Portal:History of science

Nuclear fission was discovered in December 1938 by chemists Otto Hahn and Fritz Strassmann and physicists Lise Meitner and Otto Robert Frisch. Fission is a nuclear reaction or radioactive decay process in which the nucleus of an atom splits into two or more smaller, lighter nuclei and often other particles. The fission process often produces gamma rays and releases a very large amount of energy, even by the energetic standards of radioactive decay. Scientists already knew about alpha decay and beta decay, but fission assumed great importance because the discovery that a nuclear chain reaction was possible led to the development of nuclear power and nuclear weapons. Hahn was awarded the 1944 Nobel Prize in Chemistry for the discovery of nuclear fission.

Hahn and Strassmann at the Kaiser Wilhelm Institute for Chemistry in Berlin bombarded uranium with slow neutrons and discovered that barium had been produced. Hahn suggested a bursting of the nucleus, but he was unsure of what the physical basis for the results were. They reported their findings by mail to Meitner in Sweden, who a few months earlier had fled Nazi Germany. Meitner and her nephew Frisch theorised, and then proved, that the uranium nucleus had been split and published their findings in Nature. Meitner calculated that the energy released by each disintegration was approximately 200 megaelectronvolts, and Frisch observed this. By analogy with the division of biological cells, he named the process "fission". (Full article...)

The Flammarion woodcut is an enigmatic woodcut by an unknown artist. It is referred to as the "Flammarion woodcut" because its first documented appearance is in page 163 of Camille Flammarion's L'atmosphère: météorologie populaire ("The Atmosphere: Popular Meteorology," Paris, 1888).

The woodcut depicts a man, dressed as a medieval pilgrim and carrying a pilgrim's staff, peering through the sky as if it were a curtain to look at the inner workings of the universe. One of the elements of the cosmic machinery bears a strong resemblance to traditional pictorial representations of the "wheel in the middle of a wheel" described in the visions of the prophet Ezekiel (see Merkabah). The caption in Flammarion's book translates as "A missionary of the Middle Ages tells that he had found the point where the sky and the Earth touched..." The image accompanies a text which reads, in part, "What, then, is this blue sky, which certainly does exist, and which veils from us the stars during the day?" The woodcut is often described as being medieval due to its visual style, its fanciful vision of the world, and to what appears to be a depiction of a flat Earth.

...that Einstein's famous letter to FDR about the possibility of an atomic bomb was actually written by Leó Szilárd?

...that geology was transformed in the latter part of the 20th century after widespread acceptance of plate tectonics?

...that the idea of biological evolution dates to the ancient world?

John Harrison (3 April [O.S. 24 March] 1693 – 24 March 1776) was an English carpenter and clockmaker who invented the marine chronometer, a long-sought-after device for solving the problem of how to calculate longitude while at sea.

Harrison's solution revolutionized navigation and greatly increased the safety of long-distance sea travel. The problem he solved had been considered so important following the Scilly naval disaster of 1707 that the British Parliament was offering financial rewards of up to £20,000 (equivalent to £3.97 million in 2025) under the 1714 Longitude Act, though Harrison never received the full reward due to political rivalries. He presented his first design in 1730, and worked over many years on improved designs, making several advances in time-keeping technology, finally turning to what were called sea watches. Harrison gained support from the Longitude Board in building and testing his designs. Towards the end of his life, he received recognition and a reward from Parliament. (Full article...)

June 17

• 1714 - Birth of César-François Cassini de Thury, French astronomer (d. 1784)
• 1832 - Birth of Sir William Crookes, English physicist and chemist (d. 1919)
• 1898 - Birth of Carl Hermann, German physicist (d. 1961)
• 1917 - Birth of Atle Selberg, Norwegian mathematician
• 1920 - Birth of François Jacob, French biologist and Nobel Prize laureate
• 1940 - Death of Arthur Harden, English chemist and Nobel Prize laureate (b. 1865)
• 1996 - Death of Thomas Kuhn, American philosopher of science (b. 1922)
• 2001 - Death of Donald J. Cram, American chemist and Nobel Prize laureate (b. 1919)