Another passage where the concept of the tapas plays a role occurs in the myth of the creator of the world, Prajâpati. In the beginning, he was alone. Apart from him there was nothing:
Pragâpati had the desire of creating beings and multiplying himself. He underwent (consequently) austerities.
Having finished them, he created these worlds, viz., earth, air and heaven. He heated them (with the lustre of his mind, pursuing a course of austerities); three lights were produced:
Agni from the earth, Vayu from the air, and Aditya from heaven.
He heated them again, in consequence of which the three Vedas were produced.
This means “he heated himself with his own heat,” in commutatio. “He brooded, he hatched.” He incubates himself.
This is the word used for the technical concentration exercises out of which yoga developed. ~Carl Jung, Psychology of Yoga and Meditation, Page 10