For centuries, superstition and religious dread had dictated that the world was flat and the sea populated by horrendous monsters - mariners would sail over the edge of the world or have their ships torn apart by demonic creatures.
The resurrection of Ptolemies works brought back the idea that the earth was round, and introduced the use of latitude and longitude.
The Compass
- The earliest compass was a magnetized needle floating in a bowl of water. Some scholars believe that the compass only really gained popularity amongst mariners at the dawn of the age of discovery. Early compasses consisted of a needle attached to a wind rose (the drawing indicating all the points of the compass), protected by a glass cover and fixed into a box aligned with the keel of the ship. As ships ventured further and further into unknown waters, and ocean voyages increased in duration, the compass was invaluable.
Finding out where one actually sat on the vastness of the planet proved difficult. To begin with, measuring latitude - the distance north or south of the equator - was relatively simple. But the measurement of longitude - east to west - was another matter entirely, and relied upon accurate time-keeping devices and the establishment of the Greenwich line as the Prime Meridian. These weren't around in the early period of the age of discovery. Devices for measuring time and latitude included:
The Quadrant
- A quadrant is a piece of metal, shaped, as it's name implies, like one-quarter of a circle. It was used to measure the altitude of heavenly bodies. The outer rim was marked in degrees, from 0 - 90. At the apex of the quarter, a length of weighted string was fastened. The user aligned the quadrant on star or sun by sighting along the top edge and allowing the string to swing freely across the scale of degrees. From this, the altitude of whatever the user was sighting at could be calculated, and by consulting lists of tables, a mariner could then determine his latitude (distance north or south of the equator). The quadrant evolved from the astrolabe.
The Astrolabe
- Astrolabes had been in use for centuries. Basically, the astrolabe was a disc of brass marked on the outer edge with graduations of degrees. Through the centre of the disc, a pin held a rotating vane known as an alidade. The user held the astrolabe vertically through a ring at the top and pointed the plane (edge) at the object he was sighting on. He then aligned the alidade on the object and checked the altitude in degrees against the outer rim of the astrolabe.
The Cross Staff
- The cross staff or Jacobs staff was a bulky instrument consisting of a long main staff, marked with graduations, and a sliding transverse, or transom staff - hence its name. One end of the staff was placed against the users cheek and the lower end of the transversal would be aligned on the horizon. The user would then align the top end of the transversal against sun or stars and check the alignment, and hence, the altitude, on the degrees inscribed on the mainstaff. The cross staff was cumbersome and difficult to use.
The Dipping Needle
- Dipping needles were used when the weather didn't permit celestial observation. They were strips of magnetised iron placed on a pin so that they swung freely up or down. The north tip of the needle pointed down when the vessel was south of the magnetic equator - and the south tip pointed up when the ship was in the northern hemisphere. In essence, a vertical compass.
It wasn't until the late 1700's that the puzzle of longitude was eventually solved. Yorkshireman John Harrison invented a special marine chronometer, a clock that could keep it's time despite the rigours of temperature, humidity and movement.
A navigator then knew the exact time at the Greenwich Observatory in London ( the Greenwich Meridian). By measuring the sun or stars, he could determine the time at the place where he sat: a calculation involving tables and the two times gave him his longitude.
Sources:
To the Ends of The Earth Journeys of the Great Explorers, Jon Balchin, Arcturus Publishing Ltd, 2006
