GEARS PUZZLE
Put the red line at the gear. Go to the picture of a hallway on the wall. Press it. This will lower the bookcase and reveal a secret passage. Follow it to the elevator. Get inside, close the door, and go up to the tower.
There are two ladders here--one with a picture of a key, and one with a book. If you go up the book ladder, you will see the location of the liking book. Up the key ladder is the clue needed to get it. The clue for this Age is the time, 2:40 and the numbers 2,2,1. Go back down the elevator and into the library. Click on the picture of the Library's door. Exit the library and go down to the Clock Tower. The two red wheels change the time shown on the clock. The large wheel manipulates the hour, the small the minutes. Set the clock to 2:40 and press the button. Cross the bridge, flip the marker switch, and enter the tower.
The numbers that must show on the wheels are, of course, 2, 2, 1. The left lever controls the bottom two wheels while the right controls the top two. You can use these levers until the counterweight hits the floor. Note the lever in the right corner. This resets the puzzle. Pull down the left lever, then the right. Pull down the right again, but this time holding it until the middle number reads 2. You now have access to Mechanical Age. Go to the Gear. Inside is the book.