DIY History | Transcribe | Scholarship at Iowa | Eccentricity of the Sextant by Frederic Furbish, 1893 | Eccentricity of the Sextant by Frederic Furbish, 1893, Page 64

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Eccentricity of the Sextant by Frederic Furbish, 1893

Eccentricity of the Sextant by Frederic Furbish, 1893, Page 64

[page][67?][/page]
In all observations of the sun it is well to place a circular disc of stiff cardboard around the eye piece of the telescope so that the eyes may not be exposed to the dazzling glare of the sun.

[image: front and side images of a circular cardboard sun shield around telescope eyepiece]

   In observing for index error by the sun instead we proceed thus.--
   Direct the telescope to the sun, which will appear if the proper shade glasses are used as a bright well defined red disc. Bring the reflected image into the field by moving the index arm. 

[image: 3 circles vertically stacked, labeled b', a, b]

Clamp the Vernier when the two images are near and bring the upper limb of the reflected image (b) and the lower limb of the real image (a) (as seen in the field) into the position of tangency by means of a direct motion of the tangent screw.

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[page][67?][/page] In all observations of the sun it is well to place a circular disc of stiff cardboard around the eye piece of the telescope so that the eyes may not be exposed to the dazzling glare of the sun. [image: front and side images of a circular cardboard sun shield around telescope eyepiece] In observing for index error by the sun instead we proceed thus.-- Direct the telescope to the sun, which will appear if the proper shade glasses are used as a bright well defined red disc. Bring the reflected image into the field by moving the index arm. [image: 3 circles vertically stacked, labeled b', a, b] Clamp the Vernier when the two images are near and bring the upper limb of the reflected image (b) and the lower limb of the real image (a) (as seen in the field) into the position of tangency by means of a direct motion of the tangent screw.