AMERICAN PENDULUM ARTIFICIAL HORIZON SEXTANT
Circa 1880
By Hall Colby. Signed on the arc plate "Hall Colby Altimiter - No. 6 Patent Applied For xxxx". A semicircular scale, divided 90-0-90 in units of 30 arc-minutes so as to indicate either altitude or zenith distance. An arc-shaped pendulum, pivoted at the center of the circle, is used to establish a horizontal line of reference. The pendulum arc carries two verniers that read to 1 arc-minute. Sights are mounted along the top of the frame. A trigger mechanism releases the pendulum to swing freely while the object is sighted and then locks the pendulum in position so that the sextant can be read.
Height 7.5". Length of tube 10".
Provenance:
West Sea Company, Old Town, San Diego, 1999.
The Kelton Collection of Marine Art & Artifacts.

Literature:
Taking to the Stars by Peter Ifland (Kreiger Publishing Co., 1988), p.108 for a discussion of this instrument.

Notes:
The only other known example of this instrument is at the Mariner's Museum in Newport News, Virginia.