What causes a glass to ring when you run your finger along the rim of it?

[Profanity and Symbols]

Have you ever tried this? It works especially well with a wine glass. You lick your finger, make sure the rim is clean, and run your finger along the rim. It makes this ringing sound that reminds me of something a monk would meditate to. It works also with a pipe, running your finger down it. Anyone know why this happens? Thanks.