The problem which occupied the powerful intellects of Hume and Kant, and which these philosophers named the principle of causality, was already exercising the brains of our fathers when they gave names for the first time to the sky, the sun, the dawn, and the other physical phenomena, by means of roots indicating activity; for the principle of causality manifested itself in the beginning, not in the direct search for a cause, but in the assertion of the existence of an agent. This mental labour, commenced and accomplished thousands of centuries ago by millions of human beings, deserves at least as much attention from us as the learned speculations of two modern philosophers, be they Hume or Kant. So striking an object as the sun, even before possessing a definite name, must have been designated in some special way; perhaps as a simple circle, such as we find in the Egyptian hieroglyphics, in the Chinese writing, and in our astronomical almanacs; this symbol would give little opportunities to the mythologists; but when the idea arose that the sun was a ball, and that an analogy was found between a ball and an eye, man began to speak of the sun as the eye of the sky. We say readily in all languages, “God is omniscient,” but Hesiod, to express the same truth said, “The sun is the eye of Zeus who sees and knows all.” If the language appears childish to us, we must remember that it was the expression of a poet who lived long before the philosophers of Greece, we shall then be less struck by its harshness than by the happy and pure thought which has been expressed. The sun has been an object of adoration with many of the primitive nations; it seems uncertain whether as the divinity himself or as his representative; most of the mythologists assure us that the ancient Egyptians worshipped the sun’s disc itself. The first step is invariably followed by a second, and a good example of development in religious belief is afforded by a Mexican legend. The story is told of the Inca Tupac Yupanqui, who, though reputed a son of the sun, began to doubt the divine omnipotence of his divine ancestor. At a great religious council, held at the consecration of the newly built temple of the sun at Cuzco, he rose before the assembled multitude to deny the divinity of the sun. “Many say,” he began, “that the sun is the maker of all things. But he who makes should abide by what he has made. Now many things happen when the sun is absent; therefore he cannot be the universal Creator. And that he is alive at all, is doubtful, for his journeys do not tire him. He is like a tethered beast who makes a daily round; he is like an arrow which must go whither it is sent, not whither it wishes. I tell you that he, our father and maker--the sun--must have a lord and master more powerful than himself, who constrains him to his daily circuit without pause or rest.”[95]