Decimal System is the name given to any system of weights, measures, or money in which the unit is always multiplied by 10 or some power of 10 to give a higher denomination, and divided by 10 or a power of 10 for a lower denomination. This system was originally developed in France, and the principle obtained in the coinage of Belgium, Italy, Spain, Portugal, the United States, and other countries, before eventually spreading to the rest of the world. To express the higher denominations, that is to say, the unit multiplied by 10, 100, 1000, 10,000, the French made use of the prefixes deca, hecto, kilo, myria, derived from the Greek; thus, the metre being the unit of length, decametre is 10 metres, hectometre 100 metres, kilometre 1000 metres. To express lower denominations, that is, tenths, hundredths, etc, the Latin prefixes deci, centi, milli are used in the same way; thus a centilitre is the hundredth part of a litre, decilitre the tenth part of a litre. The basis of the whole system is the linear measure, the unit of which is the metre, which was originally supposed to be the ten-millionth part of a quadrant of the earth's meridian (39.37 inches). The square of 10 metres, or square decametre, called an are, is the unit of surface measure. The cube of the tenth part of the metre or cubic deimetre called a litre is the unit of liquid capacity. The weight of a cubic centimetre of distilled water at 4 degrees centigrade called a gramme is the unit of weight. In Britain the decimal system of weights and measures is known as the metric system. Research Decimal System
The Ocean of Storms (Oceanus Procellarum) is the largest of the dark plains on the surface of the moon. It is situated in the second and third quadrant. Research Ocean of Storms
John Hadley was an English astronomer. He was born towards the end of the seventeenth century and died in 1744. He is the reputed inventor of the quadrant that goes by his name, though the honour is also claimed for Isaac Newton, from whom John Hadley got a description of the instrument in 1727, and for Thomas Godfrey of Philadelphia, who produced his instrument about the same time as John Hadley in 1731. The Royal Society decided that Thomas Godfrey and John Hadley were both entitled to the honour of the invention. John Hadley also invented the sextant. Research John Hadley
An astrolabe is an instrument used to make astronomical measurements, the term is now especially applied to an instrument used for measuring the altitudes of the stars. The Astrolabe was superseded by the quadrant and sextant. The name was also formerly given to an armillary sphere. Research Astrolabe
Horizon-glasses are the two speculums on of the radii of a quadrant or sextant. The one half of the fore horizon-glass is silvered, while the other half is transparent, in order that an object may be seen directly through it. The back horizon-glass is silvered above and below, but has a transparent stripe across the middle, through which the horizon can be seen. Research Horizon-Glasses
Navigation is the science and technology of finding the position, course, and distance travelled by a ship, plane, or other craft. Traditional methods include the magnetic compass and sextant. Today the gyrocompass is usually used, together with highly sophisticated electronic methods, employing beacons of radio signals, such as Decca, Loran, and Omega. Satellite navigation uses satellites that broadcast time and position signals. The Phoenicians, Syrians, Carthaginians, Greeks and Romans conducted their voyages solely by the observation of the heavens, and by keeping as much as possible to the coast. It was not until the voyages made by direction of Prince Henry of Portugal, after 1418, that navigation seems to have been systematically conducted, and the sea-instruments and sea-charts then constructed formed the basis of maritime science until replaced by satellite
navigation equipment in the late 1990s. An early invention that marked progress was the cross-staff, first described by Werner in 1514. It was used for the determination of longitude, by observation of the distance between the moon and some star; and out of it grew the fore-staff and the back-staff.
In 1530 Gemma Frisius of Louvain devised the idea of using small clocks in conjunction with instrumental observation, and the nautical quadrant in some form was thenceforth part of every ship' s furniture. John Davis' quadrant (the back-staff) seems to have been generally preferred for many years. In the early 16th century there also cam into use at sea the astrolabe, for taking the altitude of the sun and stars. This instrument was made very heavy, so that it hung perpendicularly and steadily. The middle of the 16th century saw the invention of the log-line. Voyages were, however, conducted rather by guesswork and experience, and especially so previous to the discovery of methods of finding the longitude. Mercator's system of plane charts furthered
progress; and Edward Wright discovered the true method of dividing the meridian, and drew up a table for the use of navigators by which latitude could be determined.
The US global positioning system (GPS) was introduced 1992 and features 24 Navstar satellites that enable users to triangulate their position (from any three satellites) to within 15 m. In 1992, 85 nations agreed to take part in trials of a new navigation system which makes use of surplus military space technology left over from the Cold War. The new system, known as FANS or Future Navigation System, makes use of the 24 Russian Glonass satellites and the 24 US GPS satellites. Small computers will gradually be fitted to civil aircraft to process the signals from the satellite, allowing aircraft to navigate with pinpoint accuracy anywhere in the world. The signals from at least three satellites will guide the craft to within a few metres of accuracy. FANS will be used in conjunction with four Inmarsat satellites to provide worldwide communications between pilots and air-traffic controllers.
An Australian prototype for an electronic navigation system ECDIS (Electronic Chart Display Information System) is a single computer-based apparatus that combines information from existing navigational aids, such as charts, radar, sonar and satellites. Research Navigation
The quadrant was probably the earliest astronomical instrument to be used at sea. It consists of a flat plate in the shape of a quarter-circle, with a plumb-line suspended from the apex. The hand- held quadrant is held in a vertical plane with the right angle away from the eye and the curved edge downwards. One of the straight edges is equipped with a pair of metal pinhole sights which are aligned with an astronomical object and the hanging cord reads off the altitude of this object above the horizon on the circular scale. It was used in the 15th century to measure the altitude of a celestial body, usually the pole star. The English quadrant or back-staff, first described in 1595, was a more complex instrument that measured the altitude of the Sun by the shadow the
quadrant cast. The back-staff was more accurate than previous instruments, and had the advantage that the observer had his back to the Sun. It generally superseded the old
quadrant, the astrolabe, and the cross-staff in the 17th century. A larger form of quadrant, known as a mural quadrant, is mounted on a north-south wall and has a solid arm instead of a hanging cord. This obsolete instrument was superseded by the meridian, or transit, circle, a telescope free to move only in the meridian or north-south plane. Research Quadrant
HMAS Quadrant was a British-built Australian Queensborough Class destroyer of 1705 tons displacement launched in 1942 and lent to the Royal Australian Navy in 1945. HMAS Quadrant was powered by two Admiralty 3-drum type boilers and carried a complement of 220. She was armed with four 4.7 inch guns; four 2 pdr guns; two 40 mm anti-aircraft guns; 20 mm anti-aircraft guns and eight 21 inch torpedo tubes. Research Quadrant
The Probert Encyclopaedia was designed, edited and programed by
Matt and Leela Probert
Abbreviations
Research Decimal System
