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The Marine Sextant, Continued
Parts and
Functions
These are the parts and functions of the marine sextant:
Part
Arc scale
Indicates the number of degrees of an angle.
Index arm
Micrometer drum
Vernier scale
Index mirror
Horizon glass
Telescope
Filters
Release levers
Description of Function
Pivots at one end to allow the attached index mirror to
reflect an object onto the horizon glass and swings
along the arc scale on the other end to indicate what
the angle measures.
Rotates to make fine adjustments when measuring
angles and indicates minutes of a degree of angle. It is
attached to the lower end of the index arm. One
complete rotation moves the index arm 1° along the arc
scale. The drum has 60 graduations, each representing
1' of arc.
Indicates tenths of a degree of angle. It is attached on
the index arm adjacent to the micrometer drum and has
10 graduations, each representing 0.1' of arc.
Reflects objects onto the horizon glass.
Allows the observer to view one object directly on one
side while observing a second object reflected next to
it. The half of the horizon glass next to the frame is
silvered to make that portion of the glass a mirror; the
other half is clear glass.
Directs the line of sight of the observer to the horizon
glass and magnifies the objects observed.
Protects the observer’s eyes when viewing the Sun.
Disengages the index arm from the arc scale to allow
the index arm to move freely.
8-25
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