Mach Ernst (1838–1916), Austrian physicist and influential philosopher of science. He was born in Turas, Moravia, now part of the Czech Republic, and studied physics at the University of Vienna. Appointed professor of mathematics at Graz in 1864, he moved in 1867 to the chair of physics at Prague, where he came to be recognized as one of the leading scientists in Europe, contributing not only to a variety of fields of physics (optics, electricity, mechanics, acoustics) but also to the new field of psychophysics, particularly in the field of perception. He returned to Vienna in 1895 to a chair in philosophy, designated for a new academic discipline, the history and theory of inductive science. His writings on the philosophy of science profoundly affected the founders of the Vienna Circle, leading Mach to be regarded as a progenitor of logical positivism. His best-known work, The Science of Mechanics (1883), epitomized the main themes of his philosophy. He set out to extract the logical structure of mechanics from an examination of its history and procedures. Mechanics fulfills the human need to abridge the facts about motion in the most economical way. It rests on ‘sensations’ (akin to the ‘ideas’ or ‘sense impressions’ of classical empiricism); indeed, the world may be said to consist of sensations (a thesis that later led Lenin in a famous polemic to accuse Mach of idealism). Mechanics is inductive, not demonstrative; it has no a priori element of any sort. The divisions between the sciences must be recognized to be arbitrary, a matter of convenience only. The sciences must be regarded as descriptive, not as explanatory. Theories may appear to explain, but the underlying entities they postulate, like atoms, for example, are no more than aids to prediction. To suppose them to represent reality would be metaphysical and therefore idle. Mach’s most enduring legacy to philosophy is his enduring suspicion of anything ‘metaphysical.’ See also LOGICAL POSITIVISM , VIENNA CIR- CL. E.M.