2026-10-04: ScienceDirect / Isidore (Vigier 1997), via Google results only

Query: Google Vigier 1997 "Physics Letters A" Sagnac effect photon mass Kelly. Result: partial (bibliographic data and snippets only; full text not opened).

Found [web]

• J.-P. Vigier, "New non-zero photon mass interpretation of the Sagnac effect as direct experimental justification of the Langevin paradox", Physics Letters A 234(2), 75-85 (15 Sept 1997). ScienceDirect abstract page (https://www.sciencedirect.com, pii not recorded); the snippet shows that its reference list includes "A.G. Kelly. Institute of Engineers of Ireland, Monograph. (1995)" and Dufour and Prunier. Google shows about 79 citations. A PDF copy appears at isidore.co (misc/Cosmology); not downloaded.
• A ResearchGate paper "Re-examine the two principles of Special Relativity and ..." cites Vigier 1997 together with Wolf and Petit 1997 (Phys. Rev. A 56, 4405), which is on GPS clock synchronisation.

Bearing on the claims

• Claims 2, 3, 5: a professional physicist used Kelly's 1995 monograph in a peer-reviewed journal. This is support or extension by another (priority 2), though Vigier's framework (non-zero photon mass, Langevin) differs from Kelly's.