Śatapatha Brāhmaṇa ("of a hundred paths") 8.3.2.1

8.3.2.1

atha viśvajyotiṣamupadadhāti | vāyurvai madhyamā viśvajyotirvāyurhyevāntarikṣaloke viśvaṃ jyotirvāyumevaitadupadadhāti tāmanantarhitāṃ diśyābhya upadadhāti dikṣu tadvāyuṃ dadhāti tasmātsarvāsu dikṣu vāyuḥ

He then lays down a Visvagyotis (all-light brick). Now the middle Visvagyotis is Vâyu, for Vâyu (the wind) is all the light in the air-world: it is Vâyu he thus places therein. He places it so as not to be separated from the regional (bricks): he thus places Vâyu in the regions, and hence there is wind in all the regions.