Click on the Green Flag. The opening screen displays a diagram recorded in a 1909 experiment by Jean Perrin—a French physicist and chemist—and an assistant. The diagram shows three paths of a a single particle as observed under a microscope. The path on the left shows the track of the particle as recorded at 30-second intervals for 24 minutes. The middle track as recorded at 30-second intervals for 25 minutes and the right track for 20 minutes (also at 30-second intervals). Measurements taken from this record validated experimentally Albert Einstein's theoretical formula for the diffusion of a particle in a liquid. This established the actual existence of atoms and molecules. Press 'Space' to clear the screen and this project simulates the motion (a random walk) of a single particle as observed by Perrin and an assistant in the 1909 experiment. See Notes and Credits.
In 1827 the English botanist Robert Brown was observing through a microscope small pollen particles in water. He observed that the particles moved through the water but he could not determine the mechanism that caused the motion. The molecular and atomic structure of matter had been theorized but there was no direct evidence that molecules and atoms actually existed. In 1905 Albert Einstein, not knowing of Brown’s observations, published a paper that explained how the motion that Brown had observed was the result of the particles of pollen being bombarded on all sides by water molecules. At different times the particle is hit more on one side than another, leading to the seemingly random nature of the motion. Einstein’s paper offered the first theoretical argument that molecules and atoms actually existed and were not just conceptual models. The 1909 experiment of Perrin validated Einstein's 1905 formula. Resources: The Fractal Geometry of Nature by Benoit Mandelbrot https://uwaterloo.ca/chem13news/sites/ca.chem13news/files/uploads/files/may06_2006_page_14.pdf http://userpages.umbc.edu/~dfrey1/ench630/ein_ran_walk.pdf
