Positions of the Sun: Roy states that 'Visnu's three strides alluded to in the Rigveda have been variously interpreted as meaning the three different positions of the sun at his rising, culmination, and setting. It is interesting to note in this connection the etymological explanation of the terms, Vamana and Visnu given in the puranas. Visnu is so-called from the verbal root vis. meaning 'to enter' or 'to pervade' because he, in his dwarf form, has pervaded or penetrated everything. A similar idea is also found in the Upanisad, where the soul is described as of the size of a thumb, always seated in everyone's heart'.