The 'half of Euler's output came after blindness' figure traces to Ferdinand Rudio's 1883 centenary lecture, not an independent modern tally

The oft-repeated statistic that roughly half of Leonhard Euler's total output was produced after he went completely blind has a locatable textual origin. Ferdinand Rudio, professor at the Federal Polytechnic in Zurich, delivered a centenary tribute to Euler at the Zurich Town Hall on 6 December 1883, stating that "almost half of his entire production dates to the years when Euler was bereft of a scholar's most valuable organ." This is the earliest occurrence of the "half" fraction located in this search, predating Allyn Jackson's 2002 Notices of the AMS wording — "Amazingly, half of his output came after his blindness" (claim-euler-produced-large-share-of-output-after-going-blind) — by 119 years. MacTutor's own biography page repeats the same fraction independently in narrative voice, but without an inline citation.

None of the three appearances shows its method or cites a bibliographic count; Rudio delivered the figure as rhetorical color in a public address. This does not make "half" wrong, but it means the figure's apparent multi-source support may be one 1883 sentence echoing forward through retellings rather than several independent tallies converging on the same number — a distinction the existing conflict between the "half" and "≈a third" figures did not previously have visibility into.