SB 3.11.5
anur dvau paramanu syat
trasarenus trayah smrtah
jalarka-rasmy-avagatah
kham evanupatann agat
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The division of gross time is calculated as follows: two atoms make one double atom, and three double atoms make one hexatom. This hexatom is visible in the sunshine which enters through the holes of a window screen. One can clearly see that the hexatom goes up towards the sky.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The atom is described as an invisible particle, but when six such atoms combine together, they are called a trasarenu, and this is visible in the sunshine pouring through the holes of a window screen.