Would I be able to work out the time after an Xmas drink or two with this clock? My brow might furrow. At the time of its installation in 1852 it was a cutting edge Galvano-Magnetic Clock (electricity at the time was called Galvanism). As can be seen by its accumulating number of Xs it is a 24 hour clock. The minute and second hands are conventional but the hour arm goes round the dial only once in 24 hours, or should I say in XXIV hours.

This man stood a long time at the clock which welcomes one into the home of Greenwich Mean Time (GMT) and is called simply the Shepherd 24 Hour Gate Clock. Of course there are also the explanations of The Time Ball (which drops down at 13:00), the Ordnance Survey Bench Mark and the Public Standards of Length. Ah yes the good old days of feet and inches. The inscription of 'Shepherd Patentee' on the clock is significant because there was a dispute when he installed the clocks at Greenwich whether or not he was the inventor (he was). The galvanism or electric signalling transmitted time pulses from Greenwich to slave clocks throughout the country and rather than each area of the country having a different time (nightmare for running a railway system) there was one single time. Eventually, as Shepherd envisioned, the pulses were also sent via submarine cables across the world. The Gate Clock is the visualisation of unified time although there is a rather more workmanlike, but just as interesting, master clock in the observatory.
The Royal Observatory says the Shepherd clock is one of the most photographed objects at the Observatory (
here is an early c1870 view). I proved the Observatory right by taking a picture of the clock location as I entered the gate and a close up of the clock as I left. There was lots to see in-between those two times, not to mention tea and cake on the Gagarin Terrace.
An entry to ABC Wednesday, a journey through the alphabet, this week sojourning at X
here