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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Bedford Level experiment | 2/2 | https://en.wikipedia.org/wiki/Bedford_Level_experiment | reference | science, encyclopedia | 2026-05-05T09:32:01.898253+00:00 | kb-cron |
On 11 May 1904 Lady Elizabeth Anne Blount, who was later influential in the formation of the Flat Earth Society, hired a commercial photographer to use a telephoto-lens camera to take a picture from Welney of a large white sheet she had placed, the bottom edge near the surface of the river, at Rowbotham's original position 6 miles (10 km) away. The photographer, Edgar Clifton from Dallmeyer's studio, mounted his camera 2 feet (0.6 m) above the water at Welney and was surprised to be able to obtain a picture of the target, which he believed should have been invisible to him, given the low mounting point of the camera. Lady Blount published the pictures far and wide. These controversies became a regular feature in the English Mechanic magazine in 1904–05, which published Blount's photo and reported two experiments in 1905 that showed the opposite results. One of these, by Clement Stretton conducted on the Ashby Canal, mounted a theodolite on the canal bank aligned with the cabin roof of a boat. When the boat had moved one mile distant, the instrument showed a dip from the sight-line of about eight inches.
== Refraction == Atmospheric refraction can produce the results noted by Rowbotham and Blount. Because the density of air in the Earth's atmosphere decreases with height above the Earth's surface, all light rays travelling nearly horizontally bend downward, so that the line of sight is a curve. This phenomenon is routinely accounted for in levelling and celestial navigation.
If the measurement is close enough to the surface, this downward curve may match the mean curvature of the Earth's surface. In this case, the two effects of assumed curvature and refraction could cancel each other out, and the Earth will then appear flat in optical experiments. This would have been aided, on each occasion, by a temperature inversion in the atmosphere with temperature increasing with altitude above the canal, similar to the phenomenon of the superior image mirage. Temperature inversions like this are common. An increase in air temperature or lapse rate of 0.11 Celsius degrees per metre of altitude would create an illusion of a flat canal, and all optical measurements made near ground level would be consistent with a completely flat surface. If the lapse rate were higher than this (temperature increasing with height at a greater rate), all optical observations would be consistent with a concave surface, a "bowl-shaped Earth". Under average conditions, optical measurements are consistent with a spherical Earth approximately 15% less curved than in reality. Repetition of the atmospheric conditions required for each of the many observations is not unlikely, and warm days over still water can produce favourable conditions.
== Similar experiments conducted elsewhere == On 25 July 1896, Ulysses Grant Morrow, a newspaper editor, conducted a similar experiment on the Old Illinois Drainage Canal, Summit, Illinois. Unlike Rowbotham, he was seeking to demonstrate that the surface of the Earth was curved: when he too found that his target marker, 18 inches (46 cm) above water level and 5 miles (8 km) distant, was clearly visible, he concluded that the Earth's surface was concavely curved, in line with the expectations of his sponsors, the Koreshan Unity society. The findings were dismissed by critics as the result of atmospheric refraction.
== See also == History of geodesy The Final Experiment (expedition)
== Notes ==
== References == Michell, John (1984). Eccentric Lives and Peculiar Notions. London: Thames and Hudson. ISBN 0-500-01331-4.