A Ray is spell that travels to a target through a straight line of sight. There is no limit to the distance that a Ray may travel.
A Ray spell may travel through multiple targets. To do this the pool of successes is spent on each target in sequence.
Example: Trogdor the Archmage of Draconic Burnination Fires a Ray of Brimstone at an approaching horde of Minotaurs. He rolls 6 successes. He can then choose to distribute his successes among targets in the line of fire, but must destroy an entire pip of the nearest target before the spell has done enough damage to penetrate to the next target.