Medieval Navigation Tools
At the time the Arabella and the Talbot departed Southampton Harbour, the astrolabe was still the most important navigation device employed by Medieval navigators. [We described its use in great detail in Crossing the Ocean Sea.]
Two astrolabes from the 1600s displayed in the British Maritime Museum [fronts and backs].
The Spanish cosmologist Abraham Zacuto and the Nuremberg scientist Martin Behaim improved the ancient Egyptian tool during the 1480s so that it was useful for navigation south of the equator where the Pole Star [aka North Star or Polaris] was no longer visible. Vasco da Gama could not have found his way to India in 1498 without it.
Most of the other tools we described earlier were still in use:
- The sun dial and the hourglass for telling time
- The magnetic compass for finding direction
- The sounding lead to measure the depth of the sea floor and its condition
- The chip-reel for determining speed
New to English navigation in 1540 was the cross-staff, introduced at that time by John Dee (1527-1608/9). He had learned about the device for measuring the angle of the celestial bodies in relation to the horizon when he studied with famous cartographers and navigators in the Netherlands. [More about John Dee later.]
As we also discussed in Crossing the Ocean Sea, the trouble with the cross staff was that it required the navigator, when using it during the daytime, to look directly at the sun. In around 1594, English inventor and explorer John Davis came up with a solution to that problem: the back-staff or Davis Quadrant. Davis’ device consisted of two arcs of a circle that measured up to 90 degrees, hence the name quadrant, or quarter of a circle. Each arc had a sliding vane with two alignment peep-holes. The navigator stood with his back to the sun while he lined up the shadows on the vanes.
But the backstaff was not as accurate as the cross-staff. The Dutch East India Company, which was active after 1600, prohibited its use by its company’s navigators.
John Davis’ Backstaff Quadrant, 1594.(1)
Quadrants from the early 1600s on display at the British Maritime Museum, London.
A graphometer designed by Paris scientist Philip Danfrie around 1600, on display in the British Maritime Museum.
According to the placard in the British Maritime Museum where this graphometer is displayed, the instruments were “used in surveying to find the angular distance between two landmarks.” The instrument was mounted on a staff and orientated north-south with the help of the small compass at its center.
An Italian Nocturnal made in Rome in 1589 on display at the British Maritime Museum
This nocturnal, also on display in the British Maritime Museum, allowed a navigator to tell time from the stars around the Pole Star, “normally those in the constellations of the Great Bear [Big Dipper] and the Little Bear [Little Dipper].” “Nocturnals were mainly used between the fifteenth and seventeenth centuries. English examples tended to be made of boxwood, while metal ones like this were more common in mainland Europe.”
Next article: Direction by the Names of the Winds
- Photo by Mcapdevila. Attribution: Own work, CC BY-SA 3.0. Image source: https://commons.wikimedia.org/w/index.php?curid=16132602