Buridan's argument

[pc]

Dear James,

I have just finished "God's Philosophers" and I have enjoyed it immensely. I have one point of correction. Buridan's argument that the earth's rotation could be proven by firing an arrow straight up does in fact work, but the implementation of the concept was insufficient. The Foucault pendulum, as well as corrections on ballistic trajectories for the Coriolis effect are exactly the phenomenon that Buridan predicted. Concerning the great wind that would presumably arise because of the earth's rotation, there is such an effect. Hadley cells would produce a north-south circulation of air in the absence of rotation, but the earth's rotation to the east produces an apparent westward component to the wind at the earth's surface which we know as the trade winds.

PC

[James Hannam]

Hi PC,

Thank you for your message and kind words. I'm very glad you enjoyed the book. Sorry for the late reply, but I've not been doing much on line over the Easter break.

Buridan was right to say that you should see some effects of the Earth's rotation. But he was wrong about how pronounced those effects should be. I think we need to be very careful before we say that someone is right when they hit on something that later turns out to be correct in a way they didn't really expect. The more important point, in my opinion, is that Buridan was being sensible in what he suggested.

Best wishes

James

[jonkon]

PC's point is well taken, but assuming that the release of the arrow can be sufficiently controlled to detect the rotation of the earth - a possible topic for The Discovery Channel's Myth Busters - I question whether Buridan would recognize the significance of the resulting trajectory. Despite its fundamental and practical importance in aiming cannon, the complex trajectory of a cannon ball was not correctly described and resolved into its uniform horizontal and accelerated vertical motion for another 250 years. Bradwardine's earlier introduction of the exponential function for a mathematical description of motion was to resolve a logical contradiction in Aristotle's treatment of motion and did not attempt to accurately describe the actual motion of an object.