The Britannica Blog has a Maine library on its list of haunted United States libraries. The text it quotes comes directly from page 560 of The Whole Library Handbook 4 by George M. Eberhart (also the author of the blog post), which you can see online at Google Books here.To quote the source: "Eliot, William Fogg Library. A newspaper photo apparently shows a transparent skull floating above a staircase." This same quote appears on the Spirits of Maine page, with the addition of the following: "Also window randomly broke while kids were playing outside."
I haven't found anything else explaining this online. Perhaps an inquiry is in order.
