SB 3.11.5

aṇur dvau paramāṇū syāt
 trasareṇus trayaḥ smṛtaḥ
jālārka-raśmy-avagataḥ
 kham evānupatann agāt
Synonyms: 
aṇuḥ — double atom; dvau — two; parama-aṇu — atoms; syāt — become; trasareṇuḥ — hexatom; trayaḥ — three; smṛtaḥ — considered; jāla-arka — of sunshine through the holes of a window screen; raśmi — by the rays; avagataḥ — can be known; kham eva — towards the sky; anupatan agāt — going up.
Translation: 
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: 

The atom is described as an invisible particle, but when six such atoms combine together, they are called a trasareṇu, and this is visible in the sunshine pouring through the holes of a window screen.