Ernst Mach
Notes
Ernst Mach (1838–1916), Austrian physicist and philosopher, after whom the speed of sound is counted. His Analysis of Sensations (1886) held that the world consists of "elements" (colours, sounds, pressures) which are physical when considered in one set of relations and psychological in another, which makes him a founder of neutral monism. His insistence that science should speak only of what can be observed shaped the logical positivists and, for a time, made him an opponent of atoms. He appears here as the point where a respectable empiricism tipped over into a metaphysics.
Wikipedia: https://en.wikipedia.org/wiki/Ernst_Mach