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1914 The Panama Canal, which links the Atlantic and Pacific oceans, opens to commercial traffic
1914 Authorities institutionalize Mary Mallon, a cook popularly known as "Typhoid Mary," whose handling of food had led to at least 51 cases of the disease and three deaths since 1904
1916 Albert Einstein publishes his general theory of relativity
1917 U.S. astronomer George Hale builds a 100-in. reflecting telescope--the world's largest--on California's Mount Wilson
1918 American astronomer Harlow Shapley describes the size and structure of the Milky Way galaxy
1918 A worldwide influenza epidemic kills more than 25 million people, including some 500,000 Americans
1919 British physicist Ernest Rutherford artificially splits an atom
1920
1921 Swiss psychiatrist Hermann Rorschach introduces the inkblot test
1921 Canadian physician Frederick Banting and colleagues find a treatment for diabetes: insulin isolated from the pancreas of fetal calves
1922 British archaeologist Howard Carter opens the tomb of Tutankhamun, a little-known pharaoh who died in 1325 B.C.
1924 French physicist Louis de Broglie describes his theory that all matter behaves as both a particle and a wave, just as light does; this notion will lead to the electron microscope
1925 The teaching of evolution comes under fire at the Scopes "monkey trial" in Tennessee
1926 American physicist Robert Goddard conducts the first successful launch of a liquid-fueled rocket
1927 Werner Heisenberg devises his "uncertainty principle"
1927 Belgian astronomer and priest Georges Lemaitre proposes that the universe began with a big bang, the explosion of a highly condensed mass, which he refers to as a "cosmic egg"
1928 Scottish bacteriologist Alexander Fleming discovers penicillin
1928 American anthropologist Margaret Mead publishes Coming of Age in Samoa
1928 Greek-American physician George Papanicolaou develops the Pap smear, a screening test for cervical and uterine cancer
1928 Hungarian-born biochemist Albert Szent-Gyorgyi isolates vitamin C
1929 U.S. astronomer Edwin Hubble provides evidence that the universe is expanding
1929 American physicist Ernest Lawrence dreams up the cyclotron, the first atom smasher
1930
1930 U.S. astronomer Clyde Tombaugh discovers Pluto, the ninth planet
1930 Austrian physicist Wolfgang Pauli proposes the existence of neutrinos
1933-35 Teams in Germany and Britain independently invent radar
1934 French physicists Irene and Frederic Joliot-Curie artificially induce radioactivity
1935 U.S. seismologist Charles Richter develops a scale for measuring the strength of earthquakes
1935 Austrian zoologist Konrad Lorenz describes the process of imprinting, during which young birds attach themselves to a being or an object
1935 First use of lobotomy to treat mental illness
1936 John Maynard Keynes publishes The General Theory of Employment, Interest and Money
1938 In Italy, electroconvulsive therapy--controlled electric shocks that cause temporary loss of consciousness and seizure--is first used on mental patients