What is the first science fiction/fantasy world that used a seeing stone or magic mirror in a way where a message/connection is duplicated across multiple endpoints at the same time?
I know the Lord of the Rings Seeing Stones (Palantir) could hypothetically connect with multiple other Seeing Stones simultaneously, but in my limited memory of The Lord of the Rings, I don't remember that ever taking place in writing. So, that wouldn't count. I am assuming that Tolkien drew from prior (ancient?) works in using that concept; perhaps one of them might have such an example.