Sir, – While I enjoyed Frank McNally's article (An Irishman’s Diary, October 25th) on the potential for confusion in the complexities of timekeeping in Ireland and England circa 1920, I fear he over-simplified matters by saying Dublin Mean Time or Dunsink Time was "apparent time". Apparent solar time is based on the successive passages of the sun across the meridian and these intervals are not uniform. It is the time displayed by a sundial. Most clocks advance at a constant rate and instead keep a "mean" time, where these differences are averaged over the solar year. – Yours, etc,
JIM BENNETT,
Science Museum,
Exhibition Road,
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South Kensington,
London, England.