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First edition, author's presentation offprint, of Bohr's explanation of the Stark and Zeeman effects, the splitting of spectral lines when an atom is placed in an electric or magnetic field. "On the 20th of [November 1913] Stark announced to the Prussian Academy of Sciences an important new discovery: when atomic hydrogen is exposed to a static electric field its spectral lines split, the amount of splitting being proportional to the field strength (the linear Stark effect). After Rutherford read this news in Nature, he at once wrote to Bohr: 'I think it is rather up to you at the present time to write something on . . . electric effects" (Pais, Niels Bohr's Times, 182). "Bohr's analysis of the Stark effect appeared in the Marsh issue of Philosophical Magazine, which also included a first attempt to explain the Zeeman effect on the basis of the theory. Bohr reasoned that an external electric field would deform the circular orbits of the electrons but not influence the transition mechanism between stationary states. Restricting his analysis to large quantum numbers and making use of a correspondence argument he found that, theoretically, the hydrogen lines would separate into four components. But in reality only two symmetric components would turn up, for otherwise one could not 'obtain the continuity necessary for a connection with ordinary electrodynamics' . . . By the spring of 1914 Bohr was confident that his theory agreed with, or could be developed to agree with, the Stark effect . . . Sommerfeld's growing interest in the Bohr atom was in part indebted to the Stark effect and its relation to Bohr's theory, a subject he dealt with in a Munich colloquium of 27 May 1914. A few days later he wrote in a letter to the French physicist Paul Langevin, this time relating to the Zeeman effect, that 'in the atom an unsuspected number-theoretical symmetry and harmony appears to rule, as from another side Bohr has shown'" (Kragh, Niels Bohr and the Quantum Atom, p. 129). Although the present paper played an important role in gaining acceptance for the radical new atomic theory Bohr had proposed in 'On the constitution of atoms and molecules,' the available method of quantization was too restricted to permit a complete explanation of the Stark effect. It turned out that only hydrogen exhibits a linear Stark effect, a fact which could not be fully understood until the introduction of parity in quantum mechanics. Furthermore, hydrogen and all other atoms exhibit quadratic (and higher) Stark effects, proportional to the square (and higher powers) of the electric field strength, but their proper treatment can only be given in terms of quantum mechanics. 8vo, pp. [1], 506-524. Original printed wrappers (dust-stained at edges, a few small chips, glue residue at spine). Seller Inventory # ABE-1595592763854
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