You've probably run the tips of your fingers around the edge of a wine-glass to produce sound. When the level of liquid is changed so is the note that emanates from the glass. This phenomenon was known for centuries (maybe millenia) but it wasn't until the 18th. C that the idea really took off in the realm of professional performance. Benjamin Franklin is believed to have been the inventor of the glass harmonica in its current form: a series of glass bowls on a spindle set within an upright case resembling a piano. Over a hundred composers from the Age of Enlightenment wrote music for Franklin's invention.
The sound is eerie and ethereal and some of Franklin's contemporaries believed it was also dangerous, especially to those with melancholy dispositions:
"There may be various reasons for the scarcity of armonica players, principally the almost universally shared opinion that playing it is damaging to the health, that it excessively stimulates the nerves, plunges the player into a nagging depression and hence into a dark and melancholy mood, that it is an apt method for slow self-annihilation… Many (physicians with whom I have discussed this matter) say the sharp penetrating tone runs like a spark through the entire nervous system, forcibly shaking it up and causing nervous disorders."
- Friedrich Rochlitz, 1798
It is interesting that Rochlitz describes the sounds' effect on the nerves in the language of electricity, another "discovery" of the Age of Enlightenment and one closely tied to the glass harmonica's creator Benjamin Franklin. One can sense how close we're getting to the modern description/understanding of electro-chemical biological processes.
Listen to the short piece below written for glass harmonica by none other than Mozart. Of course, if you're melancholy by nature, you may want to skip it.