Live Fire

 When the Shiv-ling is placed under a pitcher (containing libation) from which the liquid slowly and continuously drips over it, there is a semblance of celebration of an uninterrupted yajna even when there is no worshipper present. Solid ling (or Shiv-ling) in that case represents the live fire (in yajna) and the pitcher (with dripping libation) symbolizes the worshipper pouring oblations into the fire. It is a simulation of the Vedic yajna even without lighting a fire; and it involves basically the worship of a ling (Shiv-ling) representing the deity Agni (as related to a yajna). This substitution of the solid image (ling) for a real flame long ago transformed various rituals and worships making them quite simple and easy. Moreover, it is clear that fire -- in actual form (as a flame) or symbolically (as a ling or image of flame) -- has been an integral part of Vedic (Hindu) yajnas (worships) for a long time whether or not the service is dedicated to Agni.