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 hurts the geocentric model of the cosmos (1609)
• Arno Penzias and Robert Wilson detect the cosmic microwave background radiation, giving support to the theory of the Big Bang (1964)

Biology

• Anton van Leeuwenhoek discovers microorganisms
• Robert Hooke, using a microscope, observes cells (1665)
• Edward Jenner tests the first vaccine (1796)
• Gregor Mendel's pea plant experiments lead him to surmize many of the fundamental theories 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) A continuation of the rancid meat experiment done by Francesco Redi
• Frederick Griffith demonstrates (Griffith's experiment) that living cells can be transformed via a transforming principle, later discovered to be DNA (1928)
• Karl von Frisch decodes the "dance" honeybees use to communicate the location of flowers (1940)
• 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 jumping genes (1944)
• Hershey-Chase experiment 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 (1961)
• Nirenberg and Matthaei experiment (1961)
• Nirenberg and Leder experiment (1964)

Chemistry

• Neil Bartlett mixes xenon and fluorine leading to the first synthesis of a noble gas compound, xenon tetrafluoride (1962)

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 lengthiest 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 force 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 discovers radioactivity (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)
• John Bardeen and Walter Brittain 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)
• Stanley Pons and Martin Fleischmann report the production of excess heat from a table-top cold fusion experiment (1989)
• Eric A. Cornell and Carl E. Wieman synthesize Bose-Einstein condensate (1995)

Psychology

• 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

• Negative Income Tax experiments
• Axelrod's Prisoner's Dilemma Tournament
• Tennessee STAR Class Size Experiment