About the same time Crates of Mallus (d. 145 B.C.) embodied the views of the Stoic school of philosophy in a globe which has become typical as one of the insignia of royalty. On this globe an equatorial and a meridional ocean divide our earth into four quarters, each inhabited, thus anticipating the discovery of North and South America and Australia.
The period between Eratosthenes and Marinus of Tyre was one of great political importance. Military operations added to our knowledge of the world but scientific cartogrlphy was utterly neglected.
Among Greek works written during this period there are sev eral which either give us an idea of the maps available at that time, or furnish information of direct service to the compiler of a map. Among the latter a Periplus or coastal guide of the Ery threan sea, which clearly reveals the peninsular shape of India (A.D. 90) and Arrian's Periplus Ponti Euxeni (A.D. 131) which Festus Avienus translated into Latin. Among geographers should be mentioned Posidonius (13o-5o B.c.), the head of the Stoic school of Rhodes, who is stated to be responsible for having re duced the length of a degree to 500 stadia; Artemidorus of Eph esus, whose "Geographumena" (c. ioo B.c.) are based upon his own travels and a study of itineraries, and above all, Strabo, who adhered to the scientific theories of Eratosthenes.
The credit of having returned to the scientific principles intro duced by Eratosthenes and Hipparchus is due to Marinus of Tyre (c. A.D. 120). His map and the descriptive accounts which accom panied it have perished, but we learn sufficient concerning them from Ptolemy to be able to appreciate their merits and demerits. Marinus was the first who laid down the position of places on a projection according to their latitude and longitude, but the pro jection used by him was of the rudest. Parallels and meridians were represented by straight lines intersecting each other at right angles, the relative proportions between degrees of longitude and latitude being retained only along the parallel of Rhodes. The distortion of the countries represented would thus increase with the distance, north and south, from this central parallel. The number of places whose position had been determined by as tronomical observation was as yet very small, and the map had thus to be compiled mainly from itineraries furnished by travellers or the dead reckoning of seamen. The errors of distance were still further increased by his assuming a degree to be equal to soo stadia. There was a list of places arranged according to latitude
and longitude. It must have been much in demand, for three edi tions of it were prepared. Masudi (loth century) saw a copy of it and declared it to be superior to Ptolemy's map.
Ptolemy (q.v.) was the author of a Geography (c. A.D. 15o) in eight books. "Geography," in the sense in which he uses the term, signifies the delineation of the known world, in the shape of a map, while chorography carries out the same object in fuller detail, with regard to a particular country. In Book I. he deals with the principles of mathematical geography, map pro jections and sources of information. Books II. to VII. index the longitudes, and thus it is possible to reconstruct the maps.
Ptolemy's great merit consists in having accepted the views of Hipparchus with respect to a projection suited for a map of the world. Of the two projections proposed by him one is a modified conical projection with curved parallels and straight meridians; in the second projection (see fig. 2) both parallels and meridians are curved. The correct relations in the length of degrees of latitude and longitude are maintained in the first case along the latitude of Thule and the equator, in the second along the parallel of Agisymba, the equator and the parallels of Meroe, Syene and Thule. Following Hipparchus he divided the equator into 36o° drawing his prime meridian through the Fortunate islands.
As a map compiler Ptolemy does not take a high rank. In the main he copied Marinus whose work he revised and supple mented in some points, but he failed to realize the peninsular shape of India, erroneously exaggerated the size of Taprobane (Ceylon), and suggested that the Indian ocean had no connection with the western ocean, but formed Mare Clausum. Ptolemy knew but of a few latitudes which had been determined by actual observation, while of three longitudes resulting from simultaneous observation of eclipses he unfortunately accepted the least satis factory, namely, that which placed Arbela to the east of Carthage, while the actual meridian distance only amounts to An even graver source of error was Ptolemy's acceptance of a degree of Soo stadia (fig. 2). But in spite of his errors the scientific method pursued by Ptolemy was correct, and though he was neglected by the Romans and during the middle ages, once he had become known, in the 15th century, he became the teacher of the modern world.