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McGill, 1905

Narrator: ``So the theorists are working on it, and surely with a little more mathematical sophistication all these temporary fixits will reveal their sensible character. Sadly, the experimentalists are at it again too, and are generating more embarrassing problems. In a quaint backwater town of the snowy Canadian wilderness, Ernest Rutherford is visiting McGill University and tinkering with Marie Curie's alpha rays.''

Rutherford: ``It's amazing how many of these heavy elements decompose spontaneously, giving off alpha particles, which I have discovered are actually the nuclei of helium atoms.''

``I believe I'll move back to England to do some more experiments with these things.''

[Walks across stage to signify this.]

``Here in Manchester I tried scattering alphas off a thin gold foil.

[Uses chalk in demo of scattering.]

`Most of the time we see just what you'd expect: the alphas shoot right through the foil and out the other side, with only a little deflection. But occasionally - very rarely - one will bounce straight back from the foil. It is like firing shells at a piece of paper handkerchief and having them bounce back at you.

``The only way this could possibly happen is if most of the mass of the atom is contained in a small, hard, positively charged NUCLEUS about which the electrons orbit like planets about the sun!''

Born: [jumping up and down, ears steaming, foaming at the mouth]

``That's insanity! Orbiting electrons are accelerating and thus radiate away their energy!''

Grabs chalk, draws spiraling orbit; classical calculations show electron falls into nucleus in $\sim 1$ ns.

Bohr: [takes chalk to blackboard]
`` . . . so we're forced to postulate discrete orbits and energy levels in atoms.''


\begin{displaymath}L_n = n \hbar \end{displaymath}


\begin{displaymath}E_n = - {R \over n^2} \end{displaymath}

[Connects all three problems by quantization of angular momentum, thus also emitted and absorbed energy.]


next up previous
Next: The Roaring 20's Up: The Dreams Stuff is Made Of Previous: Swiss patent office, 1905
Jess H. Brewer
2000-01-23