Li Zhengdao once commented on Helmholtz: physics and music, sound waves and scientific symphonies. Helmholtz truly combined art and science, music and physics with the thoughts of scientists and artists closely and organically. He initiated the field of music physics, and published many papers in this field, such as On the Combined Tone (1856), On the Physical Causes of Harmony Interval and Disharmony Interval (1858), On the Vowel Sound Quality (1859) and On the Open Tube Vibration.