"The higher gods of the Rgveda are almost entirely personifications of natural phenomena, such as Sun, Dawn, Fire, Wind. Excepting a few deities surviving from an older period, the gods are, for the most part, more or less clearly connected with their physical foundations. The personifications being therefore but slightly developed, lack definiteness of outline and individuality of character. Moreover, the phenomena themselves which are behind the personifications have few distinctive traits, while they share some attributes with other phenomena belonging to the same domain. Thus Dawn, Sun, Fire have the common features of being luminous, dispelling darkness, appearing in the morning. ... The universe appeared to the poets of the Rgveda to be divided into three domains of earth, air, and heaven, ... This is the favourite triad of the Reveda, constantly mentioned expressly or by implication. The solar phenomena are referred to heaven, while those of lightning, rain, and wind belong to the air. In the three worlds the various gods perform their actions, though they are supposed to dwell only in the third, the home of light."