Heisenberg and the early days of quantum mechanics (1976) [pdf]
cs.westminstercollege.edu
cs.westminstercollege.edu
He was attempting to formalize de Broglie's "particles as waves" concept, which, according to the article, "could obtain the quantization rules of Niels Bohr and Sommerfeld by demanding that an integer number of waves should be fitted along a stationary orbit."
Schrödinger's equation put that claim on firm mathematical grounds. It gave correct predictions. But just what this new "wave function" was remained up to interpretation.
Is the article available as a regular web page anywhere (i.e. not a pdf?) - if so, we can change it again.
I haven't verified that it's correct (there are a few benign artifacts at the very least), but it looks right content-wise