In 1851, French scientist Leon Foucault (1819 - 1868), with a simple pendulum, finally showed the earth rotated. - by guest blogger John Faulkner

The motto of the Royal Society is - Nullius in Verba (take nobody's word for it).....

Drop an object and it falls toward the ground, the earth seems fixed where it is. The skies, stars moon, planets and sun, move overhead. Aristotle said this proves the earth was the centre of the universe with the heavens revolving around it.

Over time, philosophers suspected the earth might be rotating on its own axis. Copernicus showed that the Earth orbited the sun and his solution to the moving skies was a rotating Earth. Galileo with his telescope saw that Jupiter spun on its own axis, so why not the earth? Newton discovered gravity, which explained, if the earth rotated (at up to 1000mph at the equator) everything did not fly off into space.

But there was no evidence the earth moved and Egyptian philosopher Ptolemy (100AD), had proposed the earth sat within moving crystal spheres that held the skies. Nobody could disprove it.

In 1851 French scientist Leon Foucault (1819 - 1868), with a simple pendulum, finally showed the earth rotated.

Foucault knew that Newtons First Law of motion means a moving object would continue unless another force acted upon it. Setting a pendulum swinging on a wire, enough to resist forces other than gravity, the pendulum would continue in its plane. Foucault hung a 67 meter long 28 kilogram pendulum from the dome of the Pantheon in Paris running North to South. The pendulum gradually appeared to shift direction but since no new forces were acting on it this  must be that the Earth was moving underneath! Foucault worked out that the formula to calculate the degrees of shift as follows....

Degrees shift per day  = 360 multiplied by the sine of the pendulums latitude on the earth.

So...

at the north pole where latitude is 90 degrees (the sine of 90 = 1) the shift is 360 degrees/ day

at the equator where latitude is 0 degrees (the sine of 0 = 0) the shift is 0 degrees/ day

Surrey SATRO office latitude is 51.24 degrees (the sine of 51.24 = 0.8276) the shift is 298 degrees/ day

Foucault went on to develop a better, more convenient instrument to demonstrate this effect - the gyroscope.

Thanks to him the search to find if the earth moved resulted with a device found in many objects that need to know orientation. Here are some examples.... ship stabilisers, aircraft autopilots, non magnetic compasses for navigation, virtual reality headsets, robotics, Segway Scooters....

                                                                                                             - John Faulkner