IMG71

Ernst Mach

was ncvcr clcarly cxprcsscd, and, whilc an cxtcnsion of common scnsc practical, and inforraative, was a rathcr complcx, mattcr. Mach’s thcory' on thc othcr hand, whilc in many ways impractical and uninformativc! was thc csscncc of simplicity. Causcs did not cxist, cxccpt insofar as one chosc to cali constant relations and mathcmatical functions “causcs.” Mach’s interest in relational constancies, howcvcr, led him into a fur-ther dcvclopmcnt of his appeal to thc stars. “I [Mach] have remained to thc present day [1912] thc only one who insisis upon referring thc law of inertia to thc carth and in thc casc of motions of great spatial and tcmporal cxtcnt, to thc fixcd stars." ^,n But Mach was not quitc alonc. At almost c.wactly thc time hc wrotc this, Albert Einstein introduccd a variation of Mach’s star spcculation, which hc callcd “Mach’s principle,” into his dcvcloping generał thcory of rclativity. I ani, howcvcr, getting ahead of thc story. Sufficc it to say herc that the plausibility of trying to cxplain thc law of inertia by relating it to thc carth and stars rests nowadays on thc conceiv-ability that thc totality of all stars and mattcr in thc universe may excrt somc kind of supcrgravitational influence on locnl motion. The cxtcnt, however, to which Einstein and latcr physicists havc under-stood what might best be callcd “The Bcrkclcy-Mach principle" within thc contcxt of Machs phenomenalism is perhaps nogreater than Machs similar attempts to understand Newton’s idcas within thc framework of Newton’s philosophy. We might mention in passing that Boltz-fn31.11, who rcad Mach’s books closcly. could not resist calling Mach’s star speeulations “transccndcnt” (i.e., “metaphysicar). He thereBy .succcssfully played turnabout with one of Mach’s favorite abusive tools.⁷¹ Not only did Mach havc no idea how the stars could afTcct local rnotion, but in referring to thc stars as a vague whole, hc was referring to many unobservcd entities, perhaps many unobscrvablc entitics, and quitc likcly numerous heavenly bodies with characteristics incompatiblc with his cxplanation of inertia. On thc other hand, Mach rarcly grievcd ovcr thc fatc of “mcrc theorics,” even his own. New “simpler” theories with morę value for science or for satisfying human “biological needs” might always appear. In any case, all theories would eventually be rcplaccd by “mathcmatical functions” referring dircctly to expericnceablc sensations.

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Mach Shoct^ Waves i

One day in 1881 while Ernst Mach was visiting thc First International Electrical Exhibition in Paris, where hc was also a delegate to thc First Electro-Technical Congress, hc happened to hcar a leeture by the Bclgian artillerist, Louis Melsens.¹ Mach was so struck by one of Mel-scns’s theories about the explosivc impact of cornprcsscd air as a cause for the ćrater-like wounds in victims shot by gunfirc during the Franco-Prussian War that, on returning to Prague, hc dccided that when hc could find thc opportunity, he would set up an expcrimcnt to test thc thcory.*

Dr. Mer/.kirch of thc Ernst-Mach-Institut in Freiburg in Germany givcs two rcasons for Mach’s interest:

One rcason was thc wcll-know obscrvation of artillcrymcn that one per-ceivcs usually two bangs whilc a fast projcctilc is flying by. One of them had to hc thc hang originating at thc ntuzzle of thc gun. The sccond, how-evcr, found no appropriatc e.\planation; it did not appear when thc speed of thc projcctilc was rather Iow. The sccond rcason traccs back to the German-Frcnch war of 1870/71. It had then becn noticed that the Frcnch Chassepót-bullcts caused big, crater-shapcd injurics; thc French had bccn charged thcrcforc with using cxplostve projcctilcs vio!ating the Interna tional Treaty of St. Petersburg of 1868, which prohibiled thc use of such projcctilcs. Thesc chargcs had bccn . . . [disputed] by thc Bclgian physi cist M. Melsens, who reported on his invcstigations in 1872 at the Royal Acadcmy of Sciences in Brussels. Hc madc thc following suppositions: (1.) A spherical projcctilc is ablc to carry a considcrablc amount of com-pressed air which depends on its vclocity; (2.) The cornprcsscd air pre-ccdcs the projcctilc and nny cause mechanical, cxplosion like effeets. The reported injurics have to be explaincd in this way.³

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