In northern latitudes winter is distinctly the _dark_ season; in tropical India there is little or no perceptible difference between the darkness of winter and summer. But in India winter is distinctly the dry season. Midsummer is the all-important season of the rains. Indra’s conquest over Vritra, or the arrival of solstitial rains, marked by the disappearance of the constellation Hydra from the sky, was mythologically in the Vedas described as Indra’s conquest over the demon of _drought_, but still traditionally--for the power of tradition is great--even in India Indra retained the attributes of the conqueror over the demon of _darkness_. [Illustration: PLATE X. Portion of Sun at Summer Solstice, 3,000 B.C. Observer in Lat. 23° N. Constellations between the lines H H Z and Z H H invisible all through the night of Summer Solstice. [_To face p. 121._] At Plate X. a drawing is given of the southern heavens and of the constellations--invisible at midsummer and visible at midwinter, above the horizon of an observer in latitude 23° N. at the date 3000 B.C., a thousand years later than the date referred to in Plate IX. For reasons which will appear more clearly when we come to the discussion of the Soma myth, it is to about this date that I would attribute the composition of many of the Vedic hymns. But if Indra is to be considered as representing the summer solstice, and Vritra as representing the constellation Hydra, we must surely expect some astronomic interpretation for Soma--Soma by which the mighty Indra is invigorated and enabled to triumph gloriously over the demon. According to non-astronomic explanations, “the concrete terrestrial plant and the intoxicating juice extracted therefrom” are considered to be the basis of the mythology of Soma. It is admitted that in post-Vedic literature Soma is a regular name of the moon, which is regarded as being drunk up by the gods, and so waning. Some writers point to the possibility that even in the Rig Veda, “in the Soma hymns there may occasionally lurk a veiled identification of ambrosia and the moon, ... but on the whole, with the few exceptions generally admitted, it appears to be certain that to the seers of the Rig Veda the god Soma is a personification of the terrestrial plant and juice.”[60] [60] Macdonell, _Vedic Mythology_, p. 113. One German writer, Hillebrandt, very strongly upholds the view that Soma in the Rig Veda “often personifies the moon,”[61] and especially according to him is this the case in the 114 hymns of Maṇḍala IX., all addressed to Soma pavamāna, or “purified Soma,” prepared for and quaffed by Indra to invigorate him for the Vritra combat. [61] _Vedic Mythology_