You will reach a room with huge spherical device in it; follow Paratus to the top, and he will tell you to place the Crystal in the device and after you do that, to attune the crystal using fire and frost spells. You are ready when the beams coming from the crystal are pointing into the middle of each of three rings on the celling. Note: You have to use Frostbite and Flames, any other fire or frost spells do not work, (i.e. frost spike aims the beams in the wrong area). The room with the Oculory contains a copy of each Spell Tomes.