You know, then, that you might be in a place where one of those two
bright stars would be overhead, and you might journey on to another
place further south, where the other one would be at the zenith or
overhead.
This is all clear to me.
Then if you measured the ground you had gone over, it would be equal to
one-ninetieth part of the space between the pole and the equator, or
about seventy miles. Can you tell how many miles it would be from the
pole to the equator?
That would be seventy times ninety--which is 6300.
But that is only one-quarter of the way round--is it not?
Yes; the whole distance round would be four times 6300, or about 25,000
miles.
Well done--we have measured the circumference of the world.”