The Dublin Time Ball

Knowing the time is important for marine navigation. It allows navigators to calculate longitude, even when a ship is far from any landmark.


From the eighteenth century on, ship captains were able to rely on precise timepieces, known as chronometers, to tell the time accurately, no matter where they were in the world. Still, it was good practice to double check these nautical instruments while a vessel was in port, and so time balls became a common feature of port skylines.

In 1865, the Dublin Ballast Board decided to erect a time ball on the roof of their office, located just south of O’Connell Bridge, on the corner of Aston Quay and Westmoreland Street. As the corporation for preserving and improving the Port of Dublin, the Board no doubt saw the erection of the ball as part of their remit to represent Dublin as a modern world port.

The ball itself was a copper sphere, about four feet in diameter, with a wooden pole at its axis. At 1pm every day, the time ball would slide from the top of the pole to the bottom – a signal for navigators who wished to check their chronometers. Unfortunately, the time ball was likely more confusing than it was helpful. Positioned upriver in the city centre, the ball could not be seen by deep-sea vessels berthed downriver. Meanwhile, it was of little use to Dubliners.

The time ball fell every day at 1pm Greenwich Mean Time (GMT). However, GMT did not apply in Ireland until the Time (Ireland) Act was passed in 1916. Since 1880, Dublin Mean Time had been the legal time for all of Ireland: 25 minutes and 21 seconds later than GMT. This meant that when the ball fell at 1pm GMT, the local time was 12:35pm.

Dublin Mean Time was set by the Dunsink Observatory, then located outside of the city to the north of Phoenix Park. Dunsink opened in 1785 as the observatory attached to Trinity College Dublin, and is the oldest purpose-built scientific research centre in Ireland. After telegraph lines became available, four public clocks in Dublin were automatically synchronized with those in Dunsink to keep them on time. These clocks adorned the façades of the General Post Office, Trinity College, the Bank of Ireland at College Green, and the Ballast Office. However, this meant that the Ballast Office’s notoriously accurate clock and the time ball told different times.

The confusion caused by the time ball is recorded in James Joyce’s Ulysses (1922). Crossing O’Connell Bridge, and unable to see the clock on the Westmoreland Street façade, Leopold Bloom notes: 'Timeball on the ballast office is down. Dunsink time.' But by the time Bloom reaches Nassau Street, he has to pause and correct himself: 'Now that I come to think of it that ball falls at Greenwich time.' Although the time ball was a symbol of Dublin’s status as a modern world port in the nineteenth century, therefore, for Joyce it also signals how modern Ireland beats a different rhythm to Britain, and, indeed, the rest of Europe.

Recognising that the time ball was of little use to ships, it was eventually removed from the roof of the Ballast Office to the Berthing Master’s Office at the east end of Sir John Rogerson’s Quay. However, even here it was still out of sight of larger deep-sea vessels in Alexandra Basin. By the mid-twentieth century, the ball no longer served any purpose, and was given to Dunsink Observatory. Nevertheless, this distinctive piece of Dublin’s marine architecture is still remembered today. It is commemorated by the installation of a four-tonne stainless steel ball now in place at Dublin’s Port Centre, inspired by the copper original.


Ballast House, Aston Quay, Temple Bar, Dublin 2 ~ It is possible to visit all of the locations mentioned in this piece. Ballast House, on the corner of Aston Quay and Westmoreland Street in Dublin, is now occupied by shops, but much of its Georgian façade has been preserved. The Ballast Office and its look-alike, the Carlisle Building, were both featured in the series of views of Dublin by Samuel Brocas dated 1817. Dunsink Observatory is located about 8 kms northwest of Dublin city centre, in the suburb of Castleknock. Although not always open to the public, Dunsink Observatory runs visitor nights twice a month during the winter months, as well as other events. The recently constructed stainless steel ball, inspired by the original time ball, is located in the Dublin Port Centre, accessible through pedestrian entry points at Alexandra Road and East Wall Road.