BOHR, Niels Henrik David. On the Quantum Theory of Line-Spectra, I-III [all published].
Copenhagen: Bianco Lunos, 1918-1922. All first editions.

Nobel laureate Percy W. Bridgman’s annotated copies. Besides Bohr’s derivation of the Balmer formula (1913) this work, in which he first gave a clear formulation of his ‘correspondence principle’, is by many considered to be his greatest contribution to physics.

Bohr’s correspondence principle (or postulate) states in general that although classical physics is incomplete there must be a fundamental analogy between quantum theory and classical physics. Actually Bohr at first referred to the postulate as the ‘principle of analogy’. It was Bohr’s underlying idea that the new quantum theory must satisfy in the limiting cases, e.g., when frequencies v tend to zero or quantum numbers n→∞, that its predictions approximate those of classical physics. When studying different quantum theoretic problems one can thus utilize already established facts from what classical physics predicts in that particular situation, and then work backwards to arrive at new quantum theoretic rules for the system. In this major paper, of which the two first parts were published in 1918 and the third in 1922, Bohr penetrated far into the quantum theory of line-spectra of the Hydrogen atom, and other elements, by using his principle and the classical theory of electrodynamics. Bohr’s method was the principle guide to the progress of the old quantum theory during the early twenties, until it was finally built into the foundation of the new quantum mechanics.

The three issues, offered here, are from the library of American physicist and Nobel laureate Percy W. Bridgman, with his owner’s inscription on the title of all three parts, and with several pages annotated with comments and calculations.

(DSB, XIX, 326:) “Correspondence Principle: It has become increasingly clear that Bohr’s much-misunderstood correspondence principle, a critical component of his work from at least 1918 to 1925, was internally motivated and more robust than the loose heuristic it has often been made out to be. Bohr relied on it for epistemological reasons concerning our ability to infer atomic properties from empirical phenomena such as spectra. His emphasis on this empirical approach over simple hypothesizing can be seen in his justification for his 1913 model via the application of the frequency relation E=hv to the Balmer formula for the hydrogen spectrum. But that method justified claims only about stationary states and transitions between them. To allow investigation of other atomic properties, Bohr looked to mathematical limiting relations in order to set up some sort of correspondence between those properties and the properties of observable emitted radiation. He then used the classical limit as a guide to indicate how observable emitted radiation corresponded to presumed electron motion.
This sense of correspondence is precisely the idea that led to both the unusual Bohr-Kramers-Slater theory and Werner Heisenberg’s quantum mechanics, and it influenced much of Bohr’s later work. The success of classical electrodynamics, especially in spectroscopy, convinced Bohr that something must be vibrating long enough to emit (and therefore correspond to) electromagnetic radiation at precise frequencies. But that meant that the oscillators and radiation were not independently detectable (thus dubbed ‘virtual’), and that they conserved energy only statistically. When energy conservation was shown to hold strictly, Bohr questioned the reality of the oscillators, which helped lay the foundation for Heisenberg’s purely formal use of the classical mechanics of oscillatory motion”.

Three separate issues. 4to: 268 x 214 mm. Original printed wrappers, extremities slightly worn, front wrapper of part 1 with a light water stain, rubber stamp 'Printed in Denmark' at the bottom of all three parts. Published as Fasc. 1-3, no. 1, vol. 4 of the 8th series of 'Mémoires de l'Académie Royale des Sciences et des Lettres de Danemark'. 118 pp.