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English summary
Bronisław Średniawa

Władysław Natanson was in the years 1891-1894 privatdozent, and in the years 1894-1935 professor of theoretical physics at Jagellonian University in Cracow. His main domains of research were: the thermodynamics of irreversible processes, theory of radiation and molecular optics. His results in thermodynamics and in the statistics of indistinguishable processes went some decades ahead of the investigations of the physicists of his time. In molecular optics he obtained important results, appreciated by his contemporaries.

Before his habilitation he was busy in the kinetic theory of gases. He studied the problem of the state of the gas tending to the state of equilibrium and to Maxwell distribution of velocites of molecules.

During the last decade of the 19th century Natanson was busy in thermodynamical research. His work in this domain can be divided into three groups. The first one consisted in the collaboration with Cracow experimentalists, who worked in low temperature physics; in the second one Natanson developed research in classical thermodynamics. The third group of his investigations in thermodynamics was the most important one. In the paper On the laws of irreversible processes he formulated in 1896 the variational principle (called by him the thermokinetic principle), which described mechanical and thermal processes. The Lagrangian of this principle was composed of mechanical Lagrangian, of the increase of internal energy and of the absorbed heat. According to Natanson both reversible and irreversible changes participate in thermodynamical processes. Accordingly, the absorbed heat is the sum of the "compensated" heat (exchanged in reversible process) and of the "non-compensated" heat (exchanged in irreversible processes). The non-compensated heat exchange is connected with the existence of its cause, which was later called entropy source.

In many papers Natanson applied his principle to thermodynamic processes and then to the hydrodynamics of viscous fluids.

Natanson's thermokinetic principle was, because of its generality, not understood by his contemporaries. The development of the thermodynamics of irreversible processes was initiated in the third decade of 20th century by the "linear" theory of Onsager, formulated independently of Natanson's research. Onsager's theory, called later "Classical irreversible thermodynamics" (CIT), was less general than Natanson's principle but it was better adapted to applications to thermodynamic processes. In the sixties and seventies two new approaches to the thermodynamics of irreversible processes were formulated: "Rational thermodynamics" (RT) and "Extended irreversible thermodynamics" (EIT). This last approach was based (of course in modern mathematical and physical language) on very similar assumptions to Natanson's theory. In this sense we can say that Natanson's thought was about one hundred years ahead of the thermodynamics of his time.

In 1911 Natanson formulated, in his paper On statistical theory of radiation, the statistics of the ensemble of indistinguishable particles. He found the function of energy partition, which for photons gave Planck's law and for solid bodies - the partition function of Einstein. This paper was also not understood by contemporaries and the partition function for indistinguishable objects was independently discovered by S. N. Bose in 1924 and then developed by Einstein. In this domain Natanson was also several years ahead of the physics of his time.
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