Hasenöhrl, Friedrich

views updated

Hasenöhrl, Friedrich

(b. Vienna, Austria, 30 November 1874; d. near Vielgereuth, South Tirol, Austria, 7 October 1915)

physics.

Hasenöhrl was the son of Victor Hasenöhrl, a lawyer, and Gabriele Freiin, the Baroness von Pidall zu Quintenbach. In 1884 he entered the Theresianische Akademie, from which he graduated with high standing in 1892. Although it was a family tradition, he abandoned plans for a military career and continued his education at Vienna University, where he studied mathematics and physics under Franz Exner and Ludwig Boltzmann. After receiving his Ph.D. in 1897, Hasenöhrl spent a year at Leiden as assistant to Kamerlingh Onnes and was then appointed privatdozent at Vienna. He was awarded the Haitinger Prize of the Austrian Academy of Sciences, of which he was a corresponding member, in 1905 and that year he became associate professor at the Vienna Technical University. In 1907 he succeeded Boltzmann as professor of physics at Vienna University; Schrödinger was among his students. At the outbreak of World War I, Hasenöhrl left his university post to join the army. He was killed in the battle of Isonzo.

Hasenöhrl’s first systematic research, begun for his Vienna dissertation under Exner¹ and continued in Leiden, was an experimental investigation of the temperature dependence of the dielectric constants of liquids and solids. His object was to explore the range of validity of the Mossotti-Clausius equation

with ρ the density, k the dielectric constant, and C a constant characteristic of the given material. He found, as had P. Lebedev for gases, more than reasonable agreement for a variety of substances over a significant range of temperature.

When Hasenöhrl returned to Vienna he wrote the series of papers for which he is best known, on electromagnetic radiation. of these the most important is the prizewinning essay on the effects of radiant energy within a moving cavity.² Using classical theory he showed that the trapped radiation increases the kinetic energy of the motion, the effect being equivalent to an increase in the apparent mass of the cavity by the amount , a result that he soon reduced by half. In his formula hξ₀ is the total radiant energy in the cavity and c is the velocity of light. Like other similar anticipations, this result was displaced by Einstein’s more general theorem on the equivalence of mass and energy.

In the last years of his drastically foreshortened career Hasenöhrl turned increasingly to problems in statistical mechanics and considered their relation to the foundations of quantum theory. His most significant result was a by-product, a suggested quantumtheoretical treatment of spectral formulas like those of Balmer. The ostensible object of his paper on the foundations of the mechanical theory of heat was to consider revising classical statistical mechanics to yield Planck’s and Einstein’s laws for radiation and specific heats.³ In this work he notes that Planck’s simple harmonic oscillators obey the formula

with E an energy, t the period of the oscillator, and V the volume of phase space available to an oscillator with energy ≦E. The motion within real atoms, Hasenöhrl points out, cannot be governed by a linear restoring force, and the periods of such motions are therefore energy dependent, t = t(E). Nevertheless, a natural generalization of Planck’s approach suggests that these motions too can occur only at discrete energies, E₁, E₂, E₃..., determined by the equations:

With the energy levels known, the permitted frequencies of motion are determined by

Hasenöhrl also saw that application of these formulas to the pendulum of finite amplitude produces a series, although not quite Balmer’s. A short time later K. F. Herzfeld, then a student at Vienna, showed how the Balmer formula could be derived with the aid of special assumptions about the distribution of the positive space charge in the Thomson atom.⁴

NOTES

1. “Über den Temperaturcoefficienten der Dielektricitätsconstante in Flüssigkeiten und die Mossotti-Clausius’sche Formel,” in Sitzungsberichte der K. Akademie der Wissenschaften in Wien, math.-naturwiss. Klasse, 105 (1896), 460–476.

2. “Zur Theorie der Strahlung in bewegten Körpern,” in Annalen der Physik, 4th ser., 15 (1904), 344–370; corrigendum, ibid., 16 (1905), 589–592.

3. “Über die Grundlagen der mechanischen Theorie der Wärme,” in Physikalische Zeitschrift, 12 (1911), 931–935.

4. K. F. Herzfeld, “Über ein Atommodell, das die Balmer’sche Wasserstoffserie aussendet,” in Sitzungsberichte der K. Akademie der Wissenschaften in Wien, 121 (1912), 593–601