This is a technique used by the ancient Egyptian priests, for example, who stared into a bowl of water.
There is nothing present in the water, but the intense gazing arouses the soul into seeing something.
It has a hypnotic and fascinating effect.
For this purpose, the ancient magicians used a glass button or jewel, or Egyptian priests a beautiful blue crystal, in order to impart unconscious perceptions to their clientele.
It was not understood in this way back then but was employed for the purposes of prophecy, divination, and healing.
The ancients were well aware that to heal the soul, or even the body, a certain assistance from psychic experiences was necessary. ~Carl Jung, Psychology of Yoga and Meditation, Page 53