Of course, a lot of people do believe in a(n approximately) spherical earth for poor reasons. My father used to cite the fact that ships disappear over the horizon a little bit at a time - which indicates curvature but not necesarily a complete sphere.
There is no magic bullet that definitively proves a spherical earth; it's an accumulation of little bits of evidence. Like evolution, it's easy to argue against individual points but it's unreasonable to disregard the whole weight of evidence at once.
It's often been noted by the society that round earthers will suggest what they think would be experiments which would falsify a flat earth, but that they seem to lack the confidence to actually go out and do them.
I remember reading about an experiment that was done a hundred years or so ago in England:
There was a stretch of canal that was perfectly straight for six miles or so. They set up markers at a fixed height above the water at each end and in the middle. Sighting along the markers, it was observed that they fell in a straight line, indicating that the surface of the water was perfectly flat.
Unfortunately, the actual data has been lost and the canal no longer exists.
Do the physics and you will find this is only true on a flat Earth. In fact, we Round Earthers believe that if a bullet is fired level fast enough (>11.2 km/s) it will never hit the ground!
As long as gravity is orthogonal to the surface, I don't think it makes any difference whether the surface is flat or convex - gravity will pull the bullet toward the surface. To fit the physics, a flat earth would need "lines of gravity" that were parallel instead of convergent at the center of mass. The theory would be different but the observations would be the same.
As for escape velocity, the question is: What happens to gravity when you're beyond the edge of the flat earth? That would depend on the alternate theory of how gravity works.
I must admit I was surprised myself at the difference the Earth's curvature could make over a few kilometers. I wonder where we could find a flat (i.e. spherical) plain of sufficient extent to confirm this experimentally?
No, we think it's 149.6 million km. I asked you what they think.
In Message 62 you said, "They claim these rays ought to be vertical and parallel (as I also envisage) but that their angled rays show that the sun is not far from us." So how far from us do "they" think the sun is?
The point being that we have other ways of measuring the distance to the sun. Even if the crepuscular thingy was a valid, it wouldn't negate everything else we know. There is no silver bullet.
A silver bullet is a magic weapon - one shot and you win. My point was that you can't have one magic argument against a flat earth or against evolution or against anything else. One point against it doesn't defeat it.
You don't have to take that as a personal insult.
So far no one has helped me understand anything apart from this stupid war.