The Magic Spyglass is a tool of Kaliko, the High Chamberlain of the Nome Kingdom.
It consists of a tube in the rock wall of the Nome King's throne room. The tube runs up to the side of a mountain and turns several curves, but since it is magic Kaliko can see through it as easily as if it had been straight.
Kaliko used to Magic Spyglass to identify the Shaggy Man and his companions, who were on their way to the Nome Kingdom to rescue his brother. (Tik-Tok of Oz)