Where can I find the lexicon machine for "Discerning the Transmundane"?

Solution 1:

The giant golden globe roughly in the centre of Blackreach is not the lexicon machine, but it provides a useful point of reference to find it. While standing below the giant golden globe, walk directly south. As you pass through the southern gate of the wall, you will be on top of a set of stairs. Slightly to your right is a tall tower that connects to the ceiling. This is the Tower of Mzark. To reach it, you will cross a bridge over rapids which flow to the edge of a waterfall. When you reach the tower, take the elevator to the tower's interior, solve the puzzle, and you will be able to transcribe the Elder Scroll into the lexicon and then retrieve the Elder Scroll from the machine.

Solution 2:

The Tower of Mzark is in the southwest of Blackreach near the Farm Overseer's House. You'll use the elevator to get to the lexicon machine.