Brownian Motion

grains suspended in water jiggled about under the lens of the

microscope, following a zigzag path such as the picture on page

three. Brown had discovered what is now known as Browian motion

or Browian movement. Even more remarkable was the fact that

pollen grains that had been stored for a century moved in the same

way. The motion appeared to be totally random and at first Brown

thought that he had discovered the “primitive molecule”. That is

until he observed the same motion in dusty particles of inorganic

matter. Many people tried to master the concept of Brownian

movement and had to go through some testy times. In 1889, G.L.

Gouy found that the "Brownian" movement was more rapid for

smaller particles. For example, we do not observe Brownian motion

in cars, buildings, or people. In 1900, F.M. Exner undertook the

first quantitative studies, measuring how the motion depended on

temperature and particle size. And he found that the speed of

movement increased with a rise in temperature, but then, it

decreased if bigger particles were used in the observation.

The first truly reasonable explanation of Brownian movement

horizontal displacement during the time t increases in proportion

jump. These small random jumps are what make up Brownian

comes to rest if not impelled by some external force.

whatever, it is possible to prove that the mean displacement of a

As for Perrin, his view was that Einstein and Marian

The following is the beginning paragraph of this famous paper:

Some topics in this essay:
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