L. Frank Baum

“ Glinda answered, assuringly. "We shall still be able to see each other and everything in the Land of Oz. It won't affect us at all; but those who fly through the air over our country will look down and see nothing at all. Those who come to the edge of the desert, or try to cross it, will catch no glimpse of Oz, or know in what direction it lies. No one will try to tunnel to us again because we cannot be seen and therefore cannot be found. In other words, the Land of Oz will entirely disappear from the knowledge of the rest of the world."
"That's all right," said Dorothy, cheerfully. ”

“ And also it told me you were all coming to my castle, and why."
"Then," said Ozma, "I suppose you know what is in my mind, and that I am seeking a way to prevent any one in the future from discovering the Land of Oz."
"Yes; I know that. And while you were on your journey I have thought of a way to accomplish your desire. For it seems to me unwise to allow too many outside people to come here. Dorothy, with her uncle and aunt, has now returned to Oz to live always, and there is no reason why we should leave any way open for others to travel uninvited to our fairyland. ”

“ I myself have been thinking of this very idea, and it seems to me there are entirely too many ways for people to get to the Land of Oz. We used to think the deadly desert that surrounds us was enough protection; but that is no longer the case. The Wizard and Dorothy have both come here through the air, and I am told the earth people have invented airships that can fly anywhere they wish them to go. ”