It's not really magic, but the radio-sensitive crystals react to the minute electrical waves emitted by the brain. They establish a contact with the personality I think of! 
The Orb of Nabu is a mystical globe of crystal used by Dr. Fate to learn about dangers and the unknown in general.
History
The crystal would be kept inside the Tower of Fate, but it could also be summoned by Fate at will and it would travel across the air to reach the summoner.[1]
Notes
- Doctor Fate first used a crystal ball to communicate with Inza Cramer in More Fun Comics #59. Fate started using a crystal ball frequently, but the item was not properly given its name until The Flash #305.
See Also
- Appearances of Orb of Nabu
- Item Gallery: Orb of Nabu
- Images featuring Orb of Nabu