The glass harmonica had only a short bit of popularity before the urban legends of the early 19th century killed it. It was said that listening to or playing the instrument would make you insane; the audience had strange experiences, many fainting or being overwhelmed with emotion. After the death of a child during a concert, glass harmonicas were actually banned as a public danger in some places. On the other hand, glass music has recently been embraced by New Age followers -- the strange vibrations deemed so deadly before are now considered healing.
One of the reasons for the mystical responses to the instrument may be explained by science. Apparently the brain has two ways of interpreting where and what a sound comes from, decided by the frequency of the sound, and the timbre of the glass harmonica exists mainly in the realm between. The brain has a hard time deciding where the sound is actually coming from. I imagine the subconscious confusion would make some people feel insane, and others feel off-balance in a pleasurable, ethereal way.
I personally find myself slipping into a trance-like state when I listen to glass music. I tend to believe there is some truth to all legends; of glass music, I think it isn't true that it causes you to go mad, but it is true that it has an intensifying effect. Like mind-altering substances, it brings out what's hidden within.
(sample from finkenbeiner.com; artist is William Wilde Zeitler)
LJ idol topic 6: "Urban Legends" ((will add voting link later))