[1] Dunsink's most famous director was William Rowan Hamilton, who, amongst other things, discovered quaternions, the first non-commutative algebra form, while walking from the observatory to the city with his wife.

This Observatory, endowed by Francis Andrews, esq., LL.D., Provost of Trinity College, and erected in 1785, was placed, by statute, in 1791, under the management of the "Royal Astronomer of Ireland," an appointment first filled by Dr. Henry Ussher, and subsequently by Dr. Brinkley, Bishop of Cloyne.

Éamon de Valera, who had driven the establishment of the Dublin Institute for Advanced Studies (DIAS) in 1940, added a School of Cosmic Physics to it in 1947, partly in order to revive the observatory, for which it was given responsibility.

Éamon de Valera's signature appears in Dunsink Observatory visitor book dated 13th January 1949.

By the late 20th century, the city encroached ever more on the observatory, increasing the atmospheric turbulence thus reducing the quality of the telescope's images.