Many myths are told about the Açvins as succouring divinities. They deliver from distress in general, especially rescuing from the ocean in a ship or ships. They are characteristically divine physicians, who give sight to the blind and make the lame to walk. One very curious myth is that of the maiden Viçpala, who having had her leg cut off in some conflict, was at once furnished by the Açvins with an iron limb. They agree in many respects with the two famous horsemen of Greek mythology, the Dioskouroi, sons of Zeus and brothers of Helen. The two most probable theories as to the origin of these twin deities are, that they represent either the twilight, half dark, half light, or the morning and evening star. In the realm of air Indra is the dominant deity. He is, indeed, the favourite and national god of the Vedic Indian. His importance is sufficiently indicated by the fact that more than one-fourth of the Rigveda is devoted to his praise. Handed down from a bygone age, Indra has become more anthropomorphic and surrounded by mythological imagery than any other Vedic god. The significance of his character is nevertheless sufficiently clear. He is primarily the thunder-god, the conquest of the demon of drought or darkness named Vritra, the "Obstructor," and the consequent liberation of the waters or the winning of light, forming his mythological essence. This myth furnishes the Rishis with an ever-recurring theme. Armed with his thunderbolt, exhilarated by copious draughts of soma, and generally escorted by the Maruts or Storm-gods, Indra enters upon the fray. The conflict is terrible. Heaven and earth tremble with fear when Indra smites Vritra like a tree with his bolt. He is described as constantly repeating the combat. This obviously corresponds to the perpetual renewal of the natural phenomena underlying the myth. The physical elements in the thunderstorm are seldom directly mentioned by the poets when describing the exploits of Indra. He is rarely said to shed rain, but constantly to release the pent-up waters or rivers. The lightning is regularly the "bolt," while thunder is the lowing of the cows or the roaring of the dragon. The clouds are designated by various names, such as cow, udder, spring, cask, or pail. They are also rocks (adri), which encompass the cows set free by Indra. They are further mountains from which Indra casts down the demons dwelling upon them. They thus often become fortresses (pur) of the demons, which are ninety, ninety-nine, or a hundred in number, and are variously described as "moving," "autumnal," "made of iron or stone." One stanza (x. 89, 7) thus brings together the various features of the myth: "Indra slew Vritra, broke the castles, made a channel for the rivers, pierced the mountain, and delivered over the cows to his friends." Owing to the importance of the Vritra myth, the chief and specific epithet of Indra is Vritrahan, "slayer of Vritra." The following stanzas are from