Excerpt from Wizard: Nikola Tesla - The Life and Times of a Genius: Mach's experiments in Wave Mechanics
In his laboratory, Mach had constructed a "famous instrument known as a wave machine. This device could make progressive [and standing] longitudinal [and] transverse waves..." Mach could display a number of mechanical effects with these acoustic waves and "demonstrate the analogy between acoustic and electromagnetic events." By this means, the "mechanical theory of the ether" could also be demonstrated.
By studying acoustical-wave motion in association with mechanical, electrical, and optical phenomena, Mach discovered that when the speed of sound was achieved, the nature of an air flow over an object changed dramatically. This threshold value became known as Mach I.
Mach also wrote on the structure of the ether and hypothesized that it was inherently linked to a gravitational attraction between all masses in the universe. Influenced overtly by Buddhist writings, which no doubt filtered down to esoteric discussions by the university students, Mach could hypothesize that no event in the universe was separate from any other. "The inertia of a system is reduced to a functional relationship between the system and the rest of the universe." This viewpoint was extended to the relationship of mental events to exterior influences. Like Stumpf, he agreed that every mental event had to have a corresponding physical action.
Since Mach's writings so closely parallel Tesla's later research and philosophical outlook, Mach seems a curious omission from Tesla's published writings.
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