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stcin’s thcory of rclativity. His lcttcrs to Mach focuscd morc and morc on this one issuc. Both sides of the corrcspondcncc havc now bccn locatcd as wcll as a number of rclevant lcttcrs from Albert Einstein and Ludwig Mach to Petzoldt.⁴⁰ Unfortunatcly, thcrc is one conscipu-ous gap, namcly, Ernst Mach's lcttcrs to Pctzoldt from 1906 to 1913. Ali are missing.

Pctzoldts lcttcrs to Mach during 1910 and 1911 rcvcal that both men still hcld major objections to the theory of rclativity. Pctzoldt was cs-pccially disturbed by the principlc of the constant vclocity of light, and Mach, by cpistcmological considcrations. “You wrotc mc last that on the epistcmological sidc thcrc seemed to be soinc dcficicncics in the principlc of rclativity; I also believc that. . . . The constant speed of light scems to play a peculiarly ‘na’ive’ role. It is constant for dif-ferent spacc-timc-systcms only by dcfinition. . . .”^r,°

On the other hand, cven at this timc Pctzoldt was attractcd to the thcory\s “rclativism” as if it wcrc related to Machs cpistcmological brand or a physical dcvclopmcnt from it. Mach, howevcr, had already begun urging Pctzoldt to rcad Hugo Dinglcr’s books, as if hc had started to noticc the epistcmologically alicn naturę of what Einstein meant by “rclativity.” Pctzoldt continucd: “But in any casc, in theo-retical physics as wcll as in mathematics, I find the modern devclop-ment wondcrful. Becausc of it, all absolutism and a priorism are fin-ished. Old Protagoras is rising from his gravc, a rebirth, now that the gushing currcnt of the holy spirit of rclativism is oncc again hcing followcd.”⁶¹

In 1912 Pctzoldt published the first of many artides relating Mach’s cpistcmology with Einstein'$ theory. He also republished a 1906 book, added fifty^ight pages to it, and inserted the word "rclativistic" into the old titlc, so that it now rcad The World Problem from the Stand-point of Relatiuistic Positirism (1912). Pctzoldt had struck a popular vcin. This retitlcd book bccamc by far his best-known publication and hclpcd place him in the van among the numerous writers attempt-ing to establish Mach as Einstcin’s forerunner.

In May and June of 1913 Pctzoldt sent three lcttcrs to Mach on the theory of relauvity, cach morc favorablc than the last.⁶² Hc was espe-cially impressed with the fact that Einstein’s new theory of generał rela* tivity rested on Mach’s suggestion conccrning Newton’s buckct cx-periment, that is, on what we now cali Mach’s principlc. Petzoldt also bclicvcd that the generał theory should hc ablc to climinatc the “abso-

lute" constancy of the vclocity of light, which had long bccn an cpis-temological annoyance to Mach and his friends. Herc is part of one of Pctzoldt’s lcttcrs to Mach, dated Junc 6, 1913: "The day bctorc yesterday, 1 spokc to Professor [Max vonJ Lauc. . . . Einstein is said to be csscntially finished with his cxplanation of gravitation and dc-clarcs that tliis is his best work so far. According to Lauc, he makes the ccntrifugal events of the relativc rotations of masses dependent on each other, that is, exactly as you havc done.”

Less than three wceks later, on Junc 25, 1913, an enthusiastie Albert Einstein wrote directly to Mach about his new theory and repeated what Pctzoldt had said about Mach’s notion that local inertia may be dependent on the totality of the stars.⁶³ Mach had criticizcd Ncwton’s bucket cxpcriment in order to place cpistcmological rclativity, the notion that "all phenomena are dependent on one another,” at the core of Newtonian physics. He had no intenuon of employing Mach’s principlc in such a way as to replace Newtonian physics or to encourage a new spcculauve system. Mach had opposcd Minkowski’s four-diinensional theory; hencc, one can easily imaginc his rcaction to Einstcins latcst copious usc of non-Euclidcan geometry. Einstcins 1913 preliminary version of his generał theory, which would not be fully worked out umil 1916, probably was the most important factor in provoking Mach into writing his 1913 preface to his book on opdcs. Einstein s ideas too closely rcsemblcd those of Zdllncr, both with re-spect to the usc of multidimensions in physics and in its appcal to a so-callcd curvcd spacc.⁶⁴

Mach’s preface was dated “July 1913," which has suggested that it was written only days after receiving Einstcins letter. On the other hand, Mach rcccivcd numerous visitors during July and August, in-cluding both Dinglcr and Pctzoldt, hence, we should be cautious in our conclusion, sińce other peopie besides Einstein may havc influcnced the writing of the preface against the theory of relativity.⁵⁵

Mach seems to havc written the preface, not becausc he thought his book on optics was ready to be published or bccause hc wanlcd to publish it at that time, but apparently, in order to have his opposiuon to Einsteins theory of relativity on record in case of his death. Ihc iitain point in his preface was to deny Ute claim of Frank, Pctzoldt, and at that time of Einstein himself that hc was a forerunner of Einstein^ theory of rclativity or (by implication) of any form of thcorctical physics at all.⁶⁰

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