Ernst Mach (18 Februrary, 1838 – 19 February, 1916), made major contributions to, physics, philosophy, and physiological psychology. In physics, the speed of sound bears his name, as he was the first to systematically study super-sonic motion. He also made important contributions to understanding the Doppler effect. His critique of Newtonian ideas of absolute space and time were an inspiration to the young Einstein, who credited Mach as being the philosophical forerunner of relativity theory. His systematic skepticism of the old physics was similarly important to a generation of young German physicists.
In philosophy, he is best known for his influence upon the Vienna Circle (a predecessor of which was named the Ernst Mach Verein), his famous anti-metaphysical attitude (which developed into the verifiability theory of meaning), his anti-realist stance in opposition to atomism, and in general for his positivist-empiricist approach to epistemology.