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European, circa 1800.


Unsigned. Inscribed on the inner most dial "Instrumentum Lunare." Constructed of rigid laminated card. The main disk set with three graduated volvelles of heavy card, all turning on a common center. The disks turn within a pierced and decorated suspension strap of brass, the time indicator is against a rotating brass alidade. The faces of disk and volvelles are precisely divided with the scales drawn in ink, and annontated in Latin. There is additional hand coloring to accentuate the scale divisions and the rendering of the Zodiac figures.

The outermost scale starts with the annotation "27d 7h 43m 4s" representing the exact time it takes for one lunar circuit of the earth, back to the same ecliptic longitude. This scale runs from 0 to 31 days, each day subdivided to hours. Thirty years, from 1800 to 1830, are indicated on this scale. The next ring is a calendar volvelle with days, Zodiac positions, and annual lunar waning and waxing. The next volvelle has a spiral scale of days, and years from 1800 to 1932 (sic). Finally the central volvelle is replete with six sophisticated scales including the horizontal parallax of the moon, its apparent diameter, the earth-moon distance, etc. It is complete even with the little silk "handles" for rotation and is fully functional.
Diameter 18.5".
Condition: Excellent, The computer is in very fine condition, noting slight fading and soiling.

  • Provenance:
    Tesseract, Hastings on Hudson, NY, 2013
    The Kelton Collection of Marine Art & Artifacts.

    There is a long tradition of manuscript (paper) instruments, ranging from astrolabes to globes, from sundials and quadrants to portulans and astrologic diagrams. This example, precisly constructed circa 1800, with calculations carried forward for 132 years.

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