A marine sandglass is a timepiece of simple design that is a relative of the common hourglass, a marine (nautical) instrument known since the 14th century (although reasonably presumed to be of very ancient use and origin). They were employed to measure the time at sea or on a given navigational course, in repeated measures of small time increments (e.g., 30 minutes). Used together with the chip log, smaller marine sandglasses were also used to measure the boat speed through the water in knots.
Although vital to maritime navigation, marine sandglasses were not accurate measuring instruments for the passage of time; many design and environmental factors could affect the duration of sand's flow, and therefore its reported time. Their use continued through the early 19th century, when they were supplanted by reliable mechanical timepieces, and by other advances in marine navigation.
Marine sandglasses were very popular on board ships, as they were the most dependable measurement of time while at sea. Unlike the clepsydra, the motion of the ship while sailing did not affect the hourglass. The fact that the hourglass also used granular materials instead of liquids gave it more accurate measurements, as the clepsydra was prone to get condensation inside it during temperature changes. In conjunction with a record of a ship's speed and direction, seamen used the hourglass to determine their position with reasonable accuracy.
Marine sandglasses originally consisted of two glass bottles one inverted above the other, connected by a small tube, with the ends wrapped and so joined together. Over time, the later progress in the art of glassblowing allowed them to be made in a single piece. The marine glass was filled with sand or a suitable material such as finely ground eggshell, lead or tin chips (used to avoid humidity). This flowing material was chosen with two main objectives: to avoid the humidity and to absorb motion, both required for shipboard use.
Placed in the upper half, the sand would flow slowly and steadily towards the lower half by the action of gravity, taking a certain time to empty (that was calibrated during their design and manufacture). Once the upper portion of the glass was empty, the glass could be turned to measure another time period.
From the Roman time it disappears completely from historical records until it is re-introduced in medieval Europe. By the 8th century it is mentioned by a monk named Luitprand, who served at the cathedral of Chartres, France. But it was not until the 14th century that the marine sandglass was seen commonly, the earliest firm evidence being a depiction in the 1338 fresco Allegory of Good Government by Ambrogio Lorenzetti.
Use of the marine sandglass has been recorded since the 14th century; The written records about it were mostly from logbooks of European ships. In the same period it appears in other records and lists of ships stores. The earliest recorded reference that can be said with certainty to refer to a marine sandglass dates from c. 1345, in a receipt of Thomas de Stetesham, clerk of the King's ship La George, in the reign of Edward III of England; translated from the Latin, the receipt says: in 1345:
The same Thomas accounts to have paid at Lescluse, in Flanders, for twelve glass horologes (" pro xii. orlogiis vitreis "), price of each 4½ gross', in sterling 9s. Item, For four horologes of the same sort (" de eadem secta "), bought there, price of each five gross', making in sterling 3s. 4d.
Another reference is found in an extensive inventory of the property of Charles V of France in his possession at the time of his death on September 16, 1380. One item is an hourglass from the king's study at his castle of St. Germain en Laye, described as follows:
This "orloge de mer" or "heures de naviguer" was sent to him, as a present, when he still was a prince (being therefore prior to 1356 when he took the place of his imprisoned father), by his aunt Yolande of Aragon, when asking him for a manuscript of John de Mandeville, to be translated to the Aragonese tongue.
The most interesting thing about the second reference, the one from King Charles, is that a common sand-glass is defined as "ung grant orloge de mer" or "a large sea clock", this together with the fact that the first explanation of its use at sea (found by M.Llauradó) appears in the Francesc Eiximenis work "lo dotzé del crestià" and that was given to him as a present by his aunt Yolande of Aragon, suggests that, at this period, the importance of a sand-glass was more commonly related to its use at sea and its fabrication demand may have been originated from the navigational needs from the Crown of Aragon a maritime power of the moment in the Mediterranean.
