Bedford Level experiment
Encyclopedia
The Bedford Level Experiment is a series of observations carried out along a six-mile length of the Old Bedford River
on the Bedford Level, Norfolk
, England, during the nineteenth and early twentieth centuries. It was an attempt to determine the shape of the Earth
. Early results seemed to prove the Earth to be flat, but most later attempts to reproduce the observations firmly supported the established view that the earth is a sphere.
. The most famous of the observations, and the one that was taught in schools until photographs of the Earth from space became available, involved a set of three poles fixed at equal height above water level along this length. As the surface of the water was assumed to be level, the discovery that the middle pole, when viewed carefully through a theodolite
, was almost three feet higher than the poles at each end was finally accepted as a new proof that the surface of the earth was indeed curved.
(1816–1884), in the summer of 1838. He waded into the river and used a telescope held eight inches above the water to watch a boat with a five-foot mast row slowly away from him. He reported that the vessel remained constantly in his view for the full six miles 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 some eleven feet below his line of sight. He published this discovery under the title Zetetic Astronomy using the pseudonym Parallax in 1849 and subsequently expanded it into a book 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 step was to set a sight line 4 metres (13.1 ft) above the water.
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 libel and threatening to kill Wallace.
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 geography reader
at King's College, Cambridge
, conducted the definitive experiment described in "Method", above.
The planists
, however, were not yet defeated: On 11 May 1904 Lady Elizabeth Anne Blount hired a commercial photographer to use a telephoto lens camera to take a picture from Welney of a large white sheet she had placed, touching the surface of the river, at Rowbotham's original position six miles away. The photographer, Edgar Clifton from Dallmeyer's studio
, mounted his camera two feet above the water at Welney and was surprised to be able to obtain a picture of the target, which should have been invisible to him given the low mounting point of the camera. Lady Blount published the pictures far and wide and for those who do not accept the explanation of Superior Mirage due to refraction
, these have not been explained.
These controversies became a regular feature in the English Mechanic magazine in 1904–5, 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 4 in 9 in (1.45 m) above the surface.
.
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.
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 degrees Celsius
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 its true diameter. 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.
. Unlike Rowbotham, he was seeking to demonstrate that the surface of the earth was curved: when he too 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, in line with the expectations of his sponsors, the Koreshan Unity
society. The findings were dismissed by critics as the result of atmospheric refraction.
Old Bedford River
The Old Bedford River is an artificial, partial diversion of the waters of the River Great Ouse in the Fens of Cambridgeshire, England. It was named after the fourth Earl of Bedford who contracted with the local Commission of Sewers to drain the Great Level of the Fens beginning in 1630.The idea of...
on the Bedford Level, Norfolk
Norfolk
Norfolk is a low-lying county in the East of England. It has borders with Lincolnshire to the west, Cambridgeshire to the west and southwest and Suffolk to the south. Its northern and eastern boundaries are the North Sea coast and to the north-west the county is bordered by The Wash. The county...
, England, during the nineteenth and early twentieth centuries. It was an attempt to determine the shape of the Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
. Early results seemed to prove the Earth to be flat, but most later attempts to reproduce the observations firmly supported the established view that the earth is a sphere.
Method
At the point chosen for all the experiments the river is a slow-flowing drainage canal running in an uninterrupted straight line for a six-mile stretch to the north-east of the village of WelneyWelney
Welney is a village and civil parish in the Fens of England, and the county of Norfolk. The village is situated immediately to the west of parallel Old Bedford River, River Delph and New Bedford River, which are here crossed by the A1101 road. The village is some south-west of the town of Downham...
. The most famous of the observations, and the one that was taught in schools until photographs of the Earth from space became available, involved a set of three poles fixed at equal height above water level along this length. As the surface of the water was assumed to be level, the discovery that the middle pole, when viewed carefully through a theodolite
Theodolite
A theodolite is a precision instrument for measuring angles in the horizontal and vertical planes. Theodolites are mainly used for surveying applications, and have been adapted for specialized purposes in fields like metrology and rocket launch technology...
, was almost three feet higher than the poles at each end was finally accepted as a new proof that the surface of the earth was indeed curved.
History
The first investigation was carried out by Samuel Birley RowbothamSamuel Rowbotham
Samuel Birley Rowbotham was an English inventor and writer who wrote Zetetic Astronomy: Earth Not a Globe under the pseudonym "Parallax". His work was based on his decade-long studies of the earth and was originally published as a 16-page pamphlet , which he later expanded into a 430 page book...
