Science Lesson: Every material on Earth has a resonant frequency. If you put energy into a material at its resonant frequency, you will force it to resonate. When you apply a dose of molecular energy to glass — like running your finger along the rim — it causes air molecules to vibrate at the same frequency as the glass, which then produces different tones. Depending on how much liquid is in the glass, a different tone will be produced. These Major Scale Musical Wine Glasses have a full scale labeled with sandblasted fill lines, which allows you to control the note and play any song in the key of A-major. Science is freakin' awesome.