The Cosmographia of Petrus Apianus was one of the most popular books on cosmography ever published. One of the reasons for the book's enormous popularity was the book's inclusion of ingenious paper devices called volvelles which enabled one to solve practical mathematical problems relating to time-telling, the calendar, and astronomy and astrology. This full-page engraving is a circular calendar consisting of an engraved disc, approximately 5 inches in diameter. At center is an allegorical representation of the sun and planets. The outer scale shows the Zodiac with each sign divided into 30 degrees. The lower left quadrant of the inner disc can be used to tell the time in unequal hours. Unequal hours, which were widely used in the 16th century, divide day and night into twelve hours each; hence they vary in length with the seasons, as do day and night. The right quadrant shows a shadow square, a proportional-measuring device often used to measure heights at a distance. A paper pointer rotates at center.

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Condition: A

Minor soil in title. Evidently an early owner replaced the original string with a paper pointer.