Marine sandglass
Encyclopedia
Marine sandglass, is an ancient marine instrument employed to measure (or rather estimate) the time at sea when used as a 30 minute hourglass
. It was also used together with the chip log
, to measure the boat speed through the water in knots (in this case with a 3 minute glass or less).
Originally, it consisted of two glass bottles one above the other with both ends connected by a tube. Over time, the progress of glassblowing allowed it to be made in one single piece.
The Marine glass was filled with sand or a suitable material such as finely ground lead or tin chips (used to avoid humidity). 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 (which could be calibrated). Once the upper "glass" was empty, the glass could be "turned" to measure another time period.
Although its use was vital to cross the oceans, the Marine glass was not such an accurate instrument to measure the passage of time. Many factors could affect the duration of sand's flow: the humidity inside the "glass", the uniformity in fineness of the sand, the inner diameter of the connecting tube with a possible wear caused by the flow of sand, the more or less horizontal position, the effect of acceleration or deceleration of the ship's movements, all could influence the flow of sand and hence the time measured.
The earliest recorded reference, which can be said with certainty to refer to a marine-glass, is dated 1345/46. It's contained in the Receipt of Thomas de Stetesham, Clerk of the King's Ship called "La George" within the reign of Edward III, which translated from Latin says:
"The same Thomas accounts has paid at Lescluse (Sluys) in Flanders for xii horologes of glass( pro xii orlogiis vitreis) a price of 4 1/2 'gross' each, in sterling 9s.
Item, for iv horologes of the same type (de eadem secta), a price of five 'gross' each, making in sterling 3s. 4d."
The next reference is found in an inventory of effects of Charles V of France, which were in his possession at his death on September, 16, 1380. It's an inventory of about four thousand items and one of them describes an hour-glass in the king's study at his castle of St. Germain en Laye in the following terms.
"Item ung grant orloge de mer, de deux grans fiolles plains de sablon, en ung grant estuy de boys garny d'archal."
("Item a large sea clock, with two large phials filled with sand, in a large wooden brass-bound case.)
The most interesting thing about the second reference is that a common sand-glass is defined as a "sea clock", which suggests that, at this period, the sand-glass was more commonly used at sea and may have its origins in a maritime need..
", permitted the navigator to plot his position on a map. Multiplying the velocity by the time (measured with the glass) the course had been kept, gave the traveled distance, with the compass showing the sailing direction. This is the simple method called dead reckoning
(an abbreviation for estimated calculation).
Until the beginning of the 19th century, when it was possible to navigate by the lunar distances, dead reckoning navigation periodically contrasted with the measurement of latitude taken with the quadrant,(backstaff
, astrolabe
, octant
), was the only system available to mariners to navigate the globe. That's the reason why the "Marine sandglass" was so important for sailors. At the same time, "on the mainland" mechanical clocks were used (apart from the sundials and hourglasses) to know the time, and this parallel situation lasted more than four hundred years from 1350 to 1805.
Columbus, on his ships, logged the pass of time by a half-hour "ampolleta" (glass) that was turned every time it emptied, to keep track of the "canonical" hours.
During the voyage of Ferdinand Magellan
around the world, he equipped every ship with 18 hourglasses . It was the job of a ship's page to turn the hourglass, thus supplying the time to be registered on the ship's log. Noon was the reference time for navigation, not dependent on the glass as the Sun would be in its zenith
.. A variable number of hourglasses were sometimes fixed in a common frame, each with a different operating time, for example, 1 hour, 45 minutes, 30 minutes and 15 minutes.
, to measure the speed (in knots) of the vessel over the water. The procedure was as follows:
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 "Five knots and fourth!
Hourglass
An hourglass measures the passage of a few minutes or an hour of time. It has two connected vertical glass bulbs allowing a regulated trickle of material from the top to the bottom. Once the top bulb is empty, it can be inverted to begin timing again. The name hourglass comes from historically...
. It was also used together with the chip log
Chip log
A chip log, also called common log, ship log or just log, is a navigation tool used by mariners to estimate the speed of a vessel through water.-Construction:...
, to measure the boat speed through the water in knots (in this case with a 3 minute glass or less).
Originally, it consisted of two glass bottles one above the other with both ends connected by a tube. Over time, the progress of glassblowing allowed it to be made in one single piece.
The Marine glass was filled with sand or a suitable material such as finely ground lead or tin chips (used to avoid humidity). 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 (which could be calibrated). Once the upper "glass" was empty, the glass could be "turned" to measure another time period.
Although its use was vital to cross the oceans, the Marine glass was not such an accurate instrument to measure the passage of time. Many factors could affect the duration of sand's flow: the humidity inside the "glass", the uniformity in fineness of the sand, the inner diameter of the connecting tube with a possible wear caused by the flow of sand, the more or less horizontal position, the effect of acceleration or deceleration of the ship's movements, all could influence the flow of sand and hence the time measured.
