19th Century brass astrological volvelle. A volvelle or wheel chart is a type of slide chart. Ours is of brass construction with rotating parts. It is considered to be an early example of an analog computer. Early examples are found in the pages of astronomy books and our brass version is considered to be Indian. Abu Rayhan Biruni, circa 1000, is a Persian astronomer who made important contributions to the development of the volvelle. The plate in which the five celestial globes are mounted is engraved with a variety of astrological imagery. Both the central plate and the inner ring have small medallions with representations of the Sun, Moon and Earth. The larger outer ring has three medallions placed between each of the five celestial globes and these are engraved with figures representing some of the zodiacal signs.
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