21.

In the instances which follow, Hipparchus, treating of these subjects, either asserts things similar to those which we have already refuted, or takes for granted matters which are not so, or draws improper sequences. For instance, from the computation [of Eratosthenes] that the distance from Babylon to Thapsacus547 is 4800 stadia, and thence northward to the mountains of Armenia548 2100 stadia more, it does not follow that, starting from the meridian of that city, the distance to the northern mountains is above 6000 stadia. Besides, Eratosthenes never says that the distance from Thapsacus to these mountains is 2100 stadia, but that a part thereof has never yet been measured; so that this argument [of Hipparchus], founded on a false hypothesis, amounts to nothing. Nor did Eratosthenes ever assert that Thapsacus lies more than 4500 stadia north of Babylon.