Make some time for Killruddery’s water clock

‘The most accurate water clock ever’, forgotten for over 20 years, is being restored at Killruddery estate

'The most accurate water clock ever’, forgotten for over 20 years, is being restored at Killruddery estate. Video: Daniel O'Connor


It’s a wonderful Heath Robinson contraption. There’s a bicycle wheel, a toilet cistern, the casing from a shell, even some antique Meccano. Yet this odd assemblage, together with a long pendulum weighing 112lb, is arguably the most accurate water clock ever.

The ingenious and complex device was conceived and built around 1903-1906 by the 13th Earl of Meath, at his family’s Killruddery estate near Bray in Co Wicklow. When the earl tested it in 1926, the clock was accurate to 0.33 seconds per day or about 10 seconds a month – and was probably the only water clock that ever had a second hand.

British expert Charles K Aked, writing in the Horological Journal in the 1980s, reckoned it was the most accurate water clock ever. Forgotten for more than 20 years, it is now being lovingly restored and is “flowing” again, and accurate to about two minutes a month.

Water clocks were among the earliest timepieces, developed thousands of years ago as simple vessels that filled or emptied over time. Killruddery’s clock is different, however. It is probably more accurate to call it a hydraulic clock. Housed in a tower with three clock faces that gave the time to estate workers and locals, it doesn’t use water to measure time, but to power the clock, and in three different ways: first, to push the pendulum (the timekeeper, so to speak); then to power the clock train, which drives the hands; and to power the striking train, which triggers the hammer, that strikes a gong on the hour.

The water flows from nearby Little Sugar Loaf. Reduced to the thickness of a pencil, it falls inside the clock tower, and is used for precisely 0.1 of a second to push the pendulum. This keeps the clock going indefinitely, no battery or winding needed. For precisely one second, the water then falls on and depresses a plate that controls the escapement, or counting mechanism. And for 1.4 seconds the water is deflected away to collect in tanks, from where it is used to drive the clock and striking mechanisms. This cycle repeats every 2.5 seconds. The ingenious design leaves the pendulum free, or decoupled from the going train: it only has to swing, and the system takes effectively no energy from it, which is what makes the clock so accurate.

Free-pendulum clock

The designer, Reginald Le Normand Brabazon (1869-1949), didn’t invent the free pendulum – that was invented about 40 years earlier by Belfast-born physicist William Thomson, Lord Kelvin. But Brabazon’s free-pendulum clock is the only water-powered one, and was, for a few years, probably the most accurate.

It has a conventional clockwork mechanism, which was made by Dublin clockmakers Challoner, of Grafton Street. The rest is a scrap heap of parts, all precisely connected and calculated.

Brabazon incorporated a tremendous range of engineering solutions to create his device. Everything from a delicate “cat’s cradle” to control the plate that deflects the stream of water (originally made of silk thread, now restored with fishing line), to a zinc compensation tube (sadly missing) to compensate for temperature differences and to fine-tune the pendulum to fractions of a second. (To learn more, Aked’s 1980s articles are full of detail and well worth tracking down.)

Brabazon trained as a soldier, but his hobbies were gardening and clocks. At 19, he and his brother repaired the clock that originally occupied the clock tower. In his 30s, between serving in the Boer wars and the first World War, he perfected his water clock. Later he collaborated with a noted electric clock designer, George Bennett Bowell. London’s Science Museum has one of their Meath-Bowell clocks.

Killruddery clock worked continuously for more than 80 years – with daily maintenance to clear flies and leaves from the tubing – but eventually fell into disrepair. Now, industrial heritage expert Reggie Goodbody, who is skilled in boat-building, milling and musical instruments, is restoring it, under the watchful eye of Brabazon’s grandson, the 15th earl, John Ardee. Last autumn, Goodbody and his team coaxed the striking mechanism to work and he says it was “music to our ears”.

The project won the best restoration award last autumn from the Industrial Heritage Association of Ireland. On July 20th, this historic device will feature on Clockwork day at Killruddery, and Goodbody will give tours of the now-working clock ( It’s a wonderful opportunity to see some unique Irish engineering heritage.

Mary Mulvihill writes about Ireland’s scientific heritage, and tweets at @ingeniousIE

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