Robert P. Crease, a member of the philosophy department at the State University of New York at Stony Brook and the historian at Brookhaven National Laboratory, recently asked physicists to nominate the most beautiful experiment of all time.
The results were:
1. Double-slit electron diffraction - Showed Electrons have wavelike properties.
2. Galileo's Tower of Pisa Experiment - Showed that objects fall at the same rate, regardless of mass.
3. Millikan's oil-drop experiment - Determined the fundamental charge unit, the charge of an electron.
4. Newton's Prism - Showed White light made up of colored light.
5. Young's Interference Experiment - Showed that light has wavelike properties.
6. Cavendish's torsion-bar experiment - Measured the value of the gravitational constant (G).
7. Eratosthenes' Experiment - Measured the circumference of the earth, in 276 BC.
8. Galileo's Inclined Plane Experiment - Demonstrated that distance travelled by a ball rolling down an incline plane is proportional to the square of the time.
9. Rutherford's discovery of the nucleus- Discovered atoms consist of a small nucleus surrounded by electrons.
10. Foucault's Pendulum - Demonstrated that the Earth rotates.
I think the pendulum was pretty cool. I wasn't aware of the Galileo one, I guess that really set the table for Newton.