On the Anniversary of G. A. Lorentz

B. V. Ilyin.

On December 11, 1925, fifty years were completed of the scientific and pedagogical activity of Hendrik Antoon Lorentz, a brilliant representative of modern physics, the creator of the electron theory, and the herald of the theory of relativity.

Professor Lorentz is now 72 years old. He was born in Arnhem, in Holland, on July 18, 1853. After graduating from the university, he took the chair of mathematical physics in Leiden, and he performed these duties until his appointment in recent years to the Taylor Institute in Haarlem. But at the same time, throughout his fifty years of fruitful work, Lorentz has given occasional courses and reports on his investigations not only in Holland, his homeland, but also in Germany, France, England, and America. Lorentz responds vividly to almost all the pressing topics of contemporary physics, contributing to their development all his brilliant talent as an investigator and writer.

Lorentz entered the scientific arena during the flourishing of the mechanistic worldview.

Mechanics, resting on the fundamental laws of Newton as on unshakable rocks, was making its victorious march, rapidly penetrating everywhere and, it seemed, firmly conquering all fields of physics, chemistry, and natural science in general. The astonishing successes of classical Newtonian mechanics in astronomy, which allowed that science to become almost mathematical, were the basis of this triumph of the mechanistic worldview.

Molecular theory, the kinetic theory of gases, already in the works of Bernoulli, of our Lomonosov, appear as the mechanics of molecules, those material bodies of Democritus, possessing a definite diameter, colliding, like billiard balls, according to ordinary mechanical laws.

The “mechanization of heat” was given in the “mechanical theory of heat,” where heat is the “living force” of molecules.

“Molecular physics,” already through the works of Laplace, Poisson, van der Waals, which gave a theory of liquids and of surface phenomena—

tension, was placed on the firm ground of mechanical conceptions.

And so, before Lorentz and in his time, heroic efforts were being made to conquer once and for all the last stronghold—light and electricity.

The bearer of these two forms of energy became the luminiferous ether, at first a hypothetical medium invented only in order to abolish actio in distans, while by the time H. A. Lorentz began his scientific activity this ether had almost the reality of actual matter. Huygens, Fresnel, Cauchy scarcely distinguish the luminiferous ether from real matter. According to their conceptions, the ether too consists of the smallest particles, atoms. Similar conceptions may be found in Maxwell and J. Thomson. Lodge calculates the density of the ether.

With respect to the propagation of light vibrations, the ether in these old theories is regarded as an elastic medium and even, since light vibrations are transverse, as a medium with the properties of a solid body.

But over the course of Lorentz’s scientific activity we see how these simple concrete conceptions gradually have to be complicated, bringing to the foreground the role of the electromagnetic field and of the fundamental constants of the electron theory.

The interpretation of the ether as an elastic continuous medium, and hydrodynamic models of it, despite the attempts of Bjerknes and others, did not provide an explanation of the actual phenomena in optics and electrodynamics.

Gradually the domain of those phenomena which are connected with the electron theory developed and broadened, and they showed definitely that electricity is not an accidental state of matter, but that matter consists of electric charges and that all forces acting both within the atom and molecular forces are of electrical origin.

The fruitfulness of this new “electrical world-view,” the astonishing generalizations in the electrification of molecular forces, and, on the other hand, the contradictions with classical mechanics and electrodynamics connected with radiation (the theory of quanta), and finally the theory of relativity, strongly changed the theoretical foundations of our science.

H. A. Lorentz took the liveliest part in the development of these ideas. In his electron theory he explains all electromagnetic and, consequently, optical phenomena in various liquid and solid bodies by the position, motion, and action of the electrons associated with them.

Lorentz proceeds from the assumption that around each electron there is an electromagnetic field, determined by the equations

Maxwell. The field observed by us in experiments is produced by the superposition of an innumerable multitude of such elementary fields.

The ether penetrates into electrons. In any field the force acting on an electron is composed of electrostatic and electromagnetic forces.

On the basis of these ideas Lorentz obtains his famous law (1880) on the relations of discrete molecules to electric waves in material bodies,

\[ \frac{\mu^2 - 1}{\mu^2 + 1}\cdot \frac{1}{\rho} = \mathrm{Const}, \]

closely connected, according to Maxwell’s electromagnetic theory of light, with the Clausius–Mossotti equation

\[ \frac{K - 1}{K + 2}\cdot \frac{1}{\rho} = \mathrm{Const}. \]

I shall not dwell on the explanation of experiments with the cathode rays of Kaufmann and Thomson, of the effect of magnetization of a light ray (1884), of the thermal conductivity of metals, and so forth. What has been said is already sufficient to form an idea of Lorentz’s ideas in the domain of the theory of electrons.

I pass to the central work of H. A. Lorentz, which made him a precursor of the theory of relativity—to the question of the connection of the electron theory with the propagation of light in material media (1892–1895).

The principal feature of this investigation is the extension of Maxwell’s theory of the electromagnetic field on the basis of the conception of moving ions regarded as sources of the field.

This conception gives Lorentz the possibility of obtaining a correction to dispersion in Fresnel’s theory, which leads to the explanation of the Zeeman phenomenon, discovered later. But the chief result of this brilliant work is the establishment of a definite correspondence between the electrodynamic field of a material system at rest in the ether and the same system carried along with constant velocity. As I have already indicated, Fresnel proceeds from the “stationary ether.”

All bodies, even the terrestrial globe as a whole, are completely permeable to the ether and leave it, in their motion, in perfect rest. This is the theory of the ether at rest. According to this theory, as a consequence of the motion of the earth, in every laboratory connected with the earth the ether, with respect to the earth, ought to possess a certain quite definite velocity of transport (ether wind). Michelson’s famous experiment showed that there is no such ether wind.

There resulted an insoluble contradiction, which was resolved by the contraction theory of H. A. Lorentz, according to which all bodies contract in the direction of their motion in a definite ratio.

This “contraction” theory of Lorentz in essence also contains within itself the formal foundations of the theory of relativity.

Lorentz’s scientific interests are not limited to the capital works on which I have dwelt above. He is attracted by the most diverse subjects. He has produced a number of interesting investigations and important works on the second law of thermodynamics and its relation to the kinetic theory of gases, on Brownian motion, on statistical mechanics, on the propagation of sound, on the interaction of two electrodynamic elements, on dispersion, refraction, on the magnetic influence on the polarization of a light ray, on quantum theory, on gravitation, on the application of the doctrine of indicatrices in the field of gravitation, and a number of others.

Such many-sided scientific and pedagogical work by Professor G. A. Lorentz has created for him an honorable worldwide renown and makes his jubilee a celebration of international science.