I found this nice little "final puzzle" summary. Take a read:

"Do not attempt this unless you have already trapped Gehn and freed Catherine!
First, turn on the power to the telescope by turning the steam valve in side 2
of the gate room. Next, use the code in Catherine's journal to open the hatch
beneath the telescope. [OUT-OF-RIVEN NOTE: This code is randomly generated for
each game file, so it cannot be given here.] The code shows which button to
push, NOT how many times you should push each button. For example, if the code
is 4 3 5 2 1, press the fourth button, then the third, then the fifth, etc.
Once the hatch is open, look on the base of the left support strut for a small
metal rod, and swing it away. Now, turn the handle next to the button (at the
end of the circular pipe surrounding the telescope) so it is pointing down,
then press the button, which will lower the telescope a few inches. Keep
pressing the button until the telescope breaks the glass."

Note the underlined statement above. I believe the gate room is the room that rotates. Remember the left side passage where there is a steam valve? If this is not set, then you won't hear that loud hissing noise that you may notice in the video posted above.

I hope this helps.

Dadguy :-)

PS: I noticed today that the link to Graham's walkthrough was dead. It seems his domain is no longer active.

Thanks, dadguy.

Chief not sure what you mean how do I steam power it??

monbron, if you read dadguy post just above and you remember the beginning of the game with the rotating room and the passage (down the stairs) that you access by passing under a fence, when you go at the end of the passage, you will see the steam valve with the icon of the telescope.


Good luck.

Chief

Ok folks - THANK YOU I've finished, and you were all right I did not have the valve turned. So on to Myst 3 for the 2nd time, look out for all the calls for help especially Dadguy!!