Eratosthenes started with the premise that the earth is a sphere, and estimated the earth's circumference. He correctly assumed that the difference in the sun's daily maximum position (between locations at different latitudes) is caused by the earth's sphericity.
So Eratosthenes' calculation is definitively not a proof of the earth's sphericity, and it certainly did not convince the skeptics of his or even of much later times.
By the way, I have also made estimations not only for the number of human souls but even for
bee souls.
Why do you consider Eratosthenes' calculations which are based on the premise that the earth is a sphere, as proof of the earth's sphericity?
And why don't you consider my calculations of soul numbers, based on the premise that souls exist, as proof of the existence of souls?
By the way,
Aristarchus of Samos had already some decades before Eratosthenes made estimations of the sizes of moon and sun, and the proportion of their distances from earth. Already his poor assumption (of 87° instead of 89° 50') for the angle between sun and moon at half moon, led to the logically correct conclusion that the volume of the Sun is around 300 times greater than the earth's volume.
And the better the value assumed for the angle between sun and moon at half moon, the better the result of Aristarchus calculation, and the bigger the difference in size between sun and earth. And isn't it apriori quite implausible that the much greater surrounds the smaller?
But in the same way as Aristarchus' calculation was not considered evidence for heliocentrism for a long time, Eratosthenes' calculation had no impact on those, unable or unwilling to believe in the sphericity of the earth.
Cheers, Wolfgang
To judge from an inferior viewpoint the superior one is impossible