OK, the first force field. You probably guessed it has something to do with the spheres you find. There's a power source for them upstairs, go up and turn on the power. Then you can activate either sphere by flipping the handle between them.

But now what symbols do you press? Look through your notes about the three levels. There are phrases that Atrus mention that are listed on the walls. They are:

1. Energy powers future motion
2. Nature encourages mutual dependence
3. Dynamic forces spur change
4. Balanced systems stimulate civilizations

Also, each world you solved ended in a symbol. So now put each page worth of symbols into one of the circles (choose one, any one). Just start each phrase with the top spot. and work clockwise. You can figure out what the missing symbols are by looking on the walls. So fill three circles with 3 sets of symbols. Everything but #4 goes in.

Once you get them all right, the force field powers off.

The Myst 3: Exile Walkthrough