Shy ghost in the stack

"It was a February evening and I went to the 8th floor of the stack to look for a couple of books. The first book was in a room at the southern end of the building. As I knelt down to look for the book I felt a very light touch on my left shoulder as if my cardigan had been pulled slightly away from my skin. There was obviously nobody there but I felt a little odd and a little scared, so quickly found the book and left the room [...] I cannot explain what happened. I was not close to the other shelving and there was nothing behind me." NB: the Harry Price Library was for many years housed on the 8th floor.