Hydromancy is a method of divination by means of water, including the color, ebb and flow, or ripples produced by pebbles dropped in a pool.

The Jesuit M. A. Del Rio (1551–1608) described several methods of hydromancy. The first method described depicts a ring hanging by a string that is dipped into a vessel of water which was shaken. A judgment or prediction is made by the number of times which the ring strikes the sides of the vessel.

A second method is when three pebbles are thrown into standing water and observations are made from the circles formed when the objects strike the water.

The third method described depended upon the agitation of the water, this custom was prevalent among Oriental Christians of annually baptizing that element.

A fourth method used colors of the water and figures appearing in it. Varro stated that many prognostications were made in this way concerning the Mithridatic War. This branch of the divination proved so important that it was given a separate name and there arose from it the divination of fountains whose waters were frequently visited.

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