The first of these theories was that of _solar attraction_. We have already described the doctrine, certainly of eastern origin, that the sun by a series of emissions and absorptions projected souls onto the earth and drew them back to itself.[395] This unceasing action of the resplendent luminary of day was exercised through the force of its rays,[396] and very old Greek ideas here mingled with the “Chaldean” theory. The Pythagoreans already believed that the glittering particles of dust which danced ceaselessly in a sunbeam (ξύσματα) were souls descending from the ether borne on the wings of light. The air, they said, was “full of souls,” we might say “of germs” or “microbes.”[397] They added that this sunbeam, passing through the air and through water down to the depths of the sea, gave life to all things below.[398] This idea persisted under the Roman Empire in the theology of the mysteries. Souls descended upon the earth and reascended after death towards the sky, thanks to the slanting rays of the sun which served as the means of transport. The sun is the ἀναγωγεύς, “he who brings up from below.” On Mithraic reliefs one of the seven rays which surround the head of Sol Invictus (θεὸς ἑπτάκτις) is seen disproportionately prolonged towards the dying Bull, in order to awake the new life that is to spring from the death of the cosmogonic animal. “The Sun,” says the Emperor Julian, “by the invisible, immaterial, divine and pure essence which dwells in its rays, attracts and raises the blessed souls.”[399] In this theory it is to the power of the Sun, the great cosmic divinity, that the ascension of the soul is due. According to another doctrine the cause of this ascension is the physical nature of the soul. This latter doctrine is set forth with great precision by Cicero in the Tusculan Disputations, and by Sextus Empiricus, doubtless after Posidonius.[400] The soul is a fiery breath, that is to say, its substance is the lightest of the four elements which compose our universe. It necessarily therefore has a tendency to rise, for it is warmer and more subtle than the gross and dense air which encircles the earth. It will the more easily cleave this heavy atmosphere since nothing moves more rapidly than a spirit. It must therefore in its continuous ascent pass through that zone of sky where gather the clouds and the rain and where blow the winds,[401] and which by reason of exhalations from the earth is moist and misty. When finally it reaches the spaces filled by an air which is rarefied and warmed by the sun, it finds elements similar to its own substance and, ceasing to ascend, is maintained in equilibrium.[402] Henceforth it dwells in these regions which are its natural home, continually vivified by the same principles as those that feed the everlasting fires of the stars. We shall presently see how the Platonists modified this Stoic doctrine, and substituted that of the “vehicle” (ὄχημα) of souls.