It was with some surprise that I read Commander Sharpey-Schafer's ‘Some Notes on Astronomical Observations at Sea’ (this Journal, Vol. VI, p. 362), especially his conclusions regarding the fixing accuracy obtainable with marine sextant observations.I can makeno claim to be an experienced navigator myself, but, as a member of the staff of H.M. Nautical Almanac Office, I was privileged, in 1949, to spend three months as an observer on board H.M.S. Dalrymple, a newly-commissioned surveying ship, under the command of Captain (now Vice-Admiral Sir) A. Day.