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. Rare ALS in German, signed “E. Mach,” one page, 5.25 x 3.5, July 20, 1897. Letter to bookseller and historian Karl Junker. In part (translated): “I also wondered why the report is not printed in the almanac. Incidentally, it is hardly conceivable that all reports are printed on negotiations.” In fine condition, with two punch holes to top edge and a uniform shade of mild toning. Mach is uncommon in any form. RR Auction COA.