In long-distance navigation through the open ocean, the sandglass or "glass" used to measure the time was a tool as important as the compass (which indicated sailing direction, and so ship's course). Filled with the amount of sand suitable for measuring a lapse of half an hour, each time the sand emptied was also called a "glass"; eight glasses (four hours) defined a "watch". The times determined by the sandglass, along with the record in the logbook of the speed measured with the "chip log", permitted the ship's navigator to plot his map position. Multiplying the ship's speed by the time the course had been kept (measured with the glass), gave traveled distance, a simple, overall method termed dead reckoning.
The marine sandglass was critical for maritime navigation before the 19th century. At the beginning of that century it became possible to navigate by the lunar distances, thanks to the tables of haversines of Joseph de Mendoza y Ríos. Prior to this, dead reckoning navigation based on sandglass-determined times was used, alongside determination of latitude using the quadrant (see also backstaff, astrolabe, and octant); this was the only system available to mariners to navigate the globe. The parallel use of relative time measurements at sea, and time measurement by mechanical clocks on land continued from at least 1350 to 1805, i.e., for more than 450 years.
Although vital to navigation, the marine glass was not an accurate instrument to measure the passage of time. The design of the glass affected its accuracy in time measurement; the uniformity in fineness of the sand, the inner diameter of the connecting tube, and design aspects allowing wear that would effect the flow of sand all could contribute. In addition, many shipboard factors could affect the duration of sand's flow and therefore influence the time measured, including the humidity inside the glass, the ability for it to be positioned in a perfectly vertical position, and the acceleration or deceleration of the ship's movements. Finally, the use of short duration glasses to measure long periods of time introduced further error. Marine glass use was supplanted by reliable mechanical timepieces, and by other advances in marine navigation.
Watch sandglasses were used on ships to measure watch times, typically in half-hour periods. The helmsman or ship's page were the crewmen responsible for turning the watch sandglass, thus supplying the time to be registered on the ship's log; watch measurement began with the sun reaching its highest point—its zenith—at midday, which was likewise the essential time reference point for navigation. At that point in time, the ship's bell was struck eight times; after the first glass had emptied (half an hour), the ship's bell was struck once, after another glass, twice, and so on until four hours after midday, when it was again struck eight times. At that point, a new watch began, and the sequence was repeated.
Hence, in the voyages of Columbus, there are records that his crew logged the passage of time using a half-hour "ampolleta" (glass) that was turned every time it emptied to keep track of the "canonical" hours. Likewise, during the voyage of Ferdinand Magellan to circumnavigate the globe, 18 hourglasses from Barcelona were in the ship's inventory, after the trip being authorized by emperor Charles V.
A sailor ran the chip log and another sailor the sandglass. The slide of the pulled over the stern and let run the first length of line till the quadrant was stabilized in the water. The sailor was leaving to run the line to pass freely leaving the slide by hand and touching the first knot sang "mark!" At the moment of the inverted glass and time began to run while the line was counting the knots as they passed until the sandglass sang "mark!" a second blow when they had dropped all the sand, then he caught the firmly the line, measuring the fraction of knot elapsed to the last mark! and cried P.E.: "Five knots and four fathoms!..
Great-circle navigation or orthodromic navigation (related to orthodromic course; from the Greek ορθóς, right angle, and δρóμος, path) is the practice of navigating a vessel (a ship or aircraft) along a great circle. Such routes yield the shortest distance between two points on the globe.Grid compass
A grid compass known as well as grid steering compass, is a navigating instrument. It is a design of magnetic compass that facilitates steering a steady course without the risk of parallax error.
