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1938 After analyzing decades of temperature readings, British engineer George Callendar describes what is later known as the greenhouse effect
1939 First flight by a jet aircraft, built by Germany's Ernst Heinkel
1939 Swiss chemist Paul Muller determines that ddt is a powerful insecticide
1940
1940 French boys searching for their dog stumble onto the Lascaux cave, whose walls are covered with spectacular paintings and engravings dating from the Ice Age
1940 American surgeon Charles Drew devises a method for long-term storage of blood plasma, which can then be used for transfusions
1941 U.S. researchers Lyle Goodhue and William Sullivan adapt an earlier idea for dispersing liquids and powders in a spray. Result: the aerosol can
1942 A team headed by Italian physicist Enrico Fermi produces the first nuclear chain reaction
1942 Frenchmen Jacques-Yves Cousteau and Emile Gagnan perfect the Aqua-Lung, a self-contained underwater breathing apparatus, or scuba
1942 Germany successfully launches the V-2, a surface-to-surface missile developed with the help of rocket scientist Wernher von Braun
1943 British mathematician and cryptographer Alan Turing helps build an electronic computer, the Colossus, that will be used by the Allies to crack German codes
1943 Dutch physician Willem Kolff invents the dialysis machine, used to cleanse the blood when a patient's kidneys malfunction
1943 After accidentally swallowing synthetic lsd, Swiss chemist Albert Hofmann discovers the drug's hallucinogenic effects
1943 Publication of Being and Nothingness establishes Jean-Paul Sartre as the leading French existentialist
1944 In Mexico, American plant pathologist Norman Borlaug starts developing high-yield grains that, two decades later, will fuel the green revolution
1945 U.S. pilots cruising at high altitudes discover powerful west-to-east wind systems, later called jet streams
1945 U.S. planes drop atom bombs on Hiroshima and Nagasaki
1945 The U.S. Public Health Service begins adding fluoride to the water supply in order to reduce the incidence of tooth decay
1945 Raytheon technician Percy Spencer accidentally discovers microwave cooking when microwave signals melt a candy bar in his pocket
1946 John Mauchly and John Eckert unveil ENIAC, the first fully electronic computer
1946 American pediatrician Benjamin Spock publishes The Common Sense Book of Baby and Child Care
1947 Bedouin shepherds find Dead Sea Scrolls hidden in clay jars in Israel's Qumran Cave, overlooking the Dead Sea
1947 American Edwin Land demonstrates the Polaroid camera he invented
1947 Norwegian ethnologist Thor Heyerdahl sails from Peru to Polynesia on the wooden raft Kon-Tiki to support his theory that pre-Incan peoples reached South Pacific islands by sea and colonized them
1947 U.S. Air Force test pilot Charles (Chuck) Yeager breaks the sound barrier
1947 A research team at Bell Laboratories led by William Shockley, John Bardeen and Walter Brattain invents the transistor
1947 U.S. chemist Willard Libby develops radiocarbon dating, which can determine the age of objects made of organic materials, such as wood and bone