This abr?g? of Jacob's 2005 study Atman: A Reconstruction of the Solar Cosmology of the Indo-Europeans (Hildesheim: Georg Olms) focuses on the cosmological insights that inform ancient Indo-European religions and, in particular, on the most significant trinity worshipped by the ancient Indo-Aryans - Agni-Vayu-Aditya - which represents the forms that the cosmic fire takes in the underworld of Earth before it is installed as the sun in the Heaven of our universe. This is not a sociological Trinity, as Dum?zil's studies, for example, would lead one to believe. Rather, it is an understanding of the divine fire that informs the macrocosm as well as the human microcosm. The present essay should thus serve to correct the misleading sociological orientations of Dum?zilian comparative mythology. At the same time, it will give the reader a glimpse into the extraordinary depth of vision of the prisca theologia of the Indo-Europeans.