E·ra·tos·the·nes 
(ĕr′ə-tŏsthə-nēz′) Third century BC.
(ĕr′ə-tŏsthə-nēz′) Third century BC. Greek mathematician, astronomer, and geographer who devised a map of the world, estimated the circumference of the earth and the distance to the moon and the sun, and constructed a method for finding prime numbers.