mṛdutvaṁ kaṭhinatvaṁ ca
śaityam uṣṇatvam eva ca
etat sparśasya sparśatvaṁ
mṛdutvam—softness; kaṭhinatvam—hardness; ca—and; śaityam—cold; uṣṇatvam—heat; eva—also; ca—and; etat—this; sparśasya—of the subtle element touch; sparśatvam—the distinguishing attributes; tat-mātratvam—the subtle form; nabhasvataḥ—of air.
Softness and hardness and cold and heat are the distinguishing attributes of touch, which is characterized as the subtle form of air.
Tangibility is the proof of form. In actuality, objects are perceived in two different ways. They are either soft or hard, cold or hot, etc. This tangible action of the tactile sense is the result of the evolution of air, which is produced from the sky.
Link to this page: https://prabhupadabooks.com/sb/3/26/36