Note 2 — Chapter I · Exploring the Sky
Reading edition
Let C be the centre of the earth, and bCD the diameter through b. Then
BA² = Bb × BD,
where Bb = 16 feet, and BD, which is 16 feet more than the earth’s diameter = 41,900,000 feet. From this we readily calculate that BA = 25,880 feet. This calculation of course neglects the height of the hill AAʹ by comparison with the earth’s diameter.