As in the conflict raging in the sky during gale or tempest, when the light and the darkness alternately prevail, the barbaric mind sees war waged between the heroes of the spirit-land who have carried their unsettled blood feuds thither, so in many myths the lightning is no comrade of the thunder, but its foe, the battle of bird with serpent. The resemblance of the lightning flash to the sharp, sudden, zigzag movements of the serpent, a creature so mysterious to barbaric man in its unlikeness to the beasts of the field, accounts for a myth the influence of which as a terrorising agent on human conduct is in course of rapid decay. Its importance in the history of belief in the supernatural is too far-reaching to be passed over, and in tracing its course it is necessary to show its connection with the group of storm-myths and sun-myths of the Aryan race in the battles between Indra and Vritra, Ormuzd and Ahriman, Thor and Midgard, Hercules and Cacus, Apollo and Pythôn, and St. George and the Dragon.
All the Aryan nations have among their legends, often exalted into epic themes, the story of a battle between a hero and a monster. In each case the hero conquers, and releases treasures, or in some way renders succour to man, through his victory. In Hindu myth this battle is fought between Indra and Vritra.
Indra, one of the Vedic gods, comes, according to Professor Max Müller, from the same root as the Sanskrit _indu_, drop, sap, but the etymology is doubtful. What is not doubtful is that he is the god of the bright sky, and although, like the other gods invoked in the hymns of the _Rig-Veda_, a departmental or tribal deity, he is a sort of _primus inter pares_, of whose many titles, Vritrahan or "Vritra-slayer" is the pre-eminent one. The benefits showered by him upon mortals caused the attribution of moral qualities to him, and he was adored as "lord of the virtues," while the juice of the sacred soma plant was offered in his honour, for which reason he is also called Somapâ or "soma-drinker." It is his struggle with Vritra which is a constant theme of the Vedic hymns, the burden of which remind us of the praises offered in the Psalms to Yahweh as a man of war, as mighty in battle. "The gods do not reach thee, nor men, thou overcomest all creatures in strength.... Thou thunderer, hast shattered with thy bolt the broad and massive cloud into fragments, and has sent down the waters that were confined in it to flow at will; verily thou alone possessest all power." The primitive physical meaning of the myth is clear. Indra is the sun-god, armed with spears and arrows, for such did the solar rays sometimes appear to barbaric fancy. The rain-clouds are imprisoned in dungeons or caverns by Vritra, the "enveloper," the thief, serpent, wolf, wild boar, as he is severally styled in the _Rig-Veda_. Indra attacks him, hurls his darts at him, they pierce the cloud-caverns, the waters are released, and drop upon the earth as rain.