If light bends upwards, the sinking effect occurs.
Rowbotham seems to disagree. He invokes "The Laws of Perspective" in ENAG Chapt. XIV:
"From the several cases now advanced, which are selected from a great number of instances involving the same law, the third proposition (on page 203) that "any distinctive part of a body will become invisible before the whole or any larger part of the same body," is sufficiently demonstrated. It will therefore be readily seen that the hull of a receding ship obeying the same law must disappear on a plane surface, before the mast head. If it is put in the form of a syllogism the conclusion is inevitable:--
Any distinctive part of a receding object becomes invisible before the whole or any larger part of the same object."
After Rowbotham's publications some scientists paid attention to their research.
There were undoubtedly many scientists of all kinds who could have pointed out that Rowbotham's results were comfortably explained by the refraction of light near a hot surface, the basis of many desert mirages. However, no one seemed interested until the experienced Alfred Russel Wallace, conceived a rather more elaborate experiment. In part, this was because one John Hampden of Swindon had subscribed to a £ 1,000 bet stating that a new experiment would establish the flatness of the earth for all time
On March 5, 1870, the knights John Hampden, Alfred Wallace, William Carpenter (witness on behalf of Hampden), MWB Coulcher (witness on behalf of Wallace) and JH Walsh, editor of the newspaper "The Field" met on the Old Bedford River. "and referee agreed to the challenge.
The iron parapet of the Welney Bridge was 4.04 m. above the canal water. The old Bedford Bridge, about 9.6 km away, was brick and a little higher. On this bridge, a large sheet of white calico, of 1.80 m, was fixed. long and 0.90 m. wide, with a wide black band along the center; the lower edge of which was at the same height from the water as the parapet of the Welney bridge; so that the center of it would be as high as the line of sight of the large six-inch telescope that Wallace brought. At the central point, about three miles from each bridge, a long pole with two red discs was fixed on it, the upper one, which had the same height above the water at its center as the center of the black band on the calico and of the telescope, while the second disk was 1.22 m. below. It is clear that if the surface of the water is a perfectly straight line for 9.6 km, the three objects: the telescope, the upper disk, and the black band would be perfectly aligned at the same height above the water, the disk would have to be seen in the telescope projected on the band of black color; while, if the surface of the water is convexly curved, then the upper disc would have to be higher than the black colored band, such difference in height, due to the known size of the earth, should be 1.57 meters , what amount will be reduced a little by refraction to perhaps 1,50 m.
https://4.bp.blogspot.com/-SmE5an_x8wU/WPwUAvtvuNI/AAAAAAAAAG4/7ikWA48jhRoFcQOn4J3g6lM93_PBuLZEgCLcB/s1600/1905_Wallace_A237.2_fig399.jpghttps://1.bp.blogspot.com/-tFoXowO8bEk/WPwSNrHKc6I/AAAAAAAAAGk/Ra4D2--yqgQc4Sc-0L8bnpOvCYrStXB1ACLcB/s1600/1905_Wallace_A237.2_fig400.jpgThe experiment, in practice, is not as easy as in theory. To avoid susceptibilities, you have to be extremely careful in measuring the heights and positions of the targets and the telescope. You have to be lucky with visibility conditions, and take into account things such as the refraction of light caused by the atmosphere, which is noticeable at a distance of six miles, and varies according to the time of day and atmospheric conditions.
The result of the experiment was the predictable: The central target appeared elevated on the telescope-bridge visual line about five and a half feet (1.68 m), giving the reason to Wallace. A calculation made by taking a land radius of 6371 km. and a distance between each mark of 4,828 km. yields the result that the center mark should have appeared at 1.83m. on the visual line. Given the circumstances, it seems a pretty good result.
Walsh determined that the Earth's curvature was proven, and handed the money to Wallace, the winner.
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