As man, however, began to read nature aright, and as his moral and intellectual faculties were developed, it was necessary that the solar deities themselves should become invested with co-relative attributes, or that other gods should be formed to embody them. The perception of _light_, as distinguished from heat, was a fertile source of such attributes. In the Chaldean mythology, _Vul_, the son of _Anu_, was the god of the air, but his power had relation to the purely atmospheric phenomena rather than to light.[156] The only reference to light found in the titles of the early deities is in the character ascribed to _Va-lua_, the later _Bur_ or _Nin-ip_, who is said to “irradiate the nations like the sun, the light of the gods.”[157] But this deity was apparently the distant planet Saturn, if not originally the moon, and the perception of light as a divine attribute must be referred to the Aryan mind.[158] Thus the Hindu _Dyaus_ (the Greek _Zeus_) is the shining deity, the god of the bright sky. As such the sun-gods now also become the gods of intellectual wisdom, an attribute which also appears to have originated with the Aryan peoples, among whom the Brahmans were possessors of the highest wisdom, as children of the sun, and whose Apollo and Athené were noble embodiments of this attribute. The Chaldean gods, _Héa_ and _Nebo_, were undoubtedly symbolised by the wedge or arrow-head, which had especial reference to learning. In reality, however, this symbol merely shows that they were the patrons of letters or writing, and not of wisdom, in its purely intellectual aspect. If the form of the Assyrian alphabetical character was of Phallic origin,[159] we may have here the source of the idea of a connection between physical and mental knowledge embodied in the legend of the “fall.” In the Persian _Ahurô-mazdâo_ (the wise spirit) we have the purest representation of intellectual wisdom. The book of Zoroaster, the Avesta, is literally the “word,” the word or wisdom which was revealed in creation and embodied in the divine Mithra, who was himself the luminous sun-god.