© Duane A. Cline 1999
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Navigation: The Mariner's Quadrant The quadrant is a very simple instrument of medieval origin used to determine the altitude of a heavenly body. It takes it
name from its shape, which is a quarter of a circle. The curved edge is divided from 0 to 90 degrees. At the apex is a right
angle, where a cord with a small weight, or plumb-bob, of lead or brass is attached. Along one straight edge are mounted
two upright pieces with holes for sighting. When in use, the quadrant is held vertically so the plumb-line falls across the
scale of degree markings, and from this the angle of elevation can be read. There were several types of quadrants in use from an early time: The Islamic quadrant had an astrolabe quadrant on one
side; the gunner's quadrant was a simple sighting device used by artillery officers; the astronomers quadrant was engraved
with geometrical and square lines showing the sun's path through signs of the zodiac. Although the simple mariner's quadrant was in use long before its first mention in 1450, it does not appear the English
sailors adopted its use to any degree. We mention it here simply because it is one of the instruments Capt. John Smith
thought should be aboard any ship making an extended voyage such as Mayflower. The average seam of the day would not have much use for the complicated quadrants used by astronomers. Therefore, a
much simpler form of quadrant for taking altitudes was adopted by those mariners who opted to use it for observation at
see. The mariner's quadrant was cut from a piece of metal plate - sometimes wood. It radius was about 6-8 inches. It had a pair
of rectangular plates with pinhole sights on one of the straight edges for sighting. The only scale needed was the degree
marks on the curved edge. It was light and easy to handle. The following illustration can be used as a coloring page for the students' notebooks. It could also be transferred to a piece
of cardboard and cut out if the student wishes to make a reproduction. Materials needed for a reproduction: 1. Heavy cardboard 2. A protractor for setting the degree-markings 3. Pointed instrument for making the holes 4. String for the indicator 5. A heavy bead for the indicator string
Last modified October 7, 1999
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