April 23: Administrative Professionals' Day in Canada and the United States ( 2008); World Book and Copyright Day; Children's Day in Turkey; St George's Day in various countries.

• 1661 – Charles II was crowned King of England, Ireland, and Scotland at Westminster Abbey.

• 1827 – Irish mathematician and physicist William Rowan Hamilton (pictured) presented his Theory of Systems of Rays.

• 1920 – The Grand National Assembly of Turkey, the Turkish unicameral parliament, was founded in Ankara in the midst of the Turkish War of Independence.

• 1923 – Gdynia was inaugurated as a Polish seaport on the coast of Gdańsk Bay, a southwestern bay of the Baltic Sea.

• 1961 – Dressed in his 1940s-vintage general's uniform, President Charles de Gaulle delivered a televised speech calling on the military personnel and civilians of France to oppose the Algiers putsch, a coup d'état attempt against him.

• 1968 – Students protesting the Vietnam War at Columbia University in New York City took over administration buildings and shut down the university.