September 18

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  1783: Mathematician and physicist Leonhard Euler dies. He made important and influential discoveries in many branches of mathematics, and introduced much of the modern mathematical terminology and notation, such as the notion of a mathematical function.

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  1947: The majority of the provisions of the National Security Act, which establishes The National Security Council and the Central Intelligence Agency, come into effect, the day after the Senate confirmed James Forrestal as the first Secretary of Defense.

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  1967: Physicist, academic, and Nobel Prize laureate John Cockcroft dies. He was instrumental in the development of nuclear power.

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  1976: Public servant and alleged time-traveller The Custodian tells a funny story about why you can't go in there.

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  1977: Voyager 1 takes first photograph of the Earth and the Moon together.