m of Thales' sphere, and for pinpointing its creation at a specific point in time. However, it is clearly a simplification of events that occurred several hundred years before Cicero's lifetime. Why would Thales' create a spherical representation of the heavens and neglect to indicate the stars? Of what use is a bowling ball for locating celestial bodies? Considering Eudoxus' preoccupation with systems of concentric spheres, a more logical explanation is that Thales marked his sphere with stars, and Eudoxus later traced the ecliptic and the paths of the planets on the exterior. The celestial sphere in question probably resembled this early Persian example. Perhaps the most famous celestial sphere is the mechanized globe attributed to Archimedes. Cicero was especially impressed by this invention because of its ability to imitate "the motions of the sun and moon and of those five stars which are called wanderers" with a single rotational focus (Price 56). By turning a crank, one could observe the "natural" course of the sun, moon and planets around the earth. The sphere was also remarkable for a second reason. Unlike a stationary globe, like that of Thales' and Eudoxus, a mechanized sphere requires gears to accurately represent the motion of the heavens. According to Prof. Derek Price, the mean period of Saturn can be mechanically represented by a gear ratio of 30 to 1. In other words, for every revolution of the sun around the earth, Saturn will only accomplish 1/30th of its revolution around the earth. The mean period of Jupiter can be represented by a gear ratio of 12 to 1, and Mars can be represented by a gear ratio of 2.5 to 1. An interesting problem arises when one attempts to mechanically represent the synodic month. A gear ratio of 235 to 19 is required for an accurate representation. However, this is impossible to achieve directly, presenting a serious challenge to Archimedes and other Greek scientists. Prof. Price claims that tw...
