– Lack of visible or measurable curvature: The horizon looks flat to the eye. Researchers have claimed that the skyline of cities such as New York City and Philadelphia are visible 40-60 miles away from the ground, when the alleged curvature of the Earth should not permit them to be seen. The famous Bedford Canal experiment performed in 1838 by Samuel Rowbotham showed that a canoe or small boat was visible from 6 miles away along a river (when the curvature of the earth should have rendered it invisible below the horizon or line of sight).