2026-10-04: Wikipedia, "Sagnac effect"

Query: Google Einstein 1914 Harress experiment "Astronomische Nachrichten" Sagnac Einstein mention; then https://en.wikipedia.org/wiki/Sagnac_effect (raw wikitext fetched and grepped for "Einstein was aware", "866", "0.07"). Result: partial (one relevant passage; Sagnac's disc area not found in the article).

Found [web]

• "Einstein was aware of the phenomenon of the Sagnac effect through the earlier experiments of Franz Harress in 1911." Harress's result was reanalysed in 1914 by Paul Harzer (Astronomische Nachrichten 198, 377-392), "who claimed the results were at odds with special relativity. This was rebutted by Einstein." Harress died in WWI; Otto Knopf published his results in 1920 (Annalen der Physik 62, 389-447) at von Laue's urging.
• The Google results give Einstein's note as: A. Einstein, "Bemerkungen zu P. Harzer's Abhandlung 'Über die Mitführung des Lichtes in Glas und die Aberration'", Astronomische Nachrichten 199 (1914) (cited in G. O. Mueller's bibliography at mahag.com and a Scribd copy). Darrigol 2014, "Georges Sagnac: A life for optics" (Comptes Rendus Physique), is another source on Harzer's correction.

Bearing on the claims

• Claim 6 (Einstein never mentioned Sagnac or Michelson-Gale): Kelly's statement concerns the Sagnac (1913) and Michelson-Gale (1925) tests by name. The record found shows that Einstein wrote in 1914 on Harress's rotating-prism experiment, which is now classed as a Sagnac-type experiment. This is evidence that bears directly on the claim. Whether Einstein named Sagnac anywhere (e.g. in correspondence) is not settled by this search.