Instructions on how to rotate the tower in Myst library and get the access key to unlock the sunken ship.
Rotate the Tower
In the library on Myst, look at the painting of Myst Island and click and hold the blinking circle to make the tower rotate. Make the line turn red at the mast of the sunken ship at the dock. After you rotate it to point there, click the portrait of the staircase to make the bookshelf turn into stairs, and go up the elevator at the end.
Go up the key ladder to see the clue for the sunken ship:
October 11, 1984
January 17, 1207
November 23, 9791
This clue may remind you of the circular building with the emblem on the door near the dock (if you went in). Before you go there, you may wish to review the unburned book in the upper-right of the bookshelf of the library.
When you're ready, go into the circular building near the dock. Turn around and press the switch next to the door to turn off the lights. Then sit in the chair and check on the device up above to lower it.
Use the sliders on the right to change the displayed date. Make the date match each of the three dates that were shown in the tower. Then press the blinking button.
The first date matches the leaf constellation from the book. The second date matches the serpent constellation from the book. The third date matches the insect constellation from the book.
Go outside, and go to the area in front of the library, where there are raised cubes on either side of the path. Check on each one to find the leaf, serpent, and insect. Click each one to turn it green. When you have turned all three green, the sunken ship in the fountain in the middle will rise.
Go back to the sunken ship at the dock where you started the game, and you will find that this ship has risen out of the water as well. Step onto the deck, then walk down the stairs to the right, open the door, and use the book on the chair to go to the Stoneship Age.