 2011 census, Apatani was the most spoken language in Ziro with 10,867 speakers followed by Bengali at 1,104, Assamese at 752, Nepali at 746, Bhojpuri at 728 and Hindi at 395.

Apatani culture
Apatanis have few unique special characteristic features which differ from other tribes in Arunachal Pradesh and India. Few of these special characteristic features are:

(A) Apatanis practice permanent wet paddy cultivation whereas other tribes practice shifting cultivation called Jhom cultivation. (B) Apatanis cultivate permanent wet land cultivations whereas other tribes practice dry land cultivations by clearing the forests by burning the jungles. (C) Apatanis once practiced the art of facial tattoos.

UNESCO world heritage cultural sites

Apatani cultural landscape in Ziro Valley in Lower Subansiri district and Thembang Dzong in West Kameng district have been included in the Tentative List for UNESCO's World Heritage Site. The Arunachal Pradesh government has undertaken conservation works at these sites with the aim of ensuring inclusion of these sites in UNESCO's final list. Apatani cultural landscape comprises 32 sq km2 cultivable areas out of 1058 km2 plateau. Apatani tribe, which has inhabited this region for centuries, is known for practicing ecologically sustainable existential sustenance. Thembang Dzong is a 3.2 acres fortified village of Monpa tribe.

Education
Ziro has one university and one undergraduate arts college namely Indira Gandhi Technological and Medical Sciences University and Saint Claret College respectively. As of the 2001 census, Ziro had an average literacy rate of 66%, lower than the national average of 74.04%: male literacy was 72%, and female literacy was 60%. The older generation hadn't been exposed to formal education, but with the rapid pace of education of younger generations, the education scenario of Ziro grew tremendously and is poised to grow further.

Urban populace of Lower Subansiri district mainly reside in Ziro and as per 2011 census, average urban literacy rate in Lower Subansiri district is 85.52% of which males and females are 89.81% and 81.26% literates respectively. It is worth noting that, as per the 2011 census, 84.58% population of Lower Subansiri districts lives in rural areas of villages. The literacy rate in rural areas of Lower Subansiri district is 72.27%. Still, the combined literacy rate is 74.35%, which is second in Arunachal Pradesh, next only to Papumpare District where the capital city of Itanagar is located.

Notable People
Robin Hibu - Special Commissioner, Delhi Police

title: Ziro


text:
Huntley

Huntley may refer to:

Australia

 * Huntley, New South Wales (Orange), in City of Orange
 * Huntley, New South Wales (Wollongong), a suburb of Wollongong, New South Wales

Canada

 * Huntley, Prince Edward Island
 * Huntley Township, Ontario

England

 * Huntley, Gloucestershire
 * Huntley, Staffordshire, a UK location

United States

 * Huntley, Illinois
 * Huntley, Minnesota
 * Huntley, Montana
 * Huntley, Nebraska
 * Huntley, Wyoming

Other uses

 * Huntley (name)
 * Huntley (plantation) near Washington, DC
 * Huntley Project, an irrigation project in southern Montana 1907
 * Huntley & Palmers, notable British firm of biscuit makers
 * Huntley School, New Zealand

title: Huntley


text:
User talk:P23~enwiki

Hi Mike. You say: "and you can't write worth shit. I'd fail you if I were a professor". To judge from the "you can't write worth shit", the proposition "if I were a professor" is not very likely, is it? I think I can breath easy. --Tagishsimon

You know, Mike, people would respect you more if you were honest, or at very least if you didn't act like we're all stupid. Maybe I couldn't prove in court that this is you, but that doesn't mean I'm fooled for an instant, and neither is anyone else. Didn't you notice that you can check the contributions of other users? P23 has only made three edits, and all of them were about you. That's about as obvious a sock puppet as I've ever seen.

