[Pramāṇa](https://indike.org/pramana/) › [Studies](https://indike.org/pramana/ins) › [Historical geography](https://indike.org/pramana/ins.geography) › [The Ancient Geography of India. I. The Buddhist Period, including the Campaigns of Alexander, and the Travels of Hwen-Thsang](https://indike.org/pramana/ins.geography.cunningham-1871) › c12.2 # The Ancient Geography of India. I. The Buddhist Period, including the Campaigns of Alexander, and the Travels of Hwen-Thsang c12.2 The Ancient Geography of India. I. The Buddhist Period, including the Campaigns of Alexander, and the Travels of Hwen-Thsang c12.2 - **Language:** English ### [c12.2](https://indike.org/pramana/ins.geography.cunningham-1871.c12.2) PTOLEMY'S longitudes are so manifestly in excess of the truth that various methods of rectification have been suggested by different geographers. That of M. Gossellin was to take five-sevenths of Ptolemy's measures, but his system was based upon the assumption that Ptolemy had made an erroneous estimate of the value of the degree both of the equinoctial and Rhodian diaphragms, as detailed by Eratosthenes. But for the geography of Asia, Ptolemy seems to have depended altogether upon the authority of Marinus, the Tyrian geographer, and of Titianus or Maës, a Macedonian merchant. M. Gossellin's method was probably founded upon the average of Ptolemy's errors, deduced from the longitudinal excess of many well-known places. It is in fact an empirical correction of Ptolemy's errors, of the cause of which his theory offers nothing more than a mere guess. The true sources of Ptolemy's errors of longitude have been pointed out so clearly by Sir Henry Rawlinson that I cannot do better than repeat his explanation of them.\* - [Previous: c11.32](https://indike.org/pramana/ins.geography.cunningham-1871.c11.32) - [Next: c12.3](https://indike.org/pramana/ins.geography.cunningham-1871.c12.3) - [Up: c12](https://indike.org/pramana/ins.geography.cunningham-1871.c12) --- Source: [https://indike.org/pramana/ins.geography.cunningham-1871.c12.2](https://indike.org/pramana/ins.geography.cunningham-1871.c12.2) · Pramāṇa