(1816–1884), in the summer of 1838. He waded into the river and used a telescope held eight inches above the water to watch a boat with a five-foot mast row slowly away from him. He reported that the vessel remained constantly in his view for the full six miles 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 some eleven feet below his line of sight. He published this discovery under the title Zetetic Astronomy using the pseudonym Parallax in 1849 and subsequently expanded it into a book 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
Alfred Russel Wallace
Alfred Russel Wallace, OM, FRS was a British naturalist, explorer, geographer, anthropologist and biologist...
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 step was to set a sight line 4 metres (13.1 ft) above the water.
Despite Hampden initially refusing to accept the demonstration, Wallace was awarded the bet by the referee, editor of The Field
The Field (magazine)
The Field is the world's oldest country and field sports magazine, having been published continuously since 1853.The famous sportsman Robert Smith Surtees, the creator of Jorrocks, was the driving force behind the initial publication...
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 libel and threatening to kill Wallace.
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
Henry Yule Oldham
Henry Yule Oldham, was a teacher and geographer who, in 1901, conducted the definitive version of the Bedford Level experiment, a proof that the Earth is a sphere.-Early life:...
, a geography reader
Reader (academic rank)
The title of Reader in the United Kingdom and some universities in the Commonwealth nations like Australia and New Zealand denotes an appointment for a senior academic with a distinguished international reputation in research or scholarship...
at King's College, Cambridge
King's College, Cambridge
King's College is a constituent college of the University of Cambridge, England. The college's full name is "The King's College of our Lady and Saint Nicholas in Cambridge", but it is usually referred to simply as "King's" within the University....
, conducted the definitive experiment described in "Method", above.
The planists
Flat Earth Society
The Flat Earth Society is an organization that seeks to further the belief that the Earth is flat instead of an oblate spheroid. The modern organization was founded by Englishman Samuel Shenton in 1956 and was later led by Charles K...
, however, were not yet defeated: On 11 May 1904 Lady Elizabeth Anne Blount hired a commercial photographer to use a telephoto lens camera to take a picture from Welney of a large white sheet she had placed, touching the surface of the river, at Rowbotham's original position six miles away. The photographer, Edgar Clifton from Dallmeyer's studio
Thomas Rudolphus Dallmeyer
Thomas Rudolphus Dallmeyer , English optician, was the son of John Henry Dallmeyer who ran an optics business.He assumed control of the business on the failure of his father's health, was principally known as the first to introduce the telephoto lens into ordinary practice , and he was the author...
, mounted his camera two feet above the water at Welney and was surprised to be able to obtain a picture of the target, which should have been invisible to him given the low mounting point of the camera. Lady Blount published the pictures far and wide and for those who do not accept the explanation of Superior Mirage due to refraction
Atmospheric refraction
Atmospheric refraction is the deviation of light or other things like humanelectromagnetic wave from a straight line as it passes through the atmosphere due to the variation in air density as a function of altitude...
, these have not been explained.
These controversies became a regular feature in the English Mechanic magazine in 1904–5, 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 4 in 9 in (1.45 m) above the surface.
Refraction
Refraction of light 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. This phenomenon is routinely allowed for in levelling and celestial navigationCelestial navigation
Celestial navigation, also known as astronavigation, is a position fixing technique that has evolved over several thousand years to help sailors cross oceans without having to rely on estimated calculations, or dead reckoning, to know their position...
.
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.
This would have been aided, on each occasion, by a temperature inversion
Inversion (meteorology)
In meteorology, an inversion is a deviation from the normal change of an atmospheric property with altitude. It almost always refers to a temperature inversion, i.e...
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
Lapse rate
The lapse rate is defined as the rate of decrease with height for an atmospheric variable. The variable involved is temperature unless specified otherwise. The terminology arises from the word lapse in the sense of a decrease or decline; thus, the lapse rate is the rate of decrease with height and...
of 0.11 degrees Celsius
Celsius
Celsius is a scale and unit of measurement for temperature. It is named after the Swedish astronomer Anders Celsius , who developed a similar temperature scale two years before his death...
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 its true diameter. 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.
Other experiments
On July 25, 1896, Ulysses Grant Morrow, a newspaper editor, conducted a similar experiment on the Old Illinois Drainage Canal, Summit, IllinoisSummit, Illinois
Summit is a village in Cook County, Illinois, United States. The population was 10,637 at the 2000 census. The village is best known as the setting to Ernest Hemingway's 1927 short story "The Killers".-Geography:...
. Unlike Rowbotham, he was seeking to demonstrate that the surface of the earth was curved: when he too 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, in line with the expectations of his sponsors, the Koreshan Unity
Koreshanity
Not to be confused with the teachings of David KoreshKoreshanity is the set of religious/scientific beliefs put forth by Cyrus Teed...
society. The findings were dismissed by critics as the result of atmospheric refraction.