On April 23 in 1827, Sir William Rowan Hamilton presented a theory of a single function (Theory of Systems of Rays), now known as Hamilton's principal function, at the Royal Irish Academy in Dublin.
Although he was still an undergraduate, only 21 years old, his work is one of the important works in optics. It provided a single function that brings together mechanics, optics and mathematics. It led to establishing the wave theory of light, which gives that light is a form of energy that travels in waves.