Broom Bridge, Railway bridge in Cabra, Ireland
Broom Bridge is a stone railway bridge that crosses the Royal Canal and connects Broombridge Road on both sides in north Dublin. The structure allows trains on the Dublin to Maynooth line to pass over the waterway while serving as a pedestrian crossing above the water.
The bridge gained fame through a mathematical event on October 16, 1843, when Sir William Rowan Hamilton carved the quaternion multiplication formula i² = j² = k² = ijk = -1 into its surface. This moment of inspiration marks a significant breakthrough in mathematical history that happened by chance at this exact location.
The bridge takes its name from William Broome, a director of the Royal Canal company who lived in the surrounding area during the 1800s. This connection to local figures reflects how neighborhoods preserve the memory of those who shaped their infrastructure.
Pedestrian access is available from both sides of Broombridge Road, and the structure offers clear views across the canal. It is best visited during daylight hours to fully appreciate the stonework and the surroundings of the Royal Canal.
Every October, mathematicians from many countries gather at this bridge to honor Hamilton's mathematical breakthrough. They undertake a shared walk from Dunsink Observatory to the place where the scholar left behind his groundbreaking formula.
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