We will now return at once to Hipparchus, and see
what comes next. Continuing to palm assumptions of his own
[upon Eratosthenes], he goes on to refute, with geometrical
accuracy, statements which that author had made in a mere
general way. Eratosthenes,

he says, estimates that there
are 6700 stadia between Babylon and the Caspian Gates,
and from Babylon to the frontiers of Carmania and Persia
above 9000 stadia; this he supposes to lie in a direct line
towards the equinoctial rising,

The
hypotenuse of the supposed triangle, or the line drawn from Babylon to
the Caspian Gates being only 6700 stadia, would be necessarily shorter
than either of the other sides, since the line from Babylon to the frontiers of Carmania is estimated by Eratosthenes at 9170, and that from
the frontiers of Carmania to the Caspian Gates above 9000 stadia.
The frontiers of Carmania would thus be east of the Caspian Gates,
and Persia would consequently be comprised, not in the third, but in the
second section of Eratosthenes, being east of the meridian of the Caspian
Gates, which was the boundary of the two sections.

Strabo, in the text,
points out the falsity of this argument.

To this we reply, that the line drawn from Babylon to Carmania was never intended as a parallel, nor yet that which
divides the two sections as a meridian, and that therefore nothing has been laid to his charge, at all events with any just
foundation. In fact, Eratosthenes having stated the number
of stadia from the Caspian Gates to Babylon as above
given,according to these premises, the meridian drawn from the Gates of
the Caspian will intersect the parallel of Babylon and Susa
4400 stadia more to the west, than would a straight line
drawn from the Caspian to the confines of Carmania and
Persia; and that this last line, forming with the meridian of
the Caspian Gates half a right angle, would lie exactly
in a direction midway between the south and the equinoctial
rising. Now as the course of the Indus is parallel to this
line, it cannot flow south on its descent from the mountains, as
Eratosthenes asserts, but in a direction lying between the
south and the equinoctial rising, as laid down in the ancient
charts.

But who is there who will admit this to be an obtuse-angled triangle, without also admitting that it contains a
right angle? Who will agree that the line from Babylon to
Susa, which forms one side of this obtuse-angled triangle, lies
parallel, without admitting the same of the whole line as far
as Carmania? or that the line drawn from the Caspian Gates
to the frontiers of Carmania is parallel to the Indus? Nevertheless, without this the reasoning [of Hipparchus] is worth
nothing

Eratosthenes himself also states,

[continues Hipparchus,that the form of India is rhomboidal; and since the whole
eastern border of that country has a decided tendency towards the east, but more particularly the extremest cape,