"The men of that time (the Aryas) perceived that all the movements of inanimate things which take place on the earth's surface proceed from heat, which manifests itself, either under the form of fire which burns, or under the form of thunder, or under the form of wind; but the thunder is fire hidden in the cloud, and rises with it into the air;--fire which burns is, before it manifests itself, shut up in the vegetable matters which supply it with aliment; wind is produced when the air is stirred by heat, which rarefies it or condenses it on its withdrawal. "Vegetables, in their turn, derive their combustibility from the sun, which makes them grow, by storing up his heat in them, and the air is warmed by the rays of the sun, the same rays which reduced the terrestrial waters to invisible vapours, and then to thunder-bearing clouds. The clouds spread the rain, make the rivers, feed the sea which the agitated winds trouble. Thus all this mobility which animates nature around us is the work of heat, and heat proceeds from the sun, which is at the same time "the celestial traveller," and the universal motor. "Life also seemed to them to be closely allied to the idea of fire. The grand phenomenon of the accumulation of solar heat in plants, a phenomenon which science has since elucidated, was early perceived by the ancients. It is frequently pointed out in the Veddas in expressive terms. When they lighted the wood on the hearth they knew that they only 'forced' it to give out the fire which it had received from the sun. When their attention was directed to animals, the close bond which exists between heat and life, struck them in all its force; heat maintains life, they found no living animals in whom was life without heat; on the contrary, they saw that vital energy displayed itself in the proportion in which the animals shared in heat, and diminished in the same proportion. Life exists and perpetuates itself on the earth on three conditions only, that fire should penetrate the body under its three forms, of which one resides in the sun's rays, one in the ignited aliments, and the third in respiration, which is air renewed by motion. Now these two latter proceed, each after its own fashion, from the sun (sûrya); his celestial force is the universal motor, and the father of life: that which he first engendered, is the fire here below (agni) born of his rays, and his second eternal co-operator is air put in motion, which is also called wind, or spirit (vâyu)."[9] The worship of the sun still exists among all the negro tribes which inhabit the interior of Africa; it may even be said that it is the only religion of the African tribes, and this religion has existed among them in all times.