A plaque, close to Brougham Bridge, commemorating Sir Hamilton’s discovery of quaternions. Unfortunately, vandals have spoiled this plaque. It should read the following: ‘Here as he walked by on the 16th of October 1843, Sir William Rowan Hamilton, in a flash of genius discovered the fundamental formula for quaternion multiplication i2 = j2 = k2 = ijk = −1 & cut it on a stone of this bridge.’ Photo: https://en.wikipedia.org/wiki/Broom_Bridge