The cosmos loves irony. While trying to prove that the Earth is fixed in space, an Italian priest described something similar to the Coriolis effect – the slight deflection experienced by objects moving in a rotating frame of reference – nearly 200 years before mathematician Gustave Coriolis worked it out in 1835.
In 1651, Giovanni Riccioli published 77 arguments against the idea that the apparent motions of the heavens were due to the Earth’s rotation and orbit around the sun. These included claims that Hell would be in the wrong place, aesthetic concerns over proportion and harmony, and more scientific approaches.
Now, Christopher Graney at Jefferson Community and Technical College in Louisville, Kentucky, has translated them from Latin, and discovered that Riccioli conjectured phenomena resembling the Coriolis effect (arxiv.org/abs/1012.3642).
Riccioli argued that if the Earth were rotating, the speed of the ground at different latitudes would be different, so cannon shots fired due north or south from near the equator would show a slight deflection east or west as the ground moved beneath them during flight. No such effect was known at the time, so he wrongly concluded that the Earth must be stationary.
In reality, the Coriolis effect is subtle, noticeable mainly in large-scale systems such as weather patterns and ocean currents.
Graney says that Riccioli is often ignored because of his anti-Copernican stance, but in the absence of more precise measurements, he says his reasoning in this case was sound. “Judging from the knowledge of the time, it was a pretty good argument,” says Graney.
Still, historian Owen Gingerich, formerly of Harvard University, says Coriolis should retain credit for the idea because he recognised that – except for shots fired exactly on the equator – the deflection should occur for objects moving in any direction, not just north or south. “It shouldn’t be confused with the genuine Coriolis force,” Gingerich told New Scientist.