The Bedford Level experiment

In 1838, an eccentric British inventor named Samuel Birley Rowbotham attempted to demonstrate that the Earth is flat, using a long stretch of water known as the Bedford Level. Rowbotham’s views were based on the Hebrew cosmology of the Old Testament, which depicts a three-tiered cosmos with the heavens above, the earth in the middle, and the underworld below.

In support of his Flat Earth model, Rowbotham recruited the Bedford Level, a 9.7 km (6 mile) section of the Old Bedford River. The latter is an artificial river formed by a partial diversion of the River Great Ouse in the Fens, Cambridgeshire, intended to reduce flooding of the fenlands. It is named after Francis Russell, Fourth Earl of Bedford, who began the project in 1630 although it was not completed in his lifetime. The Bedford Level is an uninterrupted stretch which runs in a straight line to the north-east of the village of Welney.

Rowbotham’s idea was to set up a telescope 20 cm (8 inches) above the surface of the water at one end of the Bedford Level and use this to watch while a boat was rowed towards Welney Bridge at the other end, six miles away. The boat had a flag on three-foot (0.91 m) mast. If the Earth really was curved, the top of the mast would disappear long before the boat reached Welney Bridge. Rowbotham relied on an approximation used by surveyors: the drop expressed in inches is 8 times the square of the distance in miles. After one mile the drop is eight inches; after two it is 32 inches; and after three it is 72 inches or six feet.

This approximation holds good for the distances involved, but it fails to take account of the height above the ground of the observer. A more accurate calculation shows that the portion of the boat hidden from Rowbotham’s view would be zero after a mile, 8 inches (0.2 m) after two miles, and 2 ft 8 inches (0.81 m) after three miles. Nevertheless, only the top of the mast would be visible at three miles, and long before it reached Welney Bridge the whole of the boat would have disappeared. Instead, it remained completely visible throughout its journey, which Rowbotham took as proof that the Earth is flat.

Based on his observations, Rowbotham published a pamphlet entitled Zetetic Astronomy, which he expanded into the book Earth Not a Globe in 1865. He suggested that the Earth is a flat disc with its centre at the North Pole, and that it is surrounded by a wall of ice. The Sun and Moon were located 3,000 miles (4,800 km) above Earth, and the stars and planets were a further 100 miles (160 km) away.

But Rowbotham had made an elementary mistake. He had failed to realise that the effects atmospheric refraction close to the water can cancel out the effect of curvature, making the Earth’s surface appear flat or even concave. The same effect can make the Sun appear above the horizon shortly before it actually rises, or after it has set. The phenomenon was well known in Rowbotham’s day, and it was routinely allowed for by sailors navigating at sea, and by surveyors.

Rowbotham’s views understandably attracted very little attention until 1870, when a supporter by the name of John Hampden (unrelated to the Civil War-era politician) wagered £500 that that nobody could repeat the experiment and show that the Earth was other than flat. The challenge was taken up by none other than Alfred Russel Wallace, co-proposer of the theory of evolution by natural selection. Wallace’s day job was a surveyor, and he would have known how to avoid the pitfalls that had affected the original experiment albeit he was apparently unaware of Rowbotham’s efforts. £500 was a considerable sum of money at the time (over £50,000 at today’s rates) and Wallace doubtless saw it as an opportunity to make some easy money. With the benefit of hindsight, perhaps he shouldn’t have.

Wallace noted that the parapet of Welney Bridge was 4 m (13 ft. 3 in.) above the water but that the Old Bedford Bridge, at the other end of the Bedford Level, was somewhat higher. To this bridge he affixed a calico sheet with a black stripe, which he positioned so that the lower edge of the stripe was also 4 m (13 ft. 3 in.) above the water. The centre of the stripe would be as high as the line of site as a telescope he set up Welney Bridge. Midway between the two bridges he set up a long pole with two red discs attached, the upper one having its centre the same height above the water as the centre of the black band and of the telescope, while the lower disc was four feet below it. The telescope, upper disc, and black band were thus all the same height above the water; the greater height than that of the earlier experiment would reduce the effects of atmospheric refraction. If the Earth was flat, the upper disc as viewed through the telescope would appear level with the black band. If on the other hand the Earth was round the upper disk would appear above the black band.

