page_title: Bedford Level experiment
section_title: Experiments
hierarchical_section_title: Bedford Level experiment / Experiments
caption_attribution_description: English: Illustration to Chapter 2, "Experiments", of Earth not a globe by Samuel Birley Rowbotham, published by Shirley, Marshall and Co, London, in 1881, oclc 29711500.
context_page_description: The Bedford Level experiment is a series of observations carried out along a 6-mile length of the Old Bedford River on the Bedford Level of the Cambridgeshire Fens in the United Kingdom, during the 19th and early 20th centuries, to measure the curvature of the Earth. Samuel Birley Rowbotham, who conducted the first observations starting in 1838, claimed that he had proven the Earth to be flat. However, in 1870, after adjusting Rowbotham's method to avoid the effects of atmospheric refraction, Alfred Russel Wallace found a curvature consistent with a spherical Earth.
context_section_description: The first experiment at this site was conducted by Rowbotham in the summer of 1838.  He waded into the river and used a telescope held 8 inches (20 cm) above the water to watch a boat, with a flag on its mast 3 feet (0.91 m) above the water, row slowly away from him. He reported that the vessel remained constantly in his view for the full 6 miles (9.7 km) to Welney bridge, whereas, had the water surface been curved with the accepted circumference of a spherical Earth, the top of the mast should have been about 11 feet (3.4 m) below his line of sight. He published this observation using the pseudonym Parallax in 1849 and subsequently expanded it into a book Earth Not a Globe published in 1865.
  Rowbotham repeated his experiments several times over the years, but his claims received little attention until, in 1870, a supporter by the name of John Hampden offered a wager that he could show, by repeating Rowbotham's experiment, that the Earth was flat. The noted naturalist and qualified surveyor Alfred Russel Wallace accepted the wager. Wallace, by virtue of his surveyor's training and knowledge of physics, avoided the errors of the preceding experiments and won the bet.
  The crucial steps were:
  To set a sight line 13 feet (4.0 m) above the water, and thereby reduce the effects of atmospheric refraction.
  To add a pole in the middle that could be used to see the "bump" caused by the curvature of the Earth between the two end points.
  Despite Hampden initially refusing to accept the demonstration, Wallace was awarded the bet by the referee, editor of The Field sports magazine.
  Hampden subsequently published a pamphlet alleging that Wallace had cheated and sued for his money. Several protracted court cases ensued, with the result that Hampden was imprisoned for threatening to kill Wallace and for libel.
  The same court ruled that the wager had been invalid because Hampden retracted the bet and required that Wallace return the money to Hampden.
  Wallace, who had been unaware of Rowbotham's earlier experiments, was criticized by his peers for "his 'injudicious' involvement in a bet to 'decide' the most fundamental and established of scientific facts".
  In 1901, Henry Yule Oldham, a reader in geography at King's College, Cambridge, reproduced Wallace's results using three poles fixed at equal height above water level.  When viewed through a theodolite, the middle pole was found to be almost 3 feet (0.91 m) higher than the poles at each end.  This version of the experiment was taught in schools until photographs of the Earth from space became available.
  Advocates of a flat Earth, however, were not deterred: on 11 May 1904 Lady Elizabeth Anne Blount, who would go on to be 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 (9.7 km) away. The photographer, Edgar Clifton from Dallmeyer's studio, mounted his camera 2 feet (0.61 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 Stratton on the Ashby Canal, showed a dip on a sight-line only above the surface.
caption: Diagram of Rowbotham's experiment on the Bedford Level, taken from his book "Earth not a globe"
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