https://en.wikipedia.org/wiki/Bedford_Level_Experiment
(unsubstantiated, but hilarious): “If the measurement is close enough to the surface, light rays can curve downward at a rate equal to the mean curvature of the Earth’s surface. In this case, the two effects of curvature and refraction cancel each other out and the Earth will appear flat in optical experiments.”
…”an increase in air temperature … of 0.11 degrees Celsius per metre of altitude would create an illusion of a flat canal, … [or if] higher than this … all optical observations would be consistent with a concave surface, a “bowl-shaped earth””
…”Ulysses Grant Morrow, … found that his target marker, eighteen inches above water level and five miles distant, was clearly visible he concluded that the Earth’s surface was concavely curved”
(the history of maps and globe representations of the Earth is full of wonderful things like this)