Quaterion Maths

A plaque on Brougham bridge in Dublin, commemorating Hamilton's invention of Quaternions

The plaque says:

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 = i j k = −1 & cut it on a stone of this bridge