16th of October 1843 Sir William Rowan Hamilton in a flash of genius discovered the fundamental formula for quaternion multiplication i 2 = j 2 = k 2 = ijk = −1 and cut it on a stone of this bridge

 the 16th of October 1843 Sir William Rowan Hamilton in a flash of genius discovered the fundamental formula for quaternion multiplication i 2 = j 2 = k 2 = ijk = −1 and cut it on a stone of this bridge

https://people.math.harvard.edu/~knill/teaching/math22b2022/handouts/lecture04.pdf

https://www.math.mcgill.ca/labute/courses/133f03/VectorHistory.html