Ernst Mach (1838-1916) was an Austrian physicist, science historian, author and philosopher who subscribed to a positivist philosophy. He is probably best known for his surname being used to describe the speed of supersonic aircraft. He named the term after himself to express the speed of a body in relation to the speed of sound at the specified altitude and temperature. Mach 2, for example, is twice the speed of sound.
Mach was a strict empiricist who made it one of his missions in life to eliminate metaphysics and religious influence from the world of science. (See this node for a much better description of this philosophy). One of his more influential maneuvers during his academic career at Vienna University was to rethink and ultimately reject Sir Isaac Newton's Laws of absolute space and time. This heavily influenced Albert Einstein and his Theory of Relativity. Mach was also a professor at Vienna from 1895 - 1901, as well as Graz (1864), and Prague (1867).
His primary interests lay in The Doppler Effect and the physiology of sensory organs. He conducted many experiments having to do with optical, mechanical properties and wave dynamics. During this period (which was his tenure at Prague) he developed several useful measuring instruments as well as experimental techniques involving stroboscopy and photography. He created the physical proof of the Doppler Law and the Mach Law by observing projectiles at high speeds.
Mach was the first person to come to the realization that things act differently when they travel faster than the speed of sound. He wrote a paper on the subject of supersonic velocity in 1887 and predicted the existence of the cone shaped shock acoustical wave.
His best known books include:
- Die Mechanik in ihrer Entwicklung {The Science of Mechanics} (1883)
- Die Analyse der Empfindungen {Contributions to the Analysis of the Sensations} (1886)
- Erkenntnis und Irrtum {perception and error} (1905)
It's safe to say that Ernst Mach had a great influence on 20th Century thought.