pascal

unit of energy measurement

In the metric-kilogram-second system (the International System of Units [SI]), a pascal is a unit of pressure and stress. Pascal was a French mathematician and physicist who lived between 1623 and 1662. In SI units, a pascal equals one newton per square meter, or one kilogram per meter per second squared. The kilopascal (kPa) of 1,000 newtons per square metre is more commonly used since it is more convenient for many purposes. One atmosphere (or 101.325 kPa) is defined, for example, as 101.325 kPa. As a unit of air pressure, millibars are equal to 100 Pa. (For comparison, one pound per square inch is 6.895 kPa.)

measurement

An ancient unit of length, the hand was standardized at 4 inches (10.16 cm) and is used today primarily to measure the height of horses from the ground to the withers (top of the shoulders). Initially, the width of a palm including the thumb was used as the unit. England's Henry VIII created a statute defining four inches as the width of a hand. A variety of lengths were used by ancient Egyptians, Hebrews, Greeks, and Romans, among others.

apothecaries' weight

An apothecaries' weight is a traditional system of weight in the British Isles used for the measurement and dispensing of pharmaceutical items based on grains, scruples (20 grains), drams (3 scruples), ounces (8 drams), and pounds (12 ounces). The apothecaries' grain is equal to both the troy and avoirdupois grains and represents 1/7,000 of the avoirdupois pound and 1/5,760 of the troy and apothecaries' pounds. The apothecaries' pound is equal to approximately 0.82 avoirdupois pounds, 373.24 grams, and 0.37 kilograms.

The American and British government used apothecaries' weights up until 1858. Great Britain adopted the avoirdupois system for dispensing medicines in that year and switched over to the metric system in 1963 under the authority of the Medical Act. Until 1971, the United States used the apothecaries' weight system until the metric system replaced it.

furlong

English unit of measurement

In the English open- or common-field system, a furlong was measured by the width of an average plowed furrow. 660 feet, or 40 * 4 rod acres, were covered by each furrow. The standardization of linear units such as the yard, foot, and inch began sometime between 1266 and 1303 when the government recognized the traditional sizes of rods, furlongs, and acres as fixed and therefore simply redefined them in terms of the newly standardized units. Therefore, the furlong, commonly measured as 625 feet in northern (German) circles, became 660 feet in standard English circles, and the mile, always eight furlongs in length, became 5,280 feet. The furlong is almost exclusively used in horse racing today.

zhang

ancient unit of measurement

A Wade-Giles chang is an old Chinese measurement of length equal to 10 chi, or 3.58 metres (11 feet 9 inches). China agreed to the value in treaties with England and France (1842–44 and 1858–60). As a result, all tariff duties were assessed using it by Chinese maritime customs. Throughout China, one chi varies in length from 27.9 to 40 cm (11 to 15.8 inches). The so-called treaty chi was defined as 35.8 centimeters (14.1 inches) for customs purposes.

mina

unit of weight

The earliest known

was the mine unit. It was created by the Babylonians and used by the Hittites, Phoenicians, Assyrians, Egyptians, Hebrews, and Greeks. Time and place affected its position and weight relative to its major subdivisions in ancient times. 640 grams (about 23 ounces) of the mine weigh approximately 978 grams (about 34 ounces) in another form.

Ancient Hebrews used the mina, or minah, as a standard of weight. The sacred mine was equal to 60 shekels, and 60 sacred mines were equal to one sacred talent. In the Talmudist system, one Talmudist mine equalled 25 shekels, and 60 Talmudist mines equaled one Talmudist talent. According to some estimates, the Hebrew sacred mine weighs 499 grams (about 18 ounces). The Greek, or Attic, mine, equaled to 100 drachmas, has been estimated at 431 grams.

