[en] Observations of Aql X-1 (3U 1908 + 00) with the Ariel V Sky Survey instrument during the decay of the 1975 June X-ray flare (first reported by Buff), indicate a modulation with a period of 1.30 +- 0.04 days, JD of phase zero 2442593.63 +- 0.15. (author)