The Science of Discworld IV

the United States. One of his supporters, William Carpenter, published
Theoretical Astronomy Examined and Exposed – Proving the Earth not a Globe
using the pseudonym Common Sense. He followed it with
A Hundred Proofs
the Earth is Not a Globe
. One was the observation that many rivers flow for long distances without descending more than a few feet, an example being the Nile, which drops one foot in a thousand miles. ‘A level expanse of this extent is quite incompatible with the idea of the Earth’s convexity. It is, therefore, a reasonable proof that Earth is not a globe.’
    It pays to check the facts. The Nile is fed from Lake Victoria, although there are other rivers that run into the lake so it is technically not the source. It flows more than 6,500 km to the Mediterranean Sea. The lake is 1,140 metres above sea level. So the river drops, on average, slightly under one metre for every six kilometres of its length. Over a thousand miles, it drops about 900 feet, not one.
    People with extreme religious beliefs, who adopt a human-centred view of the world despite attributing its creation to an all-powerful deity, tend to have problems with universe-centred thinking. Lady Anne Blount was a Biblical literalist, and a rather unimaginative one to boot. Not only did she view the Bible as the sole source of reliable information about nature; she had no doubt that it states that the Earth is flat. Convinced that no true Christian could believe in a round Earth (so much for Augustine), Lady Blount set up a magazine,
Earth not a Globe Review
. In 1901 she founded another, called simply
Earth
.
    That was the year when the geographer Henry Yule Oldham repeated the Bedford Level Experiment using a better experimental design. He placed three vertical poles in the river, at the same height above the water. When viewed through a theodolite, the middle pole was almost three feet above the other two, a result that is consistent with a round Earth of the correct diameter. Until the Earthrise photo became available, this experiment was widely taught in schools to demonstrate that the world is round. Lady Blount’s response was to hire a photographer, Edgar Clifton. In 1904, using a telephoto lens placed two feet above the river, he took a picture looking back from Welney bridge to where Rowbotham had started it all by wading intothe river, six miles distant. The photo showed a large white sheet, touching the surface of the water. Apparently the result surprised him: he knew the sheet should not have been visible. Lady Blount gave the picture a lot of publicity.
    How did Clifton get his photo? Was it a fraud? That would be easy to arrange. Take the photo from much closer, then switch plates when performing the actual experiment in the public eye. Or place the sheet or camera higher than claimed. Alternatively, Lady Blount might have got lucky: the result could have been a mirage. Temperature differences in air bend light, in ways that depend on which regions are hotter and which colder. A ‘superior image’ mirage would have led to similar results.
    Even in these allegedly enlightened times, belief in a flat Earth survives, remarkably unaffected by a wealth of contrary evidence, though it is definitely a minority view. The
International Flat Earth Research Society
, usually referred to as the
Flat Earth Society
, was set up in 1956. The Society’s most recent proposal for the shape of the Earth is a disc centred at the North Pole, surrounded by a 150-foot wall of ice at its rim (Antarctica). As evidence, the Society cites the logo of the United Nations, which depicts exactly this arrangement except for the ice wall. The logo is based on an azimuthal equidistant projection centred on the North Pole, which is one standard mapmaking method for turning a round Earth into a flat map.
    Given the attitudes of the religious right and other pressure groups in America to issues like evolution and climate change, and Young Earth Creationism – which believes that the Bible proves the Earth is at most 10,000 years old fn4 – it wouldn’t be a great surprise to read intomorrow’s papers that some school board in Boondocks Mississippi is insisting that science lessons should ‘teach the controversy’ about the shape of our world, by giving equal time to the proposition that it’s flat.
    We now come to the most curious twist in the story of the Bedford Level Experiment. A few years earlier, in 1896, the American newspaper editor