Verse 3.18.4

प्राण एव ब्रह्मणश्चतुर्थः पादः स वायुना ज्योतिषा भाति च तपति च् भाति च तपति च कीर्त्या यशसा ब्रह्मवर्चसेन य एवं वेद ॥ ३.१८.४ ॥

prāṇa eva brahmaṇaścaturthaḥ pādaḥ sa vāyunā jyotiṣā bhāti ca tapati c bhāti ca tapati ca kīrtyā yaśasā brahmavarcasena ya evaṃ veda || 3.18.4 ||

4. Prāṇa [the organ of smelling] is one of the four feet of Brahman [as the mind]. It shines by the light of vāyu [air] and also radiates heat. He who knows this shines and radiates warmth with his good work, with his fame, and with the radiance he acquires from leading a scholarly and disciplined life.

Word-for-word explanation:

Prāṇaḥ eva brahmaṇaḥ caturthaḥ pādaḥ, prāṇa [the organ of smelling] is the fourth foot of [manomaya] Brahman; vāyunā jyotiṣā, by the light it gets from air [its presiding deity]; saḥ bhāti ca tapati ca, it shines and gives heat; yaḥ evam veda, he who knows thus; bhāti ca tapati ca, shines and radiates warmth; kīrtyā, through good work; yaśasā, through fame; brahmavarcasena, through the radiance that comes from a scholarly and disciplined life.

Commentary:

Vāyu, air, is the presiding deity of the organ of smell, because vāyu carries odours and reveals them.