3-2-29a-1 Antikythera

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3-2-29a-2 Mechanical Age Navigational Instruments

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Introduction

0 Background
1 Italian Compass 1570
2 Octant 1760
3 Persian Astrolabe 1660 Persian Astrolabe 1660
4 Spanish/Portuguese Astrolabe 1588 Spanish/Portuguese Astrolabe 1588
5 Cross Staff 1770 Cross Staff circa 1700
6 Mariner's Quadrant 1720/25
7 Old English Compass 1750
8 Old German Compass
9 Gigantic Astronomical Sextant

Introduction 

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The first records of boats large enough to carry trading goods are from between 3500 BC to 3000 BC, so we can safely assume that that time also marked the beginning of navigation. These first navigators had no choice but stay close to shore and navigate by sight of landmarks or other characteristics on land that they could see. They travelled mostly by day and went for a safe harbor to stay at anchor at night. They did however develop kind of rudimentary charts, which listed directions, showed crude drawings depicting landmarks and certain dangerous places like reefs, sandbanks or rocks in the water. Early documents state that the more experienced mariners of the time were said to plot their course by using certain star constellations so most vessels followed the east/west movement of the sun or the track of the stars.

 Background

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However, the ancient navigator had no way to accurately determine longitude and therefore, once out of sight of land, had no idea how far east or west he was. So his estimates were made based upon the time it took to sail from A to B. This is the simplest form of navigation and it is called dead-reckoning; it is still used by navigators today. To determine the distance travelled from one point to another, the navigator would multiply the time he sailed by the speed of the vessel. Of course these crude calculations were often way off because time was still measured with a sandglass and speed was estimated by watching pieces of seaweed or wood pass by the hull.

 Italian Compass 1570

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Italian Compass 1570 - The inner bowl with the compass face is mounted in a brass gimbal ring to reduce the effects of the ship's motion at sea. The soft iron needle is diamond-shaped and is fixed to the underside of the vellum and paper card. The compass face is divided into thirty-two points. Decorations on the north and east points were quite common up to the 19th century, wherby east for Europeans has been the direction of the Holy Land. Most early compasses were set in wooden bowls or boxes.

 Octant 1760

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Octant 1760 - The octant, also known as Hadley's quadrant, forms an eighth of a circle but the use of reflection doubles the angle, so that the scale reads up to 90 degrees. It has a radius of 17.75 inches (45.1 cm). Sir Isaac Newton developed the principle of the octant but is was not until 1731 when John Hadley demonstrated its use for marine purposes to the Royal Society in London. The use of mirrors to bring a reflected image of stars or the sun alongside the horizon, when viewed through the sight improved the accuracy of navigation considerably. This octant has been crafted by Benjamin Martin, London, circa 1760.

 Persian Astrolabe 1660 Persian Astrolabe 1660

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Persian Astrolabe 1660 Persian Astrolabe 1660 - The astrolabe represents a mathematical likeness of the heavens and its Greek name is - "Star Taker". This amazing sophisticated scientific instrument has been crafted by Muhammad Mahdi al-Khadim al-Yazdi in brass and was used to solve astronomical problems and to show the positions of stars and planets at different dates, times and latitudes. The Persian calligraphy engraving reads a quotation from the Koran: "The world is decorated with stars".

 Spanish/Portuguese Astrolabe 1588 Spanish/Portuguese Astrolabe 1588

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Spanish/Portuguese Astrolabe 1588 Spanish/Portuguese Astrolabe 1588 - The mariner's astrolabe has been developed by Arabic astronomers. Christopho Columbo used a similar astrolab design on his voyages to discover the "New World". It was a simplified version of an instrument for measuring the height of stars and the sun above the horizon level. This astrolabe has been discovered in southern Ireland were several ships of the Spanish Armada foundered.

 Cross Staff 1770 Cross Staff circa 1700

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Cross Staff 1770 Cross Staff circa 1700 - This particular Cross-Staff has been crafted by Thomas Tuttell, London, circa 1700. The cross-staff was another instrument designed to measure the altitude of the sun or polar star. It made use of the properties of right-angled triangles, or trigonometry. The navigator or captain rested the main staff just below his eye and moved the cross until the bottom was aligned with the horizon level, and the top with the lower edge of star or sun. The position could then be read off on the scale in degrees and minutes. Cross-staves were mostly made of wood, but there are indications that some have been crafted in metall (brass) as well. Constantly looking at the sun with an instrument of this kind has often caused blindness.

 Mariner's Quadrant 1720/25

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Mariner's Quadrant 1720/25 - The mariner's quadrant was one of the earliest devices developed for measuring angles, either of a star above the horizon level or the top of a hill in surveying. The name suggests, it consists of a quarter of a circle, with the curved edge divided into 90 degrees, a cord with an attached weight suspended from the point of the right-angle. The object was aligned through the sights on one edge, and the angle of elevation read off where the cord crossed the scale. This instrument is made of brass and its degree scale is subdivided for measurements to 30 minutes of arc.

 Old English Compass 1750

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Old English Compass 1750

 

 Old German Compass

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Old German Compass

 

 Gigantic Astronomical Sextant

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Gigantic Astronomical Sextant

Gigantic Astronomical Sextant - Astronomical sextants had been in use since the 16th century.


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