History
Although no one knows exactly when it was first used on the seas for navigational purposes, the use of the Marine sandglass has been recorded since the 14th centuryThe earliest recorded reference, which can be said with certainty to refer to a marine-glass, is dated 1345/46. It's contained in the Receipt of Thomas de Stetesham, Clerk of the King's Ship called "La George" within the reign of Edward III, which translated from Latin says:
"The same Thomas accounts has paid at Lescluse (Sluys) in Flanders for xii horologes of glass( pro xii orlogiis vitreis) a price of 4 1/2 'gross' each, in sterling 9s.
Item, for iv horologes of the same type (de eadem secta), a price of five 'gross' each, making in sterling 3s. 4d."
The next reference is found in an inventory of effects of Charles V of France, which were in his possession at his death on September, 16, 1380. It's an inventory of about four thousand items and one of them describes an hour-glass in the king's study at his castle of St. Germain en Laye in the following terms.
"Item ung grant orloge de mer, de deux grans fiolles plains de sablon, en ung grant estuy de boys garny d'archal."
("Item a large sea clock, with two large phials filled with sand, in a large wooden brass-bound case.)
The most interesting thing about the second reference is that a common sand-glass is defined as a "sea clock", which suggests that, at this period, the sand-glass was more commonly used at sea and may have its origins in a maritime need..
Importance of the "Marine sandglass" in navigation
In long-distance navigation through the open ocean, the "glass" to measure the time was a tool as important as the compass for the course. Filled with the amount of sand suitable for measuring a lapse of half an hour, each time the sand emptied was called a "glass" and eight "glasses" (four hours), defined a "watch". The compass and the "sandglass", along with the record in the logbook, of the speed measured with the "chip logChip log
A chip log, also called common log, ship log or just log, is a navigation tool used by mariners to estimate the speed of a vessel through water.-Construction:...
", permitted the navigator to plot his position on a map. Multiplying the velocity by the time (measured with the glass) the course had been kept, gave the traveled distance, with the compass showing the sailing direction. This is the simple method called dead reckoning
Dead reckoning
In navigation, dead reckoning is the process of calculating one's current position by using a previously determined position, or fix, and advancing that position based upon known or estimated speeds over elapsed time, and course...
(an abbreviation for estimated calculation).
Until the beginning of the 19th century, when it was possible to navigate by the lunar distances, dead reckoning navigation periodically contrasted with the measurement of latitude taken with the quadrant,(backstaff
Backstaff
The backstaff or back-quadrant is a navigational instrument that was used to measure the altitude of a celestial body, in particular the sun or moon...
, astrolabe
Astrolabe
An astrolabe is an elaborate inclinometer, historically used by astronomers, navigators, and astrologers. Its many uses include locating and predicting the positions of the Sun, Moon, planets, and stars, determining local time given local latitude and longitude, surveying, triangulation, and to...
, octant
Octant (instrument)
The octant, also called reflecting quadrant, is a measuring instrument used primarily in navigation. It is a type of reflecting instrument.-Etymology:...
), was the only system available to mariners to navigate the globe. That's the reason why the "Marine sandglass" was so important for sailors. At the same time, "on the mainland" mechanical clocks were used (apart from the sundials and hourglasses) to know the time, and this parallel situation lasted more than four hundred years from 1350 to 1805.
Watch sandglass
Was used on ships to measure half-hour periods. The helmsman was responsible for turning it upside down. It began with the midday's sun, knocking the bell once, after half an hour twice, and so on .. But if a sailor wanted to shorten his guard, he only needed to turn the glass before it had fully emptied.Columbus, on his ships, logged the pass of time by a half-hour "ampolleta" (glass) that was turned every time it emptied, to keep track of the "canonical" hours.
During the voyage of Ferdinand Magellan
Ferdinand Magellan
Ferdinand Magellan was a Portuguese explorer. He was born in Sabrosa, in northern Portugal, and served King Charles I of Spain in search of a westward route to the "Spice Islands" ....
around the world, he equipped every ship with 18 hourglasses . It was the job of a ship's page to turn the hourglass, thus supplying the time to be registered on the ship's log. Noon was the reference time for navigation, not dependent on the glass as the Sun would be in its zenith
Zenith
The zenith is an imaginary point directly "above" a particular location, on the imaginary celestial sphere. "Above" means in the vertical direction opposite to the apparent gravitational force at that location. The opposite direction, i.e...
.. A variable number of hourglasses were sometimes fixed in a common frame, each with a different operating time, for example, 1 hour, 45 minutes, 30 minutes and 15 minutes.
Ship-log sandglass
From the 16th century a smaller "glass" was used along with the chip logChip log
A chip log, also called common log, ship log or just log, is a navigation tool used by mariners to estimate the speed of a vessel through water.-Construction:...
, to measure the speed (in knots) of the vessel over the water. The procedure was as follows:
A sailor ran the chip log
Chip log
A chip log, also called common log, ship log or just log, is a navigation tool used by mariners to estimate the speed of a vessel through water.-Construction:...
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 "Five knots and fourth!