The Quadrant

Do not confuse this with the forerunner of the sextant. It is a 90° protractor with a plumb line hanging from its vertex. Polaris is sighted along one edge and the angle where the line cuts the scale is read. As sailors were more interested in the latitude of a place rather than latitude as a number, some early quadrants replaced the degree markings with the names of ports.

The advantage of the quadrant is that you do not need to see the horizon. Most marine quadrants used a radius of 10-12 inches (30 centimetres) but the larger the quadrant the greater the spacing between degree markings and the greater its accuracy (see Figure 13.6). Tycho Brahe, the 16th century Danish astronomer, had one that filled a room.

TOP EDGE OF BOARD

FIX PLUMB LINE HERE

FIX PLUMB LINE HERE

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1. Photocopy scale, laminate and stick on piece of plywood that has at least one edge absolutely straight. This edge is the top edge of your quadrant.

2. Fix sights along top edge. These can be small nails, small brass eyes, or a narrow tube. The further apart the fore and rear sights the more accurate your sighting.

3. Attach plumb line. Use as heavy a weight as possible.

4. Some sort of handle to hold is preferable but not absolutely essential.

13.6 Quadrant

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Side pieces can sometimes make seeing the front of the cross staff difficult. Metal straps would be better if you have them.

Angled sight to make sure of sighting star with rear edge of transom

§| All joints must be ^■absolutely square, or the uouiuiciy oiwjucti vi imc transom will rock and give a false reading

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Side pieces can sometimes make seeing the front of the cross staff difficult. Metal straps would be better if you have them.

Waxing this is a real help

§| All joints must be ^■absolutely square, or the uouiuiciy oiwjucti vi imc transom will rock and give a false reading

13.7 Traditional Type Cross Staff

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