agrāhyaṃ vāyvādi yasmān mahatvam anekadravyavatvaṃ rūpasamavāyādiścopalabdhikāraṇamiṣyate tac ca vāyvādau nāsti
"Imperceptible" refers to air and other [substances], because largeness, possession of multiple substances, inherence of color and other [qualities] are considered to be causes of perceptibility, and these do not exist in air and other [substances].