On the left is the view of the travel path of a droplet that is buffeted by the air molecules as shown on the right.

Brownian Motion

 

In 1827, the British botanist Robert Brown was investigating pollen grains in water, and noticed that they wouldn't sit still under his microscope. Experiments by Brown and others showed that the motion is more rapid and the particles (droplets) move farther in a given time interval when the temperature of suspending matter (e.g. air) is raised, when the viscosity (resistance to flow) of the fluid is lowered, or when the

size of the droplets is reduced.

Albert Einstein in 1905 arrived at a mathematical explanation of Brownian Motion and integrated it into kinetic theory.