To ensure fair play, John Henry Walsh, editor of The Field magazine, was appointed as an independent referee. Walsh was a good choice, as he was not personally acquainted with either Hampden or Wallace. He also had prior experience deciding wagers. But shortly after funds were lodged with Walsh to guarantee the wager, Hampden demanded a referee of his own. Wallace was agreeable, but Hampden chose fellow flat earth enthusiast William Carpenter. Furthermore, Walsh was unable to remain at the Bedford Level for the whole duration of the experiments and a surgeon named Martin Wales Bedell Coulcher stood in for him as Wallace’s referee.

As might be expected, the experiments showed the upper disk apparently raised above the Old Bedford Bridge marker. Coulcher sketched the view through the telescope, and Carpenter signed it to affirm that this was what both men had seen.

Then things started to go awry. Carpenter declared that the result did not prove that the Earth was round because the telescope had not been levelled and did not have cross-hairs. Wallace obtained a spirit level and a smaller telescope equipped with cross-hairs, and then performed the experiment again. The outcome, of course, was exactly the same as before. Both referees then sketched what was seen in the second telescope, and Coulcher signed the sketches. But now Carpenter refused to accept the result because the distant marker appeared below the middle one as far as the middle one did below the cross-hair, which he claimed proved that the three were in a straight line, and that consequently the earth was flat.

Hampden eventually agreed to allow Walsh to review the results and make a decision. Both sides submitted reports, and after considering these Walsh ruled in Wallace’s favour and published the reports and his conclusions in The Field. Ignoring Hampden’s protests, he awarded the £500 wager to Wallace.

At this point, things got decidedly ugly. Hampden went to court to get his money back and won because at this stage it was still in the hands of Walsh and had not yet been paid to Wallace. He published a pamphlet alleging that Wallace had cheated and not content with that, he wrote Wallace’s wife Annie threatening to kill her husband. The death threats landed Hampden in jail for three months. Early in 1871, Wallace sued for defamation and was awarded £600. But Hampden transferred all his assets to his son-in-law and claimed he could not pay. Wallace was left having to pay the court costs. The row continued for another twenty years, during which Hampden was twice imprisoned for defamation. It was only brought to and end by Hampden’s death in 1891.

The whole affair left Wallace significantly out of pocket. He had not been a wealthy man before the wager not least of all because his financial acumen fell rather short of his abilities as a scientist. As a result, he struggled financially until 1881, when he was awarded a £200 p.a. pension thanks to the lobbying of Charles Darwin. Wallace was also criticised for becoming involved with a wager to ‘decide’ an issue which had long been an established scientific fact. All in all, it was a thoroughly unpleasant episode in the life of one of the greatest scientists and thinkers of the nineteenth century.

In 1901, Henry Yule Oldham, a lecturer in geography at King’s College, Cambridge, repeated the Bedford Level experiment using three poles fixed at equal height above the water level, which he viewed with a theodolite and a plate camera. Oldham’s version of the Bedford Level experiment was regarded as definitive because of the photographic evidence. He presented his results in a lecture at the British Association for the Advancement of Science, and they were taught in schools for many years until the first photographs taken from space became available in the late 1940s.

As is often the way with what the late Sir Patrick Moore once described as ‘independent thinkers’, the Flat Earthers were not about to give up. In 1904 Lady Elizabeth Anne Blount hired photographer Edgar Clifton to use a camera equipped with telephoto lens to take a picture from Welney Bridge of a large white sheet touching the surface of river six miles (9.7 km) away, at the position Rowbotham had conducted his original experiment. The camera was mounted two feet above the water, and Clifton was able to obtain a picture of the target, which should have not have been visible. The experiment, of course, suffered from the same vulnerability to atmospheric refraction as had the original. Needless to say, this did not stop Lady Blount from publishing the pictures far and wide.

To this day, Flat Earth enthusiasts continue to champion the Bedford Level experiments as having proved that the Earth is flat. A search on Youtube will reveal an attempt in 2016 to recreate the Rowbotham’s original experiment using a laser pointer mounted on the rear deck of a kayak. Problems faced by the researchers included the discovery that the kayak deck sloped upwards and ‘best judgment’ had to be applied to place the laser ‘as level as possible’. The video has received 1,600 ‘likes’ against 805 ‘dislikes’, but many of the 2,404 comments posted are unfavourable.

It would be a worthwhile project – possibly for a science ‘outreach’ group – to repeat the Bedford Level experiment with modern equipment. In the meantime, anybody who seriously believes that the Earth is flat is urged to take a look at this spectacular video of the Turning Torso building in Malmo, viewed from successively greater distances on the Danish side of the Øresund strait between Denmark and Sweden.