Marine sandglass

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.

[1] 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.

The marine glass was filled with sand or a suitable material such as finely ground eggshell, lead or tin chips (used to avoid humidity).

[2] The origin of the hourglass is unclear, although unlike its predecessor the clepsydra, or water clock, which may have been invented in ancient Egypt, the first referenced use: From the Roman time it disappears completely from historical records until it is re-introduced in medieval Europe.

[9][10] 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.

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:[15][16] The same Thomas accounts to have paid at Lescluse, in Flanders, for twelve glass horologes (" pro xii.

In the shipment, John asks his daughter to send him the manuscript by Jean de Mandeville, "to translate it into the Aragonese language".

[20][21][22] 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).

[2][3] 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.

[2][3] Multiplying the ship's speed by the time the course had been kept (measured with the glass), gave traveled distance,[2][3] a simple, overall method termed dead reckoning.

[2][3] 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.[25]

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!"