Vāyu said: Paramāṇu (Atom) is very subtle. It can be mentally conceived but it cannot be seen by the eyes. What cannot be further broken up in the world should be known as Paramāṇu (atom). When the rays of the sun come through the window, minute dust particles are seen. The learned men call that particle a Paramāṇu. It is the first in the series of units of measurement.