## On the Effect of Electric and Magnetic Fields on Spectral Lines, Offprint issue from the Philosophical Magazine, March 1914, London: Taylor & Francis

London: Taylor and Francis, 1914. 1st Edition. FIRST EDITION, OFFPRINT PRESENTATION ISSUE of Bohr's pivotal 1914 paper. An important test of Bohr's new model of the atom, the quantum theory he began to develop in his revolutionary 1913 'On the Constitution of Atoms and Molecules;' as well, this paper is a significant and necessary bridge between Bohr's 1913 break with classical physics and his later correspondence principle stating that the behavior of quantum mechanical systems must give the same results as classical physics in the limit of large quantum numbers. The 1914 paper offered stands directly between classical and quantum theory and signifies Bohr's own path from one understanding of the universe to another.

Offprint bears Bohr's personal stamp 'Fran Forfatteren' or 'From the Author.' W. P. Watson Antiquarian Books verifies that this was Bohr's own stamp. Beneath the stamp is written 'From the Author,' but I suspect that was written later and by another hand as a translation of Bohr's stamp.

Bohr's 1913 work "postulated the existence of stationary states of an atomic system whose behavior could be described using classical mechanics while the transition of the system from one stationary state to another would represent a non-classical process accompanied by emission or absorption of one quantum of homogeneous radiation, the frequency of which was related to its energy by Planck's equation" (Norman). "The dynamics of Bohr's [1913] atomic models is a manifest departure from classical dynamics, where every acceleration produces radiation. This departure consists of the fact that Bohr's electron does not radiate as long as it describes a stationary trajectory, but only when it jumps from one stationary trajector to another" (Dugas, A History, 547).

Concurrently, Johannes Stark discovered the splitting of spectral lines in strong electrical fields, defying classical explanation. Bohr, however, realized that his new model offered an explanation. In this 1914 paper, then, Bohr wanted to establish "a certain connection between this dynamics and ordinary electromagnetic theory" (Norman). Specifically, he wanted to ascertain whether or not his new theory could account for the variations of spectral lines when atoms were submitted to electric fields (Stark effect) and magnetic fields (Zeeman effect).

Bohr's research "claimed that an electric field would deform the circular orbits of his atomic model so that only two rectilinear motions through the nucleus remained, parallel and antiparallel to the field" (Kox, The discovery of the Stark effect" in AdP 525). He was able to calculate a frequency shift due to an external electric field that agreed with Stark's observations. Bohr concluded that "it seems possible to account for some of the general features of the effect of magnetic and electric fields on spectral lines discovered by Zeemann and Stark" (Bohr). His conclusion would, in time, lead directly to his own correspondence principle, a cornerstone in the quantum mechanics soon to be formulated by Heisenberg and Schrödinger.

Bohr's correspondence principle which states "that the behavior of systems described by the theory of quantum mechanics (or by the old quantum theory) reproduced classical physics in the limit of large quantum numbers. In other words, it says that for large orbits and for large energies, quantum calculations must agree with classical calculations" (Wikipedia). Item #451

CONDITION & DETAILS: London: Taylor & Francis. Offprint issue, original wraps. Very small stamp at the foot of p. 506. Octavo (8.75 x 5.5 inches; 219 x 138mm), pp. 506-525. Bears Bohr's personal stamp "Fra Forfatteren" or "From the Author." W. P. Watson Antiquarian Books verifies that this was Bohr's own stamp. Beneath the stamp is written "From the Author," but I suspect that was written later and by another hand as a translation of Bohr's stamp. Small chip at head of spine and foot of front wrap. Clean and bright throughout. Very good condition.

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Price:
$1,400.00
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