The Antikythera Mechanism: Compound Gear-Trains for Planetary Indications

TitleThe Antikythera Mechanism: Compound Gear-Trains for Planetary Indications
Publication TypeJournal Article
Year of Publication2013
AuthorsWright, M. T.
Refereed DesignationRefereed
Journal TitleAlmagest

The decipherment of inscriptions on the Antikythera Mechanism has yielded evidence supporting a reconstruction of its front dial display in which a concentric array of pointers indicates the date and the positions of the Moon, the Sun and the five planets known in antiquity. To this is now added the reading of a parameter demonstrating that, for one planet at least, the designer knew a period-relation that describes its motion with considerable precision, and its presence in the inscription probably indicates that it was actually realized in the instrument. This could have been done only by adopting a compound train to drive the planetary mechanism. The feasibility of incorporating such compound trains for all five planets has already been demonstrated, but here we consider more fully how the Hellenistic designer might have generated tractable ratios approximating astronomical period-relations that could not be realized exactly in mechanism. The newly-discovered parameter may represent such an approximation, perhaps derived from a known Babylonian period-relation. We show that the corresponding period-relations for all five planets can be used in designing gear-trains that might easily be fitted to our existing reconstruction.

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