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Eccentricity of the Sextant by Frederic Furbish, 1893

Eccentricity of the Sextant by Frederic Furbish, 1893, Page 27

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20 D and E are the sights which, when directed to a heavenly body, indicate it's altitude by means of the plumb-line. EF hanging in front of the quadrant arc. Up to 1729 all instruments depended on the plumb-line or required the observer to kook in two directions. In that year Pierre Bouger pointed out these defects and suggested this form. The sun's rays pass through A and illuminate the peg B. By altering the position of the sight vane C while keeping the sun's rays on the peg the rays from the horizon are are made to pass the peg and through the sight vane to the eye. The position of C on the arc
 
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