Geiger–Marsden experiment (1909). Otto Hahn discovers nuclear isomerism (1921). Albert Szent-Györgyi and Hans Adolf Krebs discover the citric acid cycle of oxidative metabolism (1935-1937). Otto Hahn and Fritz Strassmann discover the nuclear fission of uranium (1938). Glenn Theodore Seaborg and colleagues create and isolate five transuranium elements. They reorganize the periodic table to its current form. (1941–1950). Miller–Urey experiment demonstrates that organic compounds can arise spontaneously from inorganic ones (1953). Melvin Calvin and Andrew Benson delineate the path of carbon in photosynthesis using Chlorella and carbon dioxide labeled with carbon-14 (14CO2) (1945–1954). Erwin Chargaff disproves the "tetranucleoide theory" of DNA structure and determines that the composition of double-stranded DNA follows the rule, %A = %T and %G = %C (Chargaff's rule). This discovery was critical to the formulation of the Watson-Crick Model of DNA structure. Neil Bartlett mixes xenon and platinum hexafluoride leading to the first synthesis of a noble gas compound, xenon hexafluoroplatinate (1962). Robert Burns Woodward announces the total synthesis of Vitamin B-12 by a team he led (1973). Insights from this work lead him and Roald Hoffmann to formulate the Woodward–Hoffmann rules for elucidating the stereochemistry of the products of organic reactions. Frederick Sanger demonstrates the dideoxy- or chain termination method for determining DNA sequences (1975). Kary Mullis demonstrates the polymerase chain reaction, a method for amplifying specific bits of DNA (1983). Economics and political science The experiments of Muhammad Yunus on the applications of microcredit and microfinance in rural Bangladesh (1971) Robert Axelrod's prisoner's dilemma computer tournaments, later documented in The Evolution of Cooperation (1984) Geology Charles Mason conducts an experiment near the Scottish mountain of Schiehallion that attempts to measure the mean density of the Earth for the first time. Known as the Schiehallion experiment (1774) Physics Galileo Galilei uses rolling balls to disprove the Aristotelian theory of motion (1602–07) Otto von Guericke demonstrates atmospheric pressure using Magdeburg hemispheres (1654) Robert Boyle shows that the volume of a given amount of gas is inversely related to the pressure upon it (1660) Benjamin Franklin beginning in 1747 describes experiments in letters to Peter Collinson demonstrating electrical principles which were published in a book called Experiments and Observations on Electricity. Alessandro Volta constructs a new source of electricity, the electrical battery (1796) Henry Cavendish's torsion bar experiment measures the force of gravity in a laboratory (1798) Thomas Young shows that light is a wave in his double-slit