Yazeed asked:

Who discovered that the world is round? When and how did it happen?

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I looked up the answer to your question in the Grolier 97 Multimedia Encyclopaedia.Here's an extract
from the article, Earth, size and shape of:

The shape of the Earth was considered to be a sphere by ancient Greeks such as Pythagoras and
Aristotle. The first accurate measurement of the Earth's size was made in the 3rd century BC by
Eratosthenes of Cyrene. He knew that at the summer solstice, the first day of summer, the noon Sun
was reflected in a well dug at Syene (modern Aswan). This fact indicated that Syene was
approximately on a direct line between the Sun and the Earth's center. Simultaneously, Eratosthenes
determined that the Sun as observed at Alexandria (which he assumed to be on the same meridian
as Syene) was south of the vertical by about 1/50 of a full circle. Because the rays of the distant Sun
striking Syene and Alexandria can be assumed parallel, the angle of shadow at Alexandria is equal to
the angle between there and Syene, as measured from the center of the Earth. The Earth's
circumference would thus be 50 times the north-south distance between the sites. No way existed
then to determine this distance accurately, but Eratosthenes' value was correct probably to within 15
percent.

That's the historical facts sorted out. I'm still puzzled by how Pythagoras or Aristotle could have
accepted that the earth was spherical, in the absence of a theory that accounted for the observation
that 'Things generally fall down' in terms of a notion of gravitational attraction.

Children are taught in school that the earth is round, and most accept this, in the face of apparently
conclusive evidence to the contrary. If the earth was round, then surely the people in Australia would
fall off? Or, if some kind of glue is holding them on, why doesn't it feelto them as if they're hanging
upside down?

Or suppose the teacher is sufficiently smart to discuss the round earth theory along with Newton's
theory of gravitation, and how Newtonian mechanics accounts for the orbits of the planets in the solar
system. Aren't they worried about how physical action can occur at a distance?

Then, of course, there are those - like a student I once taught - who have never 'learned' this lesson,
who believe that the round earth theory is a gigantic conspiracy perpetrated by the scientific
community.

In the name of free speech and democracy, isn't it time we insisted that children are given lessons in
both the flat earth and round earth theories, so that they can decide for themselves which theory to
believe?!

Geoffrey Klempner