It is popularly thought that the concept of a round earth is a principle that was hard-won by science in the face of stiff opposition.
There is a well-known image of Christopher Columbus (1451-1506) holding up an egg to illustrate the roundness of the earth to sceptical on-lookers. However, the truth is that most educated people since the days of the Greeks were convinced that the world is round.
It is said that Pythagoras was the first to suggest that the earth is round about 525 BC. The suggestion was made on philosophical grounds - the sphere was considered to be the perfect shape.
Later, Aristotle marshalled convincing evidence that the earth is round. He noted that as one travelled north or south while observing the night sky, visible stars disappeared beneath the horizons behind and new stars appeared over that horizon ahead. He also noted that when ships sailed out to sea, regardless of the direction, they always disappeared from sight hull first.
On the other hand, ships heading towards land always showed their masts first as they came over the horizon. Aristotle also noticed that the earth's shadow on the moon during a lunar eclipse was always a circle, regardless of the position of the moon. All of these observations could be explained only by assuming that the earth was a sphere.
Christopher Columbus believed the earth is round and this theory was not seriously criticised by scholars of the day. Based on his studies, Columbus decided that the earth was 25 per cent smaller than previously thought, and on this basis he concluded that Asia could be reached quickly by sailing west.
He estimated that Japan lay 2,700 miles west of the Canary Islands. The correct figure is 13,600 miles, more than five times farther. If the Americas had not crossed Columbus's path he would probably have sailed off into oblivion.
The idea of a rotating earth was much less easily established. The Greek philosopher Heraclides of Pontus suggested in 350 BC that the earth rotates on its axis but most ancient and medieval scholars refused to accept this idea.
The Copernican model of the solar system (1543), in which the earth revolves around the sun, made the idea of a non-spinning earth illogical, and slowly the notion that the earth rotates on its axis was accepted by all. However, it was not until 1851 that the earth's rotation was experimentally demonstrated by the French physicist Jean Bernard Leon Foucault (1819-1868).
Foucault swung a huge pendulum (28 kg iron ball suspended on a 60 metre wire) from a church dome in Paris. The upper support restrained the wire only in the vertical direction and the ball was set swinging in a plane, with no lateral or circular motion. The physicists had concluded that such a pendulum would maintain its swing in a fixed plane regardless of the earth's rotation. Therefore, such a pendulum at the North Pole would swing in a fixed plane while the earth fully rotated counter-clockwise under it in 24 hours.
A person at the North Pole watching the pendulum would be carried with the rotating earth, which would seem motionless, and the plane of the pendulum swing would seem to turn clockwise through a full revolution every 24 hours. The same thing would happen at the South Pole except the plane of the swing would seem to turn counter-clockwise.
At latitudes below the poles, the plane of the pendulum swing still turns relative to the earth but to lesser and lesser extents as you move further from the poles. The plane of the pendulum swing relative to the earth at the equator does not alter at all. Foucault's 1851 experiment showed that the pendulum's plane of swing relative to the earth turned in the proper direction and at just the proper speed. One could "see" the earth turn under it.
The surface of the spinning earth moves fastest at the equator. In 24 hours it makes a circle of 25,000 miles at a speed of a little over 1,000 miles per hour. As you travel north or south from the equator, any spot on the earth's surface travels more slowly since it need complete only a smaller circle in 24 hours. At the poles of the earth the surface is stationary.
The air over the surface of the earth moves along with the earth's rotation. Therefore, if air moves northwards or southwards from the equator it will be rotating faster than the surface over which it moves and it will veer into a clockwise twist in the northern hemisphere and into a counter-clockwise twist in the southern hemisphere. These are called cyclonic disturbances and large storms of this type are called hurricanes or typhoons. Smaller, more intense storms are called cyclones or tornadoes. A tornado over the sea can dramatically suck up water into a sea spout.
The earth is not a perfect sphere and Isaac Newton (1642-1727) had already deduced this. He considered the consequences of the fact that the earth's surface rotates at different speeds at different latitudes. This means that the centrifugal forces acting on the earth vary with latitude. Centrifugal force tends to push material away from the centre of rotation.
When your washing machine drum goes into rapid-spin the washing that had previously distributed itself throughout the volume of the drum is now squeezed against the inner wall of the drum by the centrifugal force of the rapid spin. The centrifugal effect on the spinning earth increases steadily from zero at the poles to a maximum at the rapidly moving equatorial belt. Therefore the earth should naturally be pushed out into a bulge around its middle. Theoretically, the earth should be an oblate spheroid with an equatorial bulge and flattened poles. And this is true - the earth is shaped more like a tangerine than a football. Newton calculated that the flattening of the poles should be about one over 230 times the total diameter of the earth, which is close to the truth.
William Reville is a senior lecturer in biochemistry and director of microscopy at UCC