Could a simple experiment have saved the Ancients as well as the Christian Church a lot of existential bother?
So-called Foucault's pendulum, courtesy of our friends in 'The Other Place'.
One of the great issues in the long-running battle between science and commonsense, is the queston of whether the Earth moves - or if it is motionless and everything else - moon, stars, other planets - moves around it. The idea that the Earth must be fixed motionless at the centre of all things (not even allowed to rattle around on its axis every day) was demonstrated so compellingly by Aristotle that was not only accepted but much more - became uncontroversial. This despite the fact that Aristarchus of Samos (in the third century BCE) had already offered the alernative explanation for the observed motion of the heavenly objects by proposing that the earth turned on its own axis and travelled around the sun.
But Aristotle persuaded Hipparchus (second century BCE) and, above all, Ptolemy (second century AD) to reject this explanation with several powerful arguments. First, you can't feel the rotation of the earth. Second, a ball thrown vertically upwards back to exactly where it started - it is not deflected slightly to one side. And finally, look as hard as you like, you cannot observe any changes - even over the full period of the Earth's 'supposed' orbit of the Sun - in the relative position of the stars. That is, not without powerful telescopes, of the kind that did not exist until long after Galileo and Copernicus. The Earth-centred view satisfied the most scrupulous investigators for two thousand years. And of course it also satisfied the Christian Church, who found in it an agreeable echo of the Genesis story in the Bible.
As everyone knows, Copernicus and Galileo changed the consensus on the correct arrangement of the universe, but curiously a simple experiment COULD have demonstrated that elusive movment of the Earth long before.
How can one measure such a slow rotation? In 1851, a French astonomer and physicist, Jean-Bernard-Leon Foucault, suspended a 67 metre, 28 kilogram pendulum from the dome of the Pantheon in Paris. The plane of its motion, with respect to the earth, rotated very slowly clockwise. This shift is most simply explained if the Earth turns.
Image credit
The animated image was created by Dominique Toussaint for Wikipedia Commons, it was their 'image du jour' in November 2007. Curiously though, it has been expunged from the English Wikipedia page on the Pendulum. That's editing for you! (Maybe someone thought the compass points should have had a 'E' somewhere...)
