I've read Earth Not a Globe and I haven't seen anything flawed about Dr. Rowbotham's math or experiments.
Ha, read Chapter III. It says that a ball thrown upwards on a moving boat will go up, fly backwards, and land behind the boat. I'm inclined to disbelieve anyone who says something egregiously wrong like that.
Care to point out what's so flawed about looking across a body of water and measuring the amount of curvature to the earth?
Nothing at all. But, I think it is unsafe to come to the conclusion that the earth is flat from these experiments. You see, Rowbotham assumed the earth was a perfect sphere in his math. When what he saw didn't agree with this, he came to the conclusion that the entire earth was flat. There are a number of flaws. The assumption of a perfectly spherical earth is outright wrong especially on the small scale of his experiments. The oblate spheroid shape of the earth and gravitational variations due to landforms and crust irregularites cause deviations on the order of 10-100ft from a perfectly spherical water level. The result is that water can appear to have a more flat surface than would be expected. A number of studies and surveys of sea levels around the world have indeed shown this. In short, Rowbotham only showed that earth is not perfectly spherical and can appear to be locally flat at certain locations. There is no reason to conclude that the entire earth is flat from his experiments.