The grid compass is the simplest steering compass from the pilot's or helmsman's point of view, because he doesn't need to watch the number (or the division mark) of the wanted course. He has only to steer the craft so that the N/S compass needle lies parallel between the lines of the overlay disc. The principle is similar to the compass-controlled autopilot. Although sophisticated electronics have taken over for commercial navigation, light aircraft, gliders and yachtsmen still use the grid compass because of its simplicity and ease of use.Hourglass
An hourglass (or sandglass, sand timer, sand clock or egg timer) is a device used to measure the passage of time. It comprises two glass bulbs connected vertically by a narrow neck that allows a regulated trickle of material (historically sand) from the upper bulb to the lower one. Factors affecting the time it measured include sand quantity, sand coarseness, bulb size, and neck width. Hourglasses may be reused indefinitely by inverting the bulbs once the upper bulb is empty. Depictions of hourglasses in art survive in large numbers from antiquity to the present day, as a symbol for the passage of time. These were especially common sculpted as epitaphs on tombstones or other monuments, also in the form of the winged hourglass, a literal depiction of the well-known Latin epitaph tempus fugit ("time flies").Josef de Mendoza y Ríos
Josef (also José or Joseph) de Mendoza y Ríos (1761–1816) was a Spanish astronomer and mathematician of the 18th century, famous for his work on navigation.
The first work of Mendoza y Ríos was published in 1787: his treatise about the science and technique of navigation in two tomes. He also published several tables for facilitating the calculations of nautical astronomy and useful in navigation to calculate the latitude of a ship at sea from two altitudes of the sun, and the longitude from the distances of the moon from a celestial body.
In the field of the nautical instruments, he improved the reflecting circle.In 1816, he was elected a foreign member of the Royal Swedish Academy of Sciences.La Cartografía Mallorquina
La Cartografía Mallorquina ( The Majorcan cartography ) is a book of essays on the Majorcan portolans written by Professor Julio Rey Pastor with the collaboration of Ernesto García Camarero. It is a scholarly essay, a key element in the study of portolans, especially those made by Majorcans as half of the book is devoted to the study of more than 400 Majorcan portolans existing worldwide.Loxodromic navigation
Loxodromic navigation (from Greek λοξóς, oblique, and δρóμος, path) is a method of navigation by following a rhumb line, a curve on the surface of the Earth that follows the same angle at the intersection with each meridian. This serves to maintain a steady course in sailing.
Navigating on a spherical surface with a fixed course ( in the figure) results in a spiral path that approaches the North Pole for courses ranging from 270º to 090º and the South Pole for courses from 090º to 270º. On a nautical chart plotted according to the Mercator projection, a loxodromic course appears as a straight line.Rhumbline network
A rhumbline network, or more properly called, a windrose network, is a navigational aid drawn on portolan charts. This network is like a web (see picture) forming a grid on the map. The grid can be easily spotted (as parchment is quite translucent) by observing the map from its rear face, with a light source illuminating the other side. The hole in the center of the circle, origin of the whole network, is also clearly visible from the rear.The lines are not true rhumb lines in the modern sense (reason to put the title in italics), since these can only be drawn on modern map projections and not on 13th century charts. They were close to true rhumb lines in the Mediterranean area but highly inaccurate in the Teixeira planisphere and the other planispheres drawn in any pre-Mercator projection.Sandglass
A sandglass is a device for measuring time, including:
Egg timerIt can also refer to:
Sandglass (TV series), a 1995 Korean drama seriesTerm (time)
A term is a period of duration, time or occurrence, in relation to an event. To differentiate an interval or duration, common phrases are used to distinguish the observance of length are near-term or short-term, medium-term or mid-term and long-term.
It is also used as part of a calendar year, especially one of the three parts of an academic term and working year in the United Kingdom: Michaelmas term, Hilary term / Lent term or Trinity term / Easter term, the equivalent to the American semester. In America there is a midterm election held in the middle of the four-year presidential term, there are also academic midterm exams.
In economics, it is the period required for economic agents to reallocate resources, and generally reestablish equilibrium. The actual length of this period, usually numbered in years or decades, varies widely depending on circumstantial context. During the long term, all factors are variable.
In finance or financial operations of borrowing and investing, what is considered long-term is usually above 3 years, with medium-term usually between 1 and 3 years and short-term usually under 1 year. It is also used in some countries to indicate a fixed term investment such as a term deposit.
In law, the term of a contract is the duration for which it is to remain in effect (not to be confused with the meaning of "term" that denotes any provision of a contract). A fixed-term contract is one concluded for a pre-defined time, although it may also include provision for it to be extended. A contractor required to deliver against a term contract is often referred to as a "term contractor".
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