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The Sailor's Word-Book

A name formerly given to a peculiar sea-quadrant, because the back of the observer was turned towards the sun at the time of observing its zenith distance. The inventor was Captain Davis, the Welsh navigator, about 1590. It consists of a graduated arc of 30° united to a centre by two radii, with a second arc of smaller radius, but measuring 6° on the side of it. To the first arc a vane is attached for sight, to the second one for shade, and at the vertex the horizontal vane has a slit in it.

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