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Ernst Mach in Prague

Ernst Mach (1838-1916) spent 28 years in Prague between 1867 and 1895. He contributed to the development of several parts of physics including optics, acoustics and mechanics.

Ernst Mach was born on 18 February 1838 in Chrlice (nowadys a part of the Moravian metropolis Brno) to a German-speaking family whose name, however, betrays Czech ancestry. After completing his studies at Kromeriz Gymnasium, he enrolled for study at the University of Vienna where he studied mathematics, physics and philosophy. His early physical works were devoted to electric discharge and induction. Between 1860 and 1862 he studied in depth the Doppler Effect by optical and acoustic experiments. Already this work proved Mach's competence as a brilliant experimenter and a designer of measuring devices striving for maximum precision. In 1864 Mach became Professor of Mathematics in Graz, in 1866 he was named Professor of Physics. During this period Mach was interested also in physiology of sensory perception.

In 1867 Mach became Professor of Experimental Physics at the Prague Charles University (called the Karl - Ferdinand at that time). His lectures, accompanied by well-premeditated experiments, soon gained a reputation for their excellence and pedagogical acumen. In 1879/80 and 1883/84 Mach was elected Rector of the University. However, during his second Rectorship he resigned since he disapproved of the administrative procedure which was applied during the statutory division of Prague University into Czech and German parts beginning from the winter term 1882/83. Mach subsequently worked and lectured in the German part of the University (he was the head of the Institute of Physics) but his courses were attended by many Czech students.

Mach's scientific interests during his Prague period covered a wide cross-section of physics. The list of his works written in Prague features about 90 publications including 6 books. Naturally, he continued his previous investigations. In Prague he published papers on the physiology of sensory organs. Some of the experiments Mach conducted on himself. Most of his studies in the field of experimental physics were devoted to acoustics and physical optics. They dealt with interference, diffraction, polarization and refraction of light in different media under external influences. At the same time, Mach resumed his study of the Doppler effect. He developed a number of excellent measuring instruments which were used in research and for instruction in universities. He also invented new experimental methods in stroboscopy and photography.

These studies were soon followed by his important explorations in the field of supersonic velocity. Mach's paper on this subject was published in 1877 and correctly describes the sound effects observed during the supersonic motion of a projectile. Mach deduced and experimentally confirmed the existence of a shock acoustic wave which has the form of a cone with the projectile at the apex. The ratio of the speed v/c is now called the Mach number. It plays a crucial role in aerodynamics and hydrodynamics.

Also, while in Prague, Mach wrote his renowned and influential book on mechanics entitled Die Mechanik in ihrer Entwicklung (The Development of Mechanics), published in Leipzig, 1883. As is well-known, the purpose of Mach's Mechanik is a criticism of Newtonian physics. Although Mach was not the first to raise objections to Newton's concepts of absolute space and time and further axioms and laws (such as "action in distance"), his Mechanik obtained a spectacular response since it was written in a lucid style with clear arguments. Also, it came at the time when Maxwell's work on electromagnetic field challenged the mechanistic conception of the world: Michelson's famous experiments were first conducted in 1882. In his book, Mach provides evidence that all measurements of spatial distances, time intervals, motion velocities and the mass of physical objects are basically measurements of relative quantities, thus foreshadowing the theory of relativity. Although Mach's criticism cannot be regarded as the sole source of inspiration for the Special Theory of Relativity, Einstein himself recognized that the book "exercised a profound influence upon me...". Mach's other idea that mass is not an absolute measure of matter but is conditioned by the surrounding environment, reappeared in 1918 in Einstein's study of General Relativity in which a mathematical principle called the Mach Principle was formulated.

After 28 years of productive scientific life, Ernst Mach left Prague for Vienna in 1895.

J.Podolsky, 20 Sept 1998, <podolsky (at) mbox.troja.mff.cuni.cz>