Jamieson, Fausset and Brown on Daniel 5:7

7. He calls for the magicians, who more than once had been detected in imposture. He neglects God, and Daniel, whose fame as an interpreter was then well-established. The world wishes to be deceived and shuts its eyes against the light [Calvin]. The Hebrews think the words were Chaldee, but in the old Hebrew character (like that now in the Samaritan Pentateuch).

third ruler--The first place was given to the king; the second, to the son of the king, or of the queen; the third, to the chief of the satraps.