A crystal ball, also known as an orbuculum, is a crystal or glass ball and common fortune telling object. It is generally associated with the performance of clairvoyance and scrying in particular.
The earliest use of a crystal ball can be first attributed to the Celtic Druids who divined the future and omens with beryl balls.
In the 1st century AD, Pliny the Elder describes use of crystal balls by soothsayers ("crystallum orbis", later written in Medieval Latin by scribes as orbuculum). By the 5th century AD, scrying was widespread within the Roman Empire and was condemned by the early medieval Christian Church as heretical.
Dr. John Dee was a noted British mathematician, astronomer, astrologer, geographer, and consultant to Queen Elizabeth I. He devoted much of his life to alchemy, divination, and Hermetic philosophy, of which the use of crystal balls was often included.
Crystal gazing was a popular pastime in the Victorian era, and was claimed to work best when the Sun is at its northernmost declination. Immediately before the appearance of a vision, the ball was said to mist up from within.
The art or process of "seeing" is known as "scrying", whereby images are claimed to be seen in crystals, or other media such as water, and are interpreted as meaningful information. The "information" gleaned then is used to make important decisions in one's life (i.e. love, marriage, finances, travel, business, etc.).
When the technique of scrying is used with crystals, or any transparent body, it is known as crystallomancy or crystal gazing.