Telescope

Background
In the tower of Manannan's house, there is a small observatory containing a telescpe. Alexander-Gwydion says that Manannan could look through it and spy on anyone or any place he wished. Derek Karlavagen, who lives in that house now, confirms this report.

In the Arabian Nights story about the three brothers wanting to marry the same princess, one of the princes came upon just such a telescpe, and it was through its power that they were able to discover their princess near death. They then flew the magic carpet to her side and cured her with the magic fruit.