Used with
permission of Maiken Naylor, University at Buffalo, Buffalo, NY, USA,
http://ublib.buffalo.edu/libraries/units/sel/exhibits/stamps
Democritus (460-370 BC) was a Greek philosopher who advanced the theory that all matter consisted of tiny, indivisible and also invisible particles called atoms. These atoms are in constant motion and have properties that explain the physical characteristics of substances. They are eternal and cannot be created or destroyed. While this theory was discredited in Aristotelian thought, modern physics proved it accurate, though with many modifications: although atoms as building blocks of matter determine the characteristics of substances, they themselves are made up of even smaller subatomic particles.