P. Lenard On the Principle of Relativity, Ether, Gravitation

P. Lenard On the Principle of Relativity, Ether, Gravitation, 1920, Hirzel Verlag.

P. Lenard’s brochure is a series of remarks concerning the general principle of relativity of A. Einstein. The remarks scarcely touch upon the essence of the principle, and mainly address the broad generalizations—extrapolations—and overly hasty “consequences” of Einstein’s theory. While fully reconciling himself with the old “special” principle of relativity, which mathematically precisely describes the results of experiment in the domain of rectilinear uniform motions, Lenard protests above all against the universality of the new principle, restricting its applicability to the domain of motions occurring under the action of forces proportional to the masses (for example, gravitation). In such motions the effects of inertia disappear; in all other cases of motion, however, the effects of inertia make it possible to establish absolutely the presence of nonuniform motion. Lenard proposes to call Einstein’s new theory the “extended principle of relativity,” or the “gravitational principle.” Lenard’s second remark concerns the “elimination” of the concept of the world ether from physics—as a consequence of Einstein’s principle. Lenard considers this “elimination” a simple misunderstanding. In establishing the duality of scientific conceptions of nature, expressed either in the purely mathematical description of phenomena, or in the construction

¹ Cf., for example, A. Sommerfeld, Atombau, p. 380, 1921, where the author apologizes for using the term “ether.”

mental models of the same phenomena, Lenard points out that in the mathematical method the ether was eliminated long before Einstein, or rather did not even appear there; and if it did figure there at times, then purely externally, as a simple mathematical notation. On the other hand, the rejection of the ether in the method of models is obviously equivalent to the rejection of the method itself. Such a consequence, however, can hardly be derived from the principle of relativity, even from the general one. Lenard ironically remarks that many properties of the world ether appear quite clearly in Einstein’s four-dimensional space of variable curvature.

In the third part of his article Lenard points to the possibility of constructing an electromagnetic theory of gravitation, proceeding from the conception of a discontinuous ether consisting of particles moving with the speed of light. The theory is sketched by Lenard only in the most general outlines and is not entirely clear. The fundamental propositions are as follows: 1) matter is constructed of rotating elements (dynamids), 2) two dynamids act upon one another like two circular currents, 3) the planes of rotation of these currents can always turn, 4) the magnetic field of the elementary circular currents does not fill space continuously, but is discontinuous in space and in time. The author also describes a model of his dynamids, demonstrated at the physical seminar in Heidelberg.

S. Vavilov.