Why do you bother? Chef Lord, P23, and AFK are all you. You and I both know it. The point is, editing from obvious sock puppet accounts only makes you look dishonest, since you don't fool anyone. Please pick a single account and stick with it. Tagishsimon's comments to you weren't nice, but you could have stood up like a man and answered him with your own identity. Isomorphic 01:47, 12 May 2004 (UTC)

User_talk:Tagishsimon
Pot kettle black! Let me remind you that we have a strict policy of no personal attacks here. How can you chastise someone for their comments on Mike Church's talk page then do much the same on their talk page?

I'm guessing here but I suspect you allowed your anger to get in the way of your better judgement. We all do that, I've done it a number of times myself but I usually manage to hit delete instead of save (thank God). Anyway, the best thing to do is not reply straight away. Sleep on it, calm down and post a polite yet to the point comment the next day. theresa knott 08:30, 12 May 2004 (UTC)

Your account will be renamed
Hello,

The developer team at Wikimedia is making some changes to how accounts work, as part of our on-going efforts to provide new and better tools for our users like cross-wiki notifications. These changes will mean you have the same account name everywhere. This will let us give you new features that will help you edit and discuss better, and allow more flexible user permissions for tools. One of the side-effects of this is that user accounts will now have to be unique across all 900 Wikimedia wikis. See the announcement for more information.

Unfortunately, your account clashes with another account also called P23. To make sure that both of you can use all Wikimedia projects in future, we have reserved the name P23~enwiki that only you will have. If you like it, you don't have to do anything. If you do not like it, you can pick out a different name. If you think you might own all of the accounts with this name and this message is in error, please visit Special:MergeAccount to check and attach all of your accounts to prevent them from being renamed.

Your account will still work as before, and you will be credited for all your edits made so far, but you will have to use the new account name when you log in.

Sorry for the inconvenience.

Yours, Keegan Peterzell Community Liaison, Wikimedia Foundation 02:16, 20 March 2015 (UTC)

Renamed
 This account has been renamed as part of single-user login finalisation. If you own this account you can |log in using your previous username and password for more information. If you do not like this account's new name, you can choose your own using this form after logging in: . -- Keegan (WMF) (talk) 17:21, 22 April 2015 (UTC)

title: User talk:P23~enwiki


text:
Lowndean Professor of Astronomy and Geometry

The Lowndean chair of Astronomy and Geometry is one of the two major Professorships in Astronomy (alongside the Plumian Professorship) and a major Professorship in Mathematics at Cambridge University. It was founded in 1749 by Thomas Lowndes, an astronomer from Overton in Cheshire.

The original bequest stated that the holder must give two courses of twenty lectures each year, one in astronomy, and the other in geometry, and spend at least six weeks making astronomical observations.

Originally the holder was elected by a committee consisting of the Lord Chancellor, the Lord President of the Privy Council, the Lord Privy Seal, the Lord Steward of the Household, and the Lord High Treasurer of the First Lord of the Treasury.

By the 20th century, the electors had changed to comprise the most senior scientists in the United Kingdom: the President of the Royal Society, the President of the Royal Astronomical Society, the Astronomer Royal, the Vice Chancellor of the University of Cambridge, and the Lucasian, Sadleirian, and Plumian Professors.

Notwithstanding the title, a professor can be chosen who specializes solely or chiefly in only one, rather than both, of the subjects of astronomy and geometry.

Lowndean Professors

 * 1750–1771 Roger Long
 * 1771–1795 John Smith
 * 1795–1837 William Lax
 * 1837–1859 George Peacock
 * 1859–1892 John Couch Adams
 * 1892–1913 Robert Stawell Ball
 * 1914–1936 H. F. Baker
 * 1936–1970 W. V. D. Hodge
 * 1970–1989 J. Frank Adams
 * 1990–1999 Graeme Segal
 * 2000–2014 Burt Totaro
 * 2015-present Mihalis Dafermos


text:
File:Fadoemmim.jpg

Summary
Mariza's "Fado em Mim" album cover.

title: File:Fadoemmim.jpg


text:
Talk:Relative key

List vs. table
I think the list would look much better as a table, but feel that others may object as it is simply a list and may not be appropriate. Is there another method we could use to align the relative keys. Hyacinth 23:03, 11 May 2004 (UTC)

 * We could preformat it, I suppose:

C major   A minor G major   E minor D major   B minor

 * but that's kind of ugly. I think a table should be fine, myself. Alternatively, we could do something clever with the circle of fifths image, putting the major keys on the outside of the circle and their relative minors on the inside. Just a passing thought, probably not worth the hassle, really. --Camembert

Capitalization
Aren't minor key names normally left uncapitalized? Right now, throughout the whole article, the names are capitalized. --Iammisc —Preceding comment was added at 03:38, 2 February 2008 (UTC)

 * My understanding is no, not if it is followed by the word "minor" for example "E minor". Note minor chords for guitar follow this rule for example "E min". Lower case letters (by themselves) are sometimes used as shorthand for minor.--Dbolton (talk) 08:38, 2 February 2008 (UTC)

Purpose?
I fail to see the purpose of relative keys. I understand the concept, I just don't know how or why anyone would use it. —Preceding unsigned comment added by 71.101.234.25 (talk) 22:38, 17 June 2008 (UTC)

 * Well, I don't have a wonderfully firm grasp on it, but it's basically a quick way to derive a minor key from a major key or a major from a minor. Even though they are the same, they're still distinctly different in the way they sound. Maybe I'm wrong but I don't think I'm too far off.DL (talk) 19:10, 10 November 2008 (UTC)

How can they sound different when they are the same? I'd like this explained also... —Preceding unsigned comment added by 83.226.99.55 (talk) 22:55, 8 February 2010 (UTC)

 * They are not the same. There are two important characteristics of major and minor scales (like men's pants): the tonic and the key signature (instead of length and waist). A major scale which is relative to a minor scale is different in that it hays a different tonic, but similar in that it has the same key signature. Contrastingly, a major scale which is parallel to a minor scale has a different key signature, but the same tonic. Hyacinth (talk) 09:15, 15 March 2010 (UTC)

Regarding purpose, my recent addition begins to address this: "Relative keys are closely related keys, in that they differ by no more than one accidental (none in the case of relative keys), the keys between which most modulations occur." Hyacinth (talk) 06:05, 21 March 2010 (UTC)

 * See also the recently added image of a modulation between relative keys. Hyacinth (talk) 10:20, 21 March 2010 (UTC)

Image copyright problem with File:Ayumi Hamasaki - M.ogg
The image File:Ayumi Hamasaki - M.ogg is used in this article under a claim of fair use, but it does not have an adequate explanation for why it meets the requirements for such images when used here. In particular, for each page the image is used on, it must have an explanation linking to that page which explains why it needs to be used on that page. Please check

 * That there is a non-free use rationale on the image's description page for the use in this article.
 * That this article is linked to from the image description page.

This is an automated notice by FairuseBot. For assistance on the image use policy, see Media copyright questions. --15:18, 2 March 2009 (UTC)

Reqmusic
I've added an audio example, though a more "musical" one would be informative. Hyacinth (talk) 08:05, 20 March 2010 (UTC)

 * Done. Hyacinth (talk) 10:20, 21 March 2010 (UTC)

Relative vs closely related
The last sentence of the first paragraph seems to contradict itself (particularly the section in parentheses). Can a relative keys still be considered closely related keys if they vary not at all? JlnMyr (talk) 18:05, 9 May 2012 (UTC)

"Relative keys are closely related keys, in that they differ by no more than one accidental (none in the case of relative keys), the keys between which most modulations occur.": I believe the parentheses part is a typo. logically it seems like it should say "(none in the case of parallel keys)" 69.117.164.197 (talk) 20:34, 6 March 2013 (UTC)

Incomprehensible
Minimal knowledge is required to even start to understand this material, of which I have none. — Preceding unsigned comment added by Longinus876 (talk • contribs) 14:10, 23 July 2019 (UTC)

title: Talk:Relative key