I lightly placed my finger a quarter of the length down the E-string of a violin and drew the bow, forcing the third harmonic. I used an oscilloscope app to look at the waveform. I got this unusually regular pure pattern: https://drive.google.com/file/d/0B9KQ4zoXAY2AQkU1dVowWjRCUTA/view?usp=sharing It looks almost like two waves a semitone apart are superimposed, but I can only hear one note. The same pattern occurs when the finger is placed on any of the nodes of the third harmonic, and a similar pattern occurs on the A-string, but with a lower frequency. How is this happening?