Austrian physicist and philosopher (1838–1916) who, as a result of his research into the effects of supersonic velocity, lent his name to the ratio of the speed of a projectile to the speed of sound, aka the Mach number. Though Einstein would later credit him as the forerunner of the Theory of Relativity, Mach ultimately rejected Einstein’s theory. Scarce ALS in German, signed “Mach,” on a 4.75 x 3.25 government postcard postmarked 1875. Mach writes from Prague to an unknown correspondent in Vienna (name partly removed) with a list of “fiction publishers” including Julius Günther, Robert Schaefer, and S. Mode. In fine condition, with postmark traces and mild soiling. Uncommon in any form! RRAuction COA.
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