Writer Erik Larson (profile here) described it as follows:
“In 1627, a very brave if melodramatic German mathematician, Joseph Furtenbach, aimed a loaded cannon into the sky in preparation for an experiment he hoped would provide the first real-world test of another of Galileo’s theories: that the earth rotated on a fixed axis. This was high-wire science. If Galileo was right — and Furtenbach fervently hoped he was — a cannon ball fired straight into the sky would fall back to earth somewhere to the west of the cannon” —
I didn’t know that, did you? I wouldn’t have thought of it, but I’m not Furtenbach or Galileo.
— “while the earth’s rotation carried Furtenbach safely east. If Galileo was wrong, the ball would fall to earth exactly at the point where it rose from the cannon, and Furtenbach would be dead.”
(Spoiler alert: Wikipedia says here Furtenbach lived from 1591 to 1667, i.e. he was around for another 40 years after this demonstration.)
“He fired the cannon. As the ball soared into the sky, he hurried to the muzzle and sat on it. Skeptics in the audience no doubt stepped back a respectful distance, wary not only of the descending ball but also of the likely splash of viscera.”
I think Larson’s being a little speculative here, but it’s what I would do in similar circumstances.
“How the seconds must have dragged as that ball whined into its descent, the smile on Furtenbach’s face growing fixed, the more squeamish members of the audience raising their hands to cover their eyes but peeking of course through the latticework of fingers. … Thwump. Silence. Furtenbach slid from the muzzle, his head and smile intact. To the west — a small crater. Proof at last. The earth did spin.”
Well, right off, I’m a little suspicious. I mean, how do we know he aimed the cannon straight up, i.e. didn’t cheat by angling it a little to one side? And even if it was, how could the audience tell?
But we know the earth spins, it sorta makes sense, and I know artillerymen compensate for the earth’s rotation. No doubt countless kids have mimicked this experiment throwing a ball up in the air, and probably some of them got hit on the head, but that’s easily attributable to sloppy throwing. Who can throw perfectly straight up? I can’t.
Quoted from Isaac’s Storm, by Erik Larson, Vintage Books edition (1999), pp. 48-49.