rmined the zenith of that place to be distant 1/50 part of the circumference of the earth from Syene, the are of the meridian between the two places being equal to 7° 12′, which was measured by the Ptolemies and found to be 500 stadia.
This gives roughly 250,000 stadia for the circumference of the earth.
The Olympic stadium was 202 3/4 yards. See odometer.
An instrument to illustrate the motions of the heavenly bodies.
It was invented by Eratosthenes about B. C. 255, and was employed till the time of Tycho Brahe, A. D. 1582.
It was ordinarily made of brass, and disposed in such a manner that the greater and lesser circles of the sphere are seen in their natural position and motion.
It was perhaps the principal agent in astronomical observations in the museum of Alexandria, which was founded by Ptolemy Soter, B. C. 298, and was plundered by Cyril A. D. 415, who probably thought the sphere was some heathenish machine for invoking the infernal gods.