The oldest among the gods of heaven is Dyaus (identical with the Greek Zeus). This personification of the sky as a god never went beyond a rudimentary stage in the Rigveda, being almost entirely limited to the idea of paternity. Dyaus is generally coupled with Prithivi, Earth, the pair being celebrated in six hymns as universal parents. In a few passages Dyaus is called a bull, ruddy and bellowing downwards, with reference to the fertilising power of rain no less than to the lightning and thundering heavens. He is also once compared with a black steed decked with pearls, in obvious allusion to the nocturnal star-spangled sky. One poet describes this god as furnished with a bolt, while another speaks of him as "Dyaus smiling through the clouds," meaning the lightening sky. In several other passages of the Rigveda the verb "to smile" (smi) alludes to lightning, just as in classical Sanskrit a smile is constantly compared with objects of dazzling whiteness. A much more important deity of the sky is Varuna, in whom the personification has proceeded so far that the natural phenomenon which underlies it can only be inferred from traits in his character. This obscurity of origin arises partly from his not being a creation of Indian mythology, but a heritage from an earlier age, and partly from his name not at the same time designating a natural phenomenon, like that of Dyaus. The word varuna-s seems to have originally meant the "encompassing" sky, and is probably the same word as the Greek Ouranos, though the identification presents some phonetic difficulties. Varuna is invoked in far fewer hymns than Indra, Agni, or Soma, but he is undoubtedly the greatest of the Vedic gods by the side of Indra. While Indra is the great warrior, Varuna is the great upholder of physical and moral order (rita). The hymns addressed to him are more ethical and devout in tone than any others. They form the most exalted portion of the Veda, often resembling in character the Hebrew psalms. The peaceful sway of Varuna is explained by his connection with the regularly recurring celestial phenomena, the course of the heavenly bodies seen in the sky; Indra's warlike and occasionally capricious nature is accounted for by the variable and uncertain strife of the elements in the thunderstorm. The character and power of Varuna may be sketched as nearly as possible in the words of the Vedic poets themselves as follows. By the law of Varuna heaven and earth are held apart. He made the golden swing (the sun) to shine in heaven. He has made a wide path for the sun. The wind which resounds through the air is Varuna's breath. By his ordinances the moon shining brightly moves at night, and the stars placed up on high are seen at night but disappear by day. He causes the rivers to flow; they stream unceasingly according to his ordinance. By his occult power the rivers swiftly pouring into the ocean do not fill it with water. He makes the inverted cask to pour its waters and to moisten