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rod

measurement

Alternate titles: perch, rd

Related Topics: length unit

Old English rod equals 16.5 feet (5.029 metres), though it varies from 9 to 28 feet (2.743 to 8.534 metres). It was also called a perch or pole. The word rod derives from Old English rodd and is akin to Old Norse rudda (“club”). Etymologically rod is also akin to the Dutch rood which referred to a land area of 40 square rods, equal to one-quarter acre, or 10,890 square feet (1,012 square metres). It also denoted just one square rod, or 272.25 square feet (25.29 square metres). The rood also was a British linear unit, containing 660 feet (201.2 metres).

rod

measurement

rod, old English measure of distance equal to 16.5 feet (5.029 metres), with variations from 9 to 28 feet (2.743 to 8.534 metres) also being used. It was also called a perch or pole. The word rod derives from Old English rodd and is akin to Old Norse rudda (“club”). Etymologically rod is also akin to the Dutch rood which referred to a land area of 40 square rods, equal to one-quarter acre, or 10,890 square feet (1,012 square metres). It also denoted just one square rod, or 272.25 square feet (25.29 square metres). The rood also was a British linear unit, containing 660 feet (201.2 metres).

troy weight

measurement system

Traditional British weight system based on the grain, pennyweight (24 grains), ounce (20 pennyweights), and pound (12 ounces). Since the Middle Ages, troy grains, pennyweights, and ounces have been used to weigh gold, silver, and other precious metals and stones. A major medieval fair was held in the French city of Troyes, hence the name. Troy pounds were adopted by the U.S. Mint to regulate coinage in 1828.

Troy pounds are equal to apothecaries' pounds and to approximately 0.82 avoirdupois pounds and 0.373 kilograms.

astronomical unit

unit of measurement

A unit of length defined as the average, or average distance from Earth to the Sun, defined as 149,597,870.7 km (92,955,807.3 miles). Alternately, it can be regarded as the length of the semimajor axis of Earth's elliptic orbit around the Sun. Astronomical units are convenient units for expressing and relating distances of objects in the solar system and for calculating various astronomical calculations. In order to compare the distances of all three bodies, it may be useful to state that Jupiter is 5.2 AU (5.2 Earth distances) from the Sun, while Pluto is about 40 AU from the Sun.

By using the parallax method, it would have been easiest to determine the astronomical unit value directly. Two observers stationed at the ends of a long, accurate baseline-ideally a baseline the length of Earth's diameter-would simultaneously record the position of the Sun against the essentially motionless background of distant stars. Comparing the observations would reveal an apparent shift, or parallax (angular) displacement, of the Sun against the distant stars. By using this angular value and baseline length, it is possible to determine the Earth-Sun distance by using a simple trigonometric relationship. The method cannot be used in practice, however, because the Sun's glare blots out the background stars needed for the parallax measurement.

Astronomers in the 17th century had a good enough understanding of the geometry of the solar system and the motion of the planets to develop a proportional model of objects in orbit around the Sun, independent of any scale. A precise measurement of the distance between any two objects at a given time was all that was needed to establish the scale for all orbits and determine the astronomical unit. Using the parallax displacement of Mars, Gian Domenico Cassini made a relatively accurate estimate of the astronomical unit in 1672. The distance between Venus and Earth was measured later with observations of Venus transiting the Sun's disk.

During the close approach of Eros to Earth in 1932, the parallax displacement of the asteroid gave what was at the time a very precise value for the astronomical unit. Through a combination of radar ranging of Mercury, Venus, and Mars; laser ranging of the Moon (using light reflectors left by Apollo astronauts on the Moon's surface); and timing of signals returned from spacecraft as they orbit or pass objects in the solar system, astronomers have further refined their knowledge of the dimensions of the solar system and the value of the astronomical unit.

The International Astronomical Union (IAU) defined the astronomical unit as the distance from the Sun at which a massless particle would have a period of one year in a circular orbit. Solar systems were modeled exclusively according to Newtonian principles in this definition. In general relativity, however, such a definition proved impossible since different values of the astronomical unit were obtained depending on an observer's frame of reference. Based on Kepler's third law of planetary motion, the 1976 definition also included the Sun's mass, which is always decreasing since the Sun shines through converting mass into energy. As measurements of the Sun's mass became more precise, the astronomical unit became a time-varying unit. Due to these problems, and the fact that distances in the solar system were known so accurately that the astronomical unit was no longer necessary for a relative scale, the IAU set the astronomical unit at 149,597,870.7 km in 2012.

talent

unit of weight

Many ancient civilizations, including the Hebrews, Egyptians, Greeks, and Romans, used talent as a unit of weight. Over time and location in the ancient world, a talent's weight varied considerably as well as its relationship to its major subdivision, the mine. A ratio of 1:60 was probably the most common for talent to mine.

An ancient Hebrew talent, or kikk*r, probably of Babylonian origin, was their basic unit of weight. In the sacred system of weights, the Talmudic talent was equal to 60 Talmudic minas.