In this paper we would like to discuss how two physicists born in Slovakia have affected the genesis and development of quantum mechanics. We will describe contribution of Philipp Lenard and Ján Fischer.

Philipp Lenard was born at 7 June 1862 in Bratislava. His ancestors came to Bratislava from Tyrol. Lenard senior had winery in his possesion. Little Philipp received education firstly at home and from nine year in church school. In year of 1872 Philipp had went to so-called real high school in Bratislava. In center of education in this school were mathematics, physics, chemistry, geography and other science subjects. Physics was teached by Virgil Klatt.

Virgil Klatt received physics education at Vienna university attending lectures of Jozef Stefan, the discoverer of Stefan-Boltzmann law, Maximilian Petzval, the author of mathematical theory of photo objective and Josef Loschmidt – he calculated the size of molecule as first. In 1875 Virgil Klatt passed examination for getting teacher license. He was examined for example by prof. Stefan and young professor Ludwig Boltzmann.

For Klatt´s teaching was characteristic effort to approach it as soon as to practice. Klatt built up very good equipped physical cabinet in Bratislava real high school. Moreover, he was skilful mechanician and had assembled himself most of the instruments which were used by him for demonstrations and experiments in physics classes. For example, he assembled a Ruhmkorf coil with range in 42 cm – the most efficient in Hungary at that time.

During his pedagogical career Virgil Klatt systematically devoted himself to scientific research. He investigated especially electrical discharges in diluted gases, cathod rays and phosphorescence. Many instruments in physical cabinet, many demonstrations presented by these instruments in classes and systematic investigations of his physics teacher Virgil Klatt – all these facts, by our opinion, attracted interest of young Philipp to physics. Later Lenard had written about Klatt as teacher: “He tried to present physics simply and correctly. It was very pleasant to watch phenomena demonstrated by simple equipment, which was frequently assembled by Klatt himself. We were able easily to understand what structure of nature is and how nature works.” It was starting point of fruitful collaboration between Klatt and Lenard. It started at late 1870´s, continued during several decades and resulted into three big fundamental papers about phosphorescence published in 1889, 1903, 1904.

In Klatt´s school physical cabinet young Philipp Lenard had acquainted himself also with cathode rays. Later he had written that discharges in diluted gases were studied so intensively at that time only in Crookes laboratory in London and in Klatt´s school cabinet in Bratislava.

Virgil Klatt helped Philipp Lenard to become physicist also in other way: he convinced Lenard senior that young Philipp is very gifted and could make a living as scientist. Only after that Lenard´s father permitted to Philipp to study physics at the university. Originally, Philipp had to become a manager of Lenard winery.

So Lenard´s way to physics had started in Bratislava´s real high school and was initiated by his physics teacher Virgil Klatt. Subsequently Philipp Lenard became very good researcher and finaly he was one of the best experimental physicists at the last decade of 19. century and the first decade of 20. century. He attached the best results especially in two branches of physics: in investigation of cathod rays, which he started in Bratislava, and in researching of photoeffect, discovered by his master Heinrich Hertz.

a) Philipp Lenard and cathod rays

Usually two Lenard´s contribution in this field are mentioned. Firstly, he developed an idea of Heinrich Hertz and introduce in experimental physics so called Lenard window – it means that he placed at the wall of cathod tube thin aluminium foil. So he was able to lead cathod rays out of tube into open space. Owing to this fact he had better conditions for investigation of cathod rays. Moreover, in such way there was opportunity to distinguish excitation of rays in cathod tube and investigation of its characteristics.

Secondly, Philipp Lenard had found out that cathod rays going out of tube have identical properties as cathod rays inside tube, namely: it causes fluorescence, it could by deviated by magnetic field etc. Besides that

• he had proved that cathod rays cause black tracks at photographic plate, ozonization of air and ionization of gases owing what gases could convey electric current,
• he had found that cathod rays passe through open space, namely they spread through air for 10 cm, in vacuum they can go several metres without weaking, they are scattered by gases and scattering angle depends on dense of gase,
• he had confirmed that cathod rays are carrying negative electric charges and can be deviated by electric and magnetic field,
• he had demonstarted that there are two sorts of cathod rays – different sort is caused by different level of dilutation of gase and magnetic field effects in different way on different type of cathod rays.

We would like to stress that Philipp Lenard had presented own specific opinion on nature of cathod rays. Originaly there were two opposite mention: especially german physicists were convinced that we have to do with radiation. English researchers representated by William Crookes had advocated opinion that we are dealing with beam of corpuscula coming from cathod and carrying negative electric charge. Basing on results of his experiments Lenard came to the conclusion that both hypothesis have to be modified, because

• mass and size of particles of cathod rays has to be essentialy less then mass and size of molecules and even than atoms,
• on the other side, speed of particles is essentialy lower than speed of light, moreover, different sort of cathod rays are spreading by different speed.

Thus Philipp Lenard had adhered to opinion that cathod rays are neither electromagnetic radiation nor particles in classical sens but it is something intermediate – so called quanta of electricity. He was convinced that they are not substantial though they have inertia. Notwithstanding, cathod rays are carrying electric charge identical with charge of Thomson´s subatomic particle. Lenard had written:

For his investigation on cathod rays Ph. Lenard was awarded in 1905 by Nobel prize for physics.

Starting from results of his experiments on cathod rays Lenard had proposed very interesting model of atom. As fast cathod rays are able to penatrate many thousends of atoms the biggest part of atom has to be, by Lenard, empty. Besides that in atom there are so-called dynamids – pairs of positive and negative electrons with certain dipole moment. Electric field is excitated by these dynamids and such field is able to intercept slow electrons but it does not intercept fast electrons. Philipp Lenard also had calculated that in little volume dynamids are non-penetrated by any cathod rays. Volume of non-penetrated part of atom caused by dynamids is about 1/10⁹ of hole atom. As absorption of cathod rays by matter is proportional to its mass quantity of dynamids in atom is proportional its atomic mass.

So it is clear that Lenard´s model of atom contains many elements which was later used by Rutherford in his model, namely:

• volume of atom is mostly empty,
• size of non-penetrated dynamids is very close to size of Rutherford´s non-penetrated nucleus of atom.

By recollections of Rutherford´s co-worker, trying to explain results of Geiger and Marsden experiments on scattering of alpha particles on gold foils Rutherford had remembered Lenard´s experiments on penetration of cathod rays through thin aluminium foil. So one can say that Lenard´s model was, in certain sense, the starting point for building of Rutherford´s model of atom. Trying to explain Rutherford´s planetary model Niels Bohr had developed the first quantum theory of hydrogen atom.

Notwithstanding, there is also essential difference: in Lenard´s atom with atomic mass N there are k.N dynamids whereas in Rutehrford´s model there is sole nucleus which charge is not equal to atomic mass but to atomic number.

b) Ph. Lenard and photoeffect

Results of Lenard´s experiments on photoeffect were sumed in three article published in Annalen der Physik in years of 1900, 1902, 1903. Philipp Lenard had proved once more that particles leaving cathod as consequence of incidence of ultraviolet light are identical to cathod rays. Moreover, he found out that speed of such “rays” is equal 1/30 of speed of light in vacuum. So it is impossible to consider them as electromagnetic waves. Besides that he had discovered

• firstly, that speed and energy of these “quanta of electricity” does not depend on intensity of pitching light – it depends on frequency or wavelength of light,
• secondly, number of “quanta of electricity” leaving cathod in one second depends on intensity of light.

Apropos, namely in the last of mentioned papers Lenard had described absorption of cathod rays in various gases and had formulated his dynamid model of atom.

Trying to explain Lenard´s laws of photoeffect Albert Einstein had postulated quantum character of light in 1905. After Planck´s hypothesis it was second step to quantum mechanics.

Ján Fischer was born at 5 May 1905 in little town Turčiansky Svätý Martin in Central Slovakia. He had studied physics at Charles university in Prague and from 1928 to 1931 had spent three years at University of Zürich beeing postgraduate student of Gregor Wentzel.

At 1926-1928 Wentzel had published five papers on theory of elastic and non-elastic collisions applying some ideas of Schrödinger´s wave mechanics and Born´s quantum mechanics of collisions. He had stressed that only new quantum mechanics offered a possibility to solve problem of photoeffect, collision of electrons and scattering of Röntgen radiation on particles.

Namely on these problems was concentrated attention of young Slovak theoretician Ján Fischer in two papers completed in Zürich and published in Annalen der Physik in 1931. The first was entitled “Contributions to Theory of X-Rays Absorption” and second one – “On Retarded Matrix Elements in the theory of X-rays scattering and absorption”. In the first paper Ján Fischer had discussed two problems:

• distribution of photoelectrons by direction; it was determined by angle part of wave function,
• probability of excitation depending on coefficient of absorption.

So he found full mathematical description of X-rays absorption.

In second article Fischer developed his own method for calculation of matrix integral and calculated matrix integrals for Compton effect on hydrogen atom in any initial state. After that he derived general formula for wave function describing photoefect. So he completely had solved Compton effect and photoeffect as first.

Apropos, papers of Ján Fischer were awarded by prize of Zürich university. Significance of Fischer´s results is stressed by fact that both articles were quoted by Arnold Sommerfeld in the fifth edition (1939) and in all following editions of his book Atombau und Spektrallinien and also by Hans Bethe in his Handbuch der Physik published in 1933.

In conclusion I would like to pay your attention to interesting facts concerning personal destiny of both mentioned physicists who were born in Slovakia.

After War the first Philipp Lenard jointed anti-Semitic movement in Germany and subsequently he became a follower of national socialism. Later he was a member of NSDAP and won Adolf Hitler´s confidence.

On the other side Ján Fischer had experienced consequences of national socialism philosophy and of politics of the Third Reich. In 1940 anti-Jewish laws came into force in Slovakia too. Doctor philosophy of university in Zürich, author of fundamental works on quantum theory of radiation, quoted in monography which was in 1939 published in the Third Reich, Ján Fischer beeing Jew might teach only in elementary jewish school in little Slovak town.

Two excelent physicists and two opposite destiny.