Kirchhoff's law of thermal radiation rarefied material such as air, or transparent material, through which observations can be made. The interface is not a material body and can neither emit nor absorb. It is a mathematical surface belonging jointly to the two media that touch it. It is the site of refraction of radiation that penetrates it and of reflection of radiation that does not. As such it obeys the Helmholtz reciprocity principle. The opaque body is considered to have a material interior that absorbs all and scatters or transmits none of the radiation that reaches it through refraction at the interface. In this sense
A Moving Sound A Moving Sound A Moving Sound () or Sheng Dong is a Taiwanese music act consisting of vocalist/dancer Mia Hsieh, vocalist, bass guitarist and zhong ruan player Scott Prairie, erhu player I-Fang Chen, and zhong ruan player Chih-Ling Chen. In A Moving Sound’s music traditional Taiwanese music forms are reinterpreted to create new original song compositions. Instruments such as the erhu (fiddle), the zhong ruan (lute), and the transcendent vocals and dance of lead singer Mia Hsieh, transport listeners on a journey that Global Rhythm magazine described as “...delicately balanced between many worlds…an entryway to Eastern music and artful expression