Mach, Ernst (1838–1916)

Austrian philosopher and physicist. He was an empiricist, believing that science is a record of facts perceived by the senses, and that acceptance of a scientific law depends solely on its standing the practical test of use; he opposed such concepts as Isaac Newton's ‘absolute motion’. Mach numbers are named after him.

Life Mach was born in Turas, Moravia (now in the Czech Republic), and studied at Vienna. He was professor at Graz 1864–67, Prague 1867–95, and Vienna 1895–1901. He was then appointed to the upper chamber of the Austrian parliament.

Physiological phenomena Mach studied physiological phenomena such as vision, hearing, our sense of time, and the kinesthetic sense. He investigated stimulation of the retinal field with spatial patterns and discovered a strange visual effect called Mach bands. This was subsequently forgotten, and was rediscovered in the 1950s.

Wave phenomena He investigated various aspects of optics, and wave phenomena of mechanical, electrical, and optical kinds. In 1887 he published a work on the photography of projectiles in flight, which showed the shock wave produced by the gas around the tip of the projectile. The Mach angle describes the angle between the direction of motion and the shock wave, and Mach found that it varies with the speed of the projectile. In 1929 the term Mach number came into use.

Theory Mach postulated that all knowledge is mediated by perception, and believed that the greatest scientific advances would only arise through a deeper understanding of this process.

Mach's book Die Mechanik 1863 gave rise to debate on Mach's principle, which states that a body could have no inertia in a universe devoid of all other mass as inertia depends on the reciprocal interaction of bodies, however distant. This principle influenced Albert Einstein.