You're too late--though there's nothing you could have done. When you solve the elevator puzzle and reach the upper floor of the dome, Saavedro completes his business and links to an unknown location. A cage encloses the linking book that he just used; the cage lowers into a pit in the room's center. You won't be able to reach or open the cage.
Walk toward the center of the room and locate the blue button above the pit. Press the blue button to trigger a message from Atrus. He addresses you as his "sons" and discusses the purpose of this age (and apparently the others you can link to from J'nanin). However, before Atrus can complete his speech, Saavedro breaks in with his own speech. Saavedro has stolen the Releeshahn book, and to find Saavedro and the book, you must retrieve three symbols--one from each of the ages linked from J'nanin.
The message from Atrus and Saavedro isn't the only important thing inside the dome. Search the walls for three telescopelike devices, and you'll discover that the dome could technically be called an observatory--though the telescopes aren't pointed at a sky, but instead at important landmarks in J'nanin.
Though the specific solution is different, you will solve each of the telescopes in a similar fashion. Examine the telescope screen carefully and note the symbol on the view screen. You are searching for that same symbol somewhere in J'nanin--you shouldn't have to look hard, however, because the symbol is positioned on the landmark within your view. Each telescope is pointed at a specific white tusk that you may have seen outside during your exploration of J'nanin.
SAAVEDRO'S JOURNAL: Search the observatory's top floor for a page from Saavedro's journal.
Your goal is to adjust the position, the zoom, and the focus of each telescope so that you have aligned the symbol on the view screen with the symbol on the tusk.
1. To adjust the position, put the mouse cursor over the view screen and click and drag the view around until you are aligned correctly. You should adjust the view screen until the tusk and its symbol appear within the view.
2. To adjust the zoom, maneuver the handle on the right side. Adjust the position and zoom until the symbol on the tusk lies within the symbol on the view screen.
3. To adjust the focus, maneuver the handle on the left side. With a combination of the position adjustment, the zoom, and the focus, you should be able to align the symbol on the view screen with the symbol on the tusk.
You should also notice that adjusting the position, zoom, and focus also moves the small spheres around the telescope view screen. These small spheres create the code required to open the linking books for the three ages connected to J'nanin.
Here are the completed telescope puzzles and their codes:
 A completed telescope code. |  Another completed telescope code. |  The third completed telescope code. |
Once you complete all three telescopes, you're ready to tackle the remaining J'nanin puzzles and to open the linking books to three different ages. Once you complete one puzzle, you can visit the new age and complete its tasks before returning to J'nanin. Or, you can remain at J'nanin and solve all its puzzles to uncover all three linking books before you leave.