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eastern meridian was that which passed through the Metropolis of the Sinai, which he calls Sinai or Thinai, and places in 180° 40′ E. Long. and 3° S. Lat. The distance of this meridian from that of Alexandria he estimated at 119½ degrees, and the distance of the first meridian from the same at 60½ degrees, making together 180 degrees, or exactly one-half of the circumference of the earth. His estimate of the breadth he obtained by fixing the southern limit of the inhabited parts in the parallel of 16¼ degrees of South Latitude, which passes through a point as far south of the Equator as Meroë is north of it. And by fixing the northern limit in the parallel of 63 degrees North Latitude, which passes through Thoulê (probably the Shetland Islands), a space of nearly 80 degrees was thus included between the two parallels, and this was equivalent in Ptolemy’s mode of reckoning to 40,000 stadia.
Having made these determinations he had next to consider in what mode the surface of the earth with its meridians of longitude and parallels of latitude should be represented on a sphere and on a plane surface—of the two modes of delineation that on the sphere is the much easier to make, as it involves no method of projection, but a map drawn on a plane is far more convenient for use, as it presents simultaneously to the eye a far greater extent of surface. Marinos had drawn his map of the world on a plane, but his method
of a degree along the Equator, and 6° 50′ must be added bocause Ferro was so much further west than ho supposed. Subject to those corrections his longitudes would be fairly accurate, provided his calculations of distances were otherwise free from error.
