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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Bedford Level experiment | 1/2 | https://en.wikipedia.org/wiki/Bedford_Level_experiment | reference | science, encyclopedia | 2026-05-05T16:17:39.125266+00:00 | kb-cron |
The Bedford Level experiment was a series of observations carried out along a 6-mile (10 km) length of the Old Bedford River on the Bedford Level of the Cambridgeshire Fens in the United Kingdom. They were performed during the 19th and early 20th centuries to deny the curvature of the Earth through measurement. 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 allow for the effects of atmospheric refraction, Alfred Russel Wallace found a curvature consistent with a spherical Earth.
== The Bedford Level == At the point chosen for all the experiments, the river is a slow-flowing drainage canal running in an uninterrupted straight line for a 6-mile (10 km) stretch to the north-east of the village of Welney. This makes it an ideal location to directly measure the curvature of the Earth, as Rowbotham wrote in Zetetic Astronomy:
If the earth is a globe, and is 25,000 English statute miles in circumference, the surface of all standing water must have a certain degree of convexity—every part must be an arc of a circle. From the summit of any such arc there will exist a curvature or declination of 8 inches in the first statute mile. In the second mile the fall will be 32 inches; in the third mile, 72 inches, or 6 feet, as shown in the following diagram:
...[A]fter the first few miles the curvature would be so great that no difficulty could exist in detecting either its actual existence or its proportion... In the county of Cambridge there is an artificial river or canal, called the "Old Bedford". It is upwards of twenty miles in length, and ... passes in a straight line through that part of the Fens called the "Bedford Level". The water is nearly stationary—often completely so, and throughout its entire length has no interruption from locks or water-gates of any kind; so that it is, in every respect, well adapted for ascertaining whether any or what amount of convexity really exists.
== Experiments ==
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 (0.9 m) above the water, row slowly away from him. He reported that the vessel remained constantly in his view for the full 6 miles (10 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 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 of the length of the canal 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, John Henry Walsh, 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 about 6 feet (1.8 m) higher than the poles at each end. This version of the experiment was taught in schools in England until photographs of the Earth from space became available, and it remains in the syllabus for the Indian Certificate of Secondary Education for 2023.