17th century priest discovered the Coriolis effect while trying to disprove Copernicus

Even the fiercest opponents of science can sometimes make brilliant discoveries...just not quite in the way that they intended. Like Italian priest Giovanni Riccioli, who in his zeal to prove Copernicus wrong unintentionally discovered the Coriolis effect 200 years early.

In 1651, over a hundred years after Nicolaus Copernicus's On the Revolutions of the Celestial Spheres showed that Earth is not the unmoving center of the universe, Giovanni Riccioli offered a furious rebuttal composed of 77 different arguments. Some were theological - if the Earth moved, then this apparently meant Hell would end up in the wrong place, which was obviously ridiculous - and some were aesthetic considerations of cosmic harmony and balance, and how a changing Earth ruined all that.

But some of his arguments were along more scientific lines. Riccioli maintained that, if Earth really was rotating, then the ground is moving at different speeds depending on what the line of latitude is. He wrote that a cannon placed near the equator and fired due north or due south should show a slight deflection east or west in the curve of the cannonball. This, he said, would be caused by the Earth turning beneath the fired cannonball. But, since cannonballs don't move like that, he concluded, the Earth must not move.

It was a very nifty bit of reasoning, and completely correct except for one tiny detail - cannonballs do move like that, and the Earth does indeed move. Quite by accident, he had described more or less the same effect that Gustave Coriolis would demonstrate nearly two centuries later in 1835. Of course, Riccioli's version was just a thought experiment used to prop up an anti-Copernican screed, while Coriolis was actually trying to better understand how the world works.

Indeed, Riccioli can't be given full credit for discovering the entire effect - he figured such an effect would be noticeable only when objects moved due north or due south, but Coriolis demonstrated the effect is apparent for any movement across a sphere. That said, the Coriolis effect is generally a very subtle phenomenon, and often misunderstood - check out our primer for more on what it's all about.

But why have we only learned about Riccioli now? Well, like any good 17th century priest, he wrote exclusively in Latin, and his known anti-Copernican stance meant scientists and historians weren't in any great hurry to translate his ideas. Still, although he was most definitely on the wrong side of the heliocentric debate, his arguments about the non-existence of the Coriolis effect were actually fairly well-reasoned based on what was known in 1651.

So then, a priest writing an anti-scientific screed used surprisingly good science to argue his case, which managed to accidentally discover a key scientific principle two centuries ahead of its time...except he himself dismissed it as nonsense. It just goes to show you - when in doubt about history, assume the most ironic thing imaginable happened.

[arXiv via New Scientist]