Ancient philosophers were curious about the structure of substances. The Greeks first put forward the idea atoms. The idea was not based on any experimental facts. To the ancient Greek philosophers, the problem of the structure of the substances presented itself as a mere choice between two alternatives. Substances are either continuous or discrete.

Democritus (460 - 370 B.C) thought that substances are made up of tiny indivisible particles. If a piece of copper is cut into smaller and smaller pieces one finally reaches a point where it can no longer be divided. He called these particles atoms. The word atom has its origin from the Greek word “Atomos” which means indivisible.

On the other hand Aristotle (384 – 322 B.C) argued that matter is continuous. According to Aristotle and his followers, there was no particle of matter so small that it could not be subdivided into still smaller pieces. Table 1 shows the comparison between the discrete and continuous theory of matter.