This is an unusual representation of an analemma that is typically found on globes in a figure 8 pattern. Functioning like a calculator, the analemma has a movable central index arm which pivots around the center point of a 7" circle filled with lines representing time of the year and hours of the day. Aligning the index arm with degrees of latitude on the outer circle one can determine the length of the daylight for a given time of the year. This working analemma was published in the 1810 (4th edition) of the Encyclopedia Britannica.

Included with the analemma are 43 disbound pages of text and 5 additional plates on geography. Page 544 includes a detailed description on how to use the analemma.

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Condition: B

Index arm is intact and functioning well with scattered foxing. Disbound text has occasional light toning and scattered foxing.