Atomic Models and X-Ray Spectra

Abstract

IN the recent discussion in NATURE on the constitution of the atom, attention has been directed mainly to the electrostatic forces exerted by the positively charged portion of the atom. Prof. Nicholson has been successful in calculating the frequencies of the lines in the nebular and coronal spectra on this basis by employing Rutherford's model atom consisting-of a central nucleus surrounded by a ring (or rings) of electrons. Bohr's theory, though not dependent on the usual dynamical laws, involves the calculation by ordinary mechanics of the steady motion of the electron in the electrostatic field of the positive nucleus. In the case of a simple nucleus this procedure leads to results as to the frequencies that agree with observation. It may, however, be necessary to suppose, at least in the case of the heavier atoms, that the nucleus produces not only an electrostatic but also a magnetic field. Such a view has recently been developed by Prof. Conway using the atomic model of Sir J. J. Thomson. If we adopt Rutherford's model the expulsion of α and β particles from radio-active substances with large velocities may indicate that the particles possess these velocities within the nucleus. If they are in orbital motion a magnetic field would exist outside the nucleus.1 This hypothesis may be associated with the theory of the Zeeman effect put forward by Ritz, and also with the theories of magnetic action developed by Langevin and by Weiss. According to the latter, there exists an elementary magnet, the magneton, which is common to the atom of a large number of different substances.