The following is a list of historically important scientific experiments and observations.

See also: timeline of scientific experiments, list of famous discoveries, thought experiment.

Astronomy

• Eratosthenes measures the earth's circumference (240 BC)
• Galileo Galilei uses a telescope to observe that the moons of Jupiter appear to circle Jupiter. This evidence supports the heliocentric model, and weakens the geocentric model of the cosmos (1609)
• Ole Rømer makes the first quantitative estimate of the speed of light in 1676 by timing the motions of Jupiter's satellite Io with a telescope
• Arno Penzias and Robert Wilson detect the cosmic microwave background radiation, giving support to the theory of the Big Bang (1964)
• Researchers at the Lawrence Berkeley National Laboratory in California discover, by observing Type 1a supernovae, that the expansion of the Universe is accelerating (1998)

Biology

• Robert Hooke, using a microscope, observes cells (1665)
• Anton van Leeuwenhoek discovers microorganisms (1674-1676)
• James Lind, publishes 'A Treatise of the Scurvy' which describes a controlled ship board experiment using two identical populations but with only one variable, the consumption of citrus fruit. (1753)
• Edward Jenner tests his hypothesis for the protective action of mild cowpox infection for smallpox, the first vaccine (1796)
• Gregor Mendel's experiments with the garden pea lead him to surmise many of the fundamental laws of genetics (dominant vs recessive genes, the 1-2-1 ratio, see Mendelian inheritance) (1856-1863)
• Louis Pasteur uses S-shaped flasks to prevent spores from contaminating broth. Disproves the theory of Spontaneous generation (also known as abiogenesis). (1861) An extension of the rancid meat experiment of Francesco Redi to the micro scale.
• Charles Darwin and his son Frances, using dark-grown oat seedlings, discover the stimulus for phototropism is detected at the tip of the shoot (the coleoptile tip), but the bending takes place in the region below the tip (1880).
• Frederick Griffith demonstrates (Griffith's experiment) that living cells can be transformed via a transforming principle, later discovered to be DNA (1928)
• Alexander Fleming demonstrates that the zone of inhibition around a growth of Penicillium mold on a culture dish of bacteria is caused by a diffusable substance secreted by the mold. (1928)
• Karl von Frisch decodes the "dance" honeybees use to communicate the location of flowers (1940)
• George Wells Beadle and Edward Lawrie Tatum prove the "one gene, one enzyme" hypothesis using induced mutations in bread mold, Neurospora crassa (1941)
• Luria-Delbruck experiment demonstrates that in bacteria, beneficial mutations arise in the absence of selection, rather than being a response to selection. (1943)
• Barbara McClintock breeds maize plants for color, which leads to the discovery of transposable elements or jumping genes. (1944)
• Linus Pauling and colleagues show that a human genetic disease, sickle cell anemia, is caused by a molecular change in a specific protein, hemoglobin. (1949)
• Hershey-Chase experiment (by Alfred Hershey and Martha Chase) uses bacteriophage to prove that DNA is the hereditary material (1952)
• Miller-Urey experiment demonstrates that organic compounds can arise spontaneously from inorganic ones (1953)
• Meselson-Stahl experiment proves that DNA replication is semiconservative (1958)
• Crick, Brenner et al. experiment using frameshift mutations to support the triplet nature of the genetic code (1961)
• Nirenberg and Matthaei experiment with in vitro protein synthesis using synthetic RNA as to substitute for messenger RNA (1961).
• John Gurdon clones an animal, a frog tadpole, from an egg cell using the nucleus from an intestinal cell (1962).
• Roger W. Sperry shows the potential independence of the two sides of the human brain using split-brain patients (1962-1965)
• Nirenberg and Leder experiment, binding tRNA to ribosomes with synthetic RNA to decipher the genetic code (1964)
• Demonstration of the role of reverse transcriptases in tumor viruses, independently by Howard Temin and David Baltimore, 1970
• Herbert Boyer and Stanley Cohen selectively clone genes in bacteria, using bacterial plasmids cut by specific endonucleases (1975).
• Mary-Dell Chilton shows that crown gall tumors of plants are caused by the transfer of a small piece of DNA from the bacterium, Agrobacterium tumefaciens, into the host plant, where it becomes part of its genome (1977).
• Kary Mullis demonstrates the polymerase chain reaction, a method for amplifying specific bits of DNA (1983).
• Napoli, Lemieux and Jorgensen discover RNA interference (1990)

Chemistry

• Blaise Pascal caries a barometer up a church tower and a mountain to determine that atmospheric pressure is due to a column of air (1648).
• Robert Boyle uses an air pump to determine the inverse relationship between the pressure and volume of a gas. This relationship came to be known as Boyle's law (1660-1662).
• Joseph Priestley suspends a bowl of water above a beer vat at a brewery and synthesizes carbonated water (1767).
• Antoine Lavoisier determines that oxygen combines with materials upon combustion, thus disproving phlogiston theory (1783).
• Antoine Lavoisier determines that chemical reactions in a closed container do not alter total mass. From these observations he establishes the law of conservation of mass (1789).
• Benjamin Thompson, Count Rumford demonstrates that the heat developed by the friction of boring cannon is nearly inexhaustible. This result was presented in opposition to caloric theory (1798).
• Humphry Davy uses electrolysis to isolate elemental potassium, sodium, calcium, strontium, barium, magnesium, and chlorine (1807-1810).
• Joseph Louis Gay-Lussac studies reactions among gases and determines that their volumes combine chemically in simple integer ratios (1809).
• Robert Brown studies very small partices in water under the microscope and observes Brownian motion which was later named in his honor (1827).
• Friedrich Wöhler synthesizes the organic compound urea using inorganic reactants, disproving the application of vitalism to chemical processes (1828).
• Thomas Graham measures the rates of effusion for different gases and establishes Graham's law of effusion and diffusion (1833).
• Julius Robert von Mayer and James Prescott Joule measure the heat generated by mechanical work. This establishes the principle of conservation of energy and the kinetic theory of heat (1842-1843).
• Louis Pasteur separates a racemic mixture of two enantiomers by sorting individual crystals, and demonstrates their impact on the polarization of light (1849).
• Anders Jonas Ångström observes the presence of hydrogen and other elements in the spectrum of the sun (1862).
• François-Marie Raoult demonstrates that the decrease in the vapor pressure and freezing point of liquids caused by the addition of solutes is proportional to the number of solute molecules present. This establishes the concept of colligative properties (1878).
• Henri Louis Le Chatelier performs several experiments to disturb a chemical equilibrium before formulating Le Chatelier's Principle (1884).
• Svante Arrhenius studies the conductivity of salt solutions and determines that salts dissociate into ions in water. (1884)
• Svante Arrhenius determines the impact of temperature on reaction rates and formulates the concept of activation energy. (1889)
• William Ramsay and Lord Rayleigh (John Strutt) isolate the noble gases (1894-1898).
• Mikhail Tsvet (Mikhail Semyonovich Tsvet) separates chlorophyll from other plant pigments using chromatography (1901).
• Frederick Soddy and William Ramsay observe the production of helium (from alpha particles during radioactive decay (1903).
• Lise Meitner, Otto Hahn and Fritz Strassmann observe nuclear fission (1938).
• Glenn Theodore Seaborg creates and isolates five transuranium elements. He reorganizes the periodic table to its current form. (1941-1950).
• Melvin Calvin and Andrew Benson delineate the path of carbon in photosynthesis using Chlorella and carbon dioxide labeled with carbon-14 (¹⁴CO₂) (1945) - (1954).
• 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 to the discovery of 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.
• Harold Kroto, James Heath, Sean O'Brien, Robert Curl and Richard Smalley isolate buckyballs and other fullerenes (1985).

Physics

• Archimedes, while sitting in a bathtub, notices that his body becomes lighter as it pushes the water aside. This leads to the first true theory of buoyancy. (c. 250 BC)
• Eratosthenes evaluates the diameter of the Earth by comparing the length of the longest shadow of the day with the distance between that location and a place where the sun shines to the bottom of the well at midday (240 BC)
• Galileo Galilei uses rolling balls to disprove the Aristotelian theory of motion (1602 - 1607)
• Isaac Newton decomposes sunlight with a prism.
• Ole Rømer uses the timing of the eclipses of the moons of Jupiter with respect their distance from earth to estimate the speed of light for the first time. He yields a value of 225,000 km/s (actual value of 299,792 km/s) (1672)
• Henry Cavendish's torsion bar experiment (1798)
• Thomas Young's double-slit experiment (c1805)
• Hans Christian Ørsted discovers the connection of electricity and magnetism by experiments involving a compass and electric circuits (1820)
• Christian Doppler arranges to have trumpets played from a passing train. The ground-observed pitch was higher than that played when the train was approaching then lower than that played as the train passed and moved away, demonstrating the Doppler effect (1845)
• Léon Foucault's namesake Foucault pendulum is first exhibited. It demonstrates the Coriolis effect and the rotation of the earth (1851)
• Michelson-Morley experiment exposes weaknesses of the prevailing variant of the theory of luminiferous aether. (1887)
• Guglielmo Marconi demonstrates that radio signals can travel between two points separated by an obstacle. Marconi's servant is behind a hill 3 kilometers away and fires his rifle upon receiving the signals (1895).
• Henri Becquerel, Marie Curie, and Pierre Curie discover radioactivity and describe its properties. (1896)
• Joseph John Thomson's cathode ray tube experiments (discovers the electron and its negative charge) (1897)
• Robert Millikan's oil-drop experiment, which suggests that electric charge occurs as quanta (whole units), (1909)
• Heike Kamerlingh Onnes demonstrates superconductivity (1911)
• Ernest Rutherford's gold foil experiment demonstrated that the positive charge and mass of an atom is concentrated in a small, central atomic nucleus, disproving the then-popular plum pudding model of the atom (1911)
  • Arthur Eddington leads an expedition to the island of Principe to observe a total solar eclipse (gravitational lensing). This allows for an observation of the bending of starlight under gravity, a prediction of Albert Einstein's theory of relativity. It was confirmed (although it was later shown that the margin of error was as great as the observed bending) (1919)
  • Otto Stern and Walter Gerlach conduct the Stern-Gerlach experiment, which demonstrates particle spin (1920)
  • Enrico Fermi splits the atom (1934, although the results were not fully understood until 1939, by Otto Hahn and Fritz Strassmann)
  • Enrico Fermi builds the first critical nuclear reactor (1942)
  • John Bardeen and Walter Brattain fabricate the first working transistor (1947)
  • Clyde L. Cowan and Frederick Reines confirm the existence of the neutrino in the neutrino experiment (1955)
  • The Scout rocket experiment confirms the time dilation effect of gravity. (1976)
  • A team at CERN discovered the W and Z bosons, providing direct experimental evidence for the Electroweak theory, and adding further weight to the Standard Model of Particle Physics (1983)
  • Eric A. Cornell and Carl E. Wieman synthesize Bose-Einstein condensate at the University of Colorado at Boulder (1995)

  Psychology

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  • Ivan Pavlov's experiments with dogs and classical conditioning (1900s)
  • John B. Watson and Rosalie Rayner conduct the Little Albert experiment showing evidence of classical conditioning (1920)
  • Solomon Asch's conformity experiments shows how group pressure can persuade an individual to conform to an obviously wrong opinion (1951)
  • B.F. Skinner's demonstrations of operant conditioning (1930s - 1960s)
  • Harry Harlow's experiments with baby monkeys and wire and cloth surrogate mothers (1957-1974)
  • Stanley Milgram's experiments on human obedience (1963)
  • Philip Zimbardo's Stanford prison experiment (1971)
  • Allan and Beatrice Gardner' attempts to teach American Sign Language to the chimpanzee Washoe (1970s)
  • Martin Seligman studies learned helplessness in dogs (1970s)
  • Rosenhan experiment (1972)
  • Kansas City preventive patrol experiment (1972-1973)
  • Elizabeth Loftus' and John C. Palmer's car crash experiment shows that leading questions can produce false memories (1974)

  Economics and Political Science

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  • Robert Axelrod's Prisoner's Dilemma computer tournaments, later documented in The Evolution of Cooperation

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