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Eccentricity of the Sextant by Frederic Furbish, 1893

Eccentricity of the Sextant by Frederic Furbish, 1893, Page 39

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32 The arc is about 120° in extent and the graduations are marked on a silver strip about 1/4'' in width inlaid in the brass of the arc. The 0 of the arc is very near it's right extremity. To the right of 0 the graduations run to 345° or 15° in extent and on the left to 135°; here there is a -eak, the graduations continue but the 10° numbers are not marked (see photograph) until 180° is reached. From that point the graduations extend to the left to 250°. The reason for this -eak of about 40° is that the rays of light are cut off from the index glass by the prism and telescope when the angle reaches about 140°. Angles of this magnitude are measured by reversing the sextant, that is, instead of holding the instrument
 
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