One argument that was used to persuade Bullinger to accept flat earth theory was this one :
"On May 11, 1904 Lady Anne Blount hired a commercial photographer to use a telephoto lens camera to take a picture from Welney of a large white sheet she had placed, touching the surface of the river, at
Rowbotham's original position six miles away. The photographer, Edgar Clifton from Dallmeyer'sstudio, mounted his camera two feet above the water at Welney and was surprised to be able to obtain a
picture of the target, which should have been invisible to him if Earth where spherical."
This argument is untrue. Was dis-proven since then many times. The distance needed is greater "than six miles away"
and was never accomplished in any way that showed the earth is flat.
The curvature of the earth is so flat as greater distances, because the earth is so huge, the object is still visible at over six miles on a global earth.