Published online by Cambridge University Press: 24 October 2008
There exists a group of action functions, depending on a parameter γ giving for every γ ≥ 0 a static solution with central symmetry and finite energy, both for the electric and magnetic field, and going over into Maxwell's action function for weak fields. For γ = 1 we obtain Born's case distinguished by a perfect symmetry between electric and magnetic field. For γ = 0 the action function takes a particularly simple form and the comparison with the results of Heisenberg, Euler and Kockel allows of an approximate determination of the fine structure constant.
† Born, , Proc. Roy. Soc. A, 143 (1934), 144.CrossRefGoogle ScholarBorn, and Infeld, , Proc. Roy. Soc. A, 144 (1934), 425;CrossRefGoogle Scholar 147 (1934), 522; 150 (1935), 141.
‡ Infeld, , Proc. Camb. Phil. Soc. 32 (1936), 127,CrossRefGoogle Scholar quoted here as I.
§ p *kl,f *kl are dual to p kl, f kl.
∥ This will be done later in a separate paper written in collaboration with B. Hoffmann.
† The dependence of T on F, P, and not on F, P, R, does not form a restriction, since R can always be expressed as a function of F and P, viz. R 2 = − PF. These assumptions simplify the calculations but are not more special than those in I. There is another generalization, where T depends also on G and Q (cp. Proc. Roy. Soc. A, 144, 425Google Scholar), but we shall not consider it in this paper.
‡ We can safely assume here and later that R ≠ 0, since R = 0 leads to the exceptional case F = P = 0.
† The condition is: Hr 3 = 0 for r = ∞.
† Heisenberg, and Euler, , Zeits. für Phys. 98 (1936), 714;CrossRefGoogle ScholarEuler, and Kockel, , Naturwiss. 23 (1935), 246.CrossRefGoogle Scholar
‡ We omitted in (6·7) the term proportional to (which occurs in the formula of Euler and Kockel) since it arises from the dependency of L on the invariant which we did not assume.