Mach number which was also unit-first, and may have influenced the use of the term Mach. In the decade preceding faster-than-sound human flight, aeronautical engineers referred to the speed of sound as "Mach's number", never "Mach 1". Mach number is useful because the fluid behaves in a similar manner at a given Mach number, regardless of other variables. As modeled in the International Standard Atmosphere, dry air at mean sea level, standard temperature of , the speed of sound is . The speed of sound is not a constant; in a gas, it increases as the absolute temperature increases, and since atmospheric
Ernst Mach is a critical parameter in the description of high-speed fluid movement in aerodynamics and hydrodynamics. Mach also contributed to cosmology the hypothesis known as Mach's principle. From 1895 to 1901, Mach held a newly created chair for "the history and philosophy of the inductive sciences" at the University of Vienna. In his historico-philosophical studies, Mach developed a phenomenalistic philosophy of science which became influential in the 19th and 20th centuries. He originally saw scientific laws as summaries of experimental events, constructed for the purpose of making complex data comprehensible, but later emphasized mathematical functions as